TBI with 7749 and $8D S_AUJP
12-07-2014, 06:49 PM
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TBI with 7749 and $8D S_AUJP
I've been working on an interesting project! It's a 1967 Camaro SS, 350 engine, manual transmission car. Friend bought it with a really bad running engine!
He has seen my TBI 72 Nova and wanted to put TBI on his car. The goals for the project were to use as much on-hand materials as possible. As such, the engine is not completely well matched. I am hoping to be able to tune around some of the shortcomings!
To that end, I wanted a good ECM program that could do wideband datalogging and had high-speed ALDL data link. I've done several Buick and Chevy V6 turbo builds, and had good success with Code59. This car won't be turbocharged, so I opted for a 1-bar setup.
I found Super $8D looked like what was needed. The research about running TBI with it showed some interesting things. There was a lot of information about Cylinder Select, distributor reference pulses per injection pulse, MEMCAL's and software.
In the end, I decided to give it a try and wire it up. I was able to get the 7749 ECM to fire in TBI alternating mode, without Cylinder Select error (41). EDIT: It did not work as it appeared. Only one of the 2 drivers worked with $8D code. Will be changing to use Code $59 which operates both drivers properly.
As said, there is a very large amount of information out there, so I will try to distill it down as simple as possible!
There were 3 modifications (aside from tuning) to enable TBI on a 7749:
1 - Wiring harness (peak and hold)
2 - MEMCAL (Cylinder Select)
3 - Program (fueling mode)
I started with a TBI harness pinned for a 1227747 ECM. I re-pinned it as for a 1990 TPI setup with 7730 ECM, (wired for S_AUJP $8D) with the exception of the injector circuit.
The 7749 ECM will run the same programs as the 7730, but it has dual injector drivers, with peak and hold capability. To use this, the injectors were wired as follows:
Injector 1 to ECM C11
Injector 2 to ECM C10
Injector Jumper 1 D5 to D6
Injector Jumper 2 C13 to C15.
No ground to D7.
By removing any ground wires from the jumper points, and installing the jumpers - this puts the drivers in Peak and Hold mode. This will allow it to operate the TBI without burning out anything.
To get the ECM to fire the injectors in TBI mode, the Cylinder Select signal from the MEMCAL must be set for TBI mode. This will make the ECM fire the injectors once every other reference pulse, when controlled by hardware.
On Gearhead EFI forum, I found this thread showing the MEMCAL cylinder select settings.
My MEMCAL is for a Buick V6 (closest knock filter I could find to a Chevy V8 in my junk box - will have to see if this works, I don't know yet). To change it to a TBI MEMCAL, I cut the pin from the original resistor chip to the MEMCAL pin 56. Then, from there, installed the resistors as shown on the page linked above. The circuit looks like this:
(Pin 53) --15K--(Pin 56)--7.5K--(Pin 58)
To make the software work in TBI mode, the fueling mode must be selected to match the MEMCAL.
As for the engine, it's a unique mix of parts. I hope I can tune it to be streetable. My friend wanted to keep as many of the original parts that came with the car. It has sentimental value to look similar to how it did when he got the car.
It's a 350, 4-bolt main block with aftermarket rods, steel crankshaft and forged pistons.
The heads are early Chevy Bowtie heads. They have been ported. Due to the very bad craftsmanship of the previous mechanics, the engine ended up with bent valves. They had a horrible race-in-your-face flat tappet solid lifter cam. There was no power until over 3500 RPM. There was no idle....
The new cam is a Comp Cams 260XFI-HR13. This is supposed to give very good low and midrange power. It should also make the engine easier to tune since it's specifically designed for EFI engines.
The intake is an early Edelbrock Victor Jr. air gap manifold. This is the part I am concerned is not well matched to the rest of the engine. The problem is, the heads and manifold are ported together, and a regular manifold won't cover the ports on the head. The intake ports have been hogged out.
The TBI is from a 454 pickup. It has injector pod spacer and the stock 80.5 Lb /Hr injectors.
Exhaust manifolds are reproduction rem's horn iron manifolds. Hopefully they will be more reliable than the leaky, noisy headers the engine had on it. My only concern is if they clear the air conditioner box.
As this project comes together, I'll post more here!
Sincerely,
David
He has seen my TBI 72 Nova and wanted to put TBI on his car. The goals for the project were to use as much on-hand materials as possible. As such, the engine is not completely well matched. I am hoping to be able to tune around some of the shortcomings!
To that end, I wanted a good ECM program that could do wideband datalogging and had high-speed ALDL data link. I've done several Buick and Chevy V6 turbo builds, and had good success with Code59. This car won't be turbocharged, so I opted for a 1-bar setup.
I found Super $8D looked like what was needed. The research about running TBI with it showed some interesting things. There was a lot of information about Cylinder Select, distributor reference pulses per injection pulse, MEMCAL's and software.
In the end, I decided to give it a try and wire it up. I was able to get the 7749 ECM to fire in TBI alternating mode, without Cylinder Select error (41). EDIT: It did not work as it appeared. Only one of the 2 drivers worked with $8D code. Will be changing to use Code $59 which operates both drivers properly.
As said, there is a very large amount of information out there, so I will try to distill it down as simple as possible!
There were 3 modifications (aside from tuning) to enable TBI on a 7749:
1 - Wiring harness (peak and hold)
2 - MEMCAL (Cylinder Select)
3 - Program (fueling mode)
I started with a TBI harness pinned for a 1227747 ECM. I re-pinned it as for a 1990 TPI setup with 7730 ECM, (wired for S_AUJP $8D) with the exception of the injector circuit.
The 7749 ECM will run the same programs as the 7730, but it has dual injector drivers, with peak and hold capability. To use this, the injectors were wired as follows:
Injector 1 to ECM C11
Injector 2 to ECM C10
Injector Jumper 1 D5 to D6
Injector Jumper 2 C13 to C15.
No ground to D7.
By removing any ground wires from the jumper points, and installing the jumpers - this puts the drivers in Peak and Hold mode. This will allow it to operate the TBI without burning out anything.
To get the ECM to fire the injectors in TBI mode, the Cylinder Select signal from the MEMCAL must be set for TBI mode. This will make the ECM fire the injectors once every other reference pulse, when controlled by hardware.
On Gearhead EFI forum, I found this thread showing the MEMCAL cylinder select settings.
My MEMCAL is for a Buick V6 (closest knock filter I could find to a Chevy V8 in my junk box - will have to see if this works, I don't know yet). To change it to a TBI MEMCAL, I cut the pin from the original resistor chip to the MEMCAL pin 56. Then, from there, installed the resistors as shown on the page linked above. The circuit looks like this:
(Pin 53) --15K--(Pin 56)--7.5K--(Pin 58)
To make the software work in TBI mode, the fueling mode must be selected to match the MEMCAL.
As for the engine, it's a unique mix of parts. I hope I can tune it to be streetable. My friend wanted to keep as many of the original parts that came with the car. It has sentimental value to look similar to how it did when he got the car.
It's a 350, 4-bolt main block with aftermarket rods, steel crankshaft and forged pistons.
The heads are early Chevy Bowtie heads. They have been ported. Due to the very bad craftsmanship of the previous mechanics, the engine ended up with bent valves. They had a horrible race-in-your-face flat tappet solid lifter cam. There was no power until over 3500 RPM. There was no idle....
The new cam is a Comp Cams 260XFI-HR13. This is supposed to give very good low and midrange power. It should also make the engine easier to tune since it's specifically designed for EFI engines.
The intake is an early Edelbrock Victor Jr. air gap manifold. This is the part I am concerned is not well matched to the rest of the engine. The problem is, the heads and manifold are ported together, and a regular manifold won't cover the ports on the head. The intake ports have been hogged out.
The TBI is from a 454 pickup. It has injector pod spacer and the stock 80.5 Lb /Hr injectors.
Exhaust manifolds are reproduction rem's horn iron manifolds. Hopefully they will be more reliable than the leaky, noisy headers the engine had on it. My only concern is if they clear the air conditioner box.
As this project comes together, I'll post more here!
Sincerely,
David
Last edited by turbokinetic; 01-15-2015 at 01:23 PM.
12-07-2014, 07:05 PM
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Re: TBI with 7749 and $8D S_AUJP
Here are some pictures.
This is the car, before the engine was pulled out. You can't really tell from the picture, but there was a mishap, and the transmission is broken. It appears the car hit high-center on the bellhousing, and cracked the housing.
The engine with TBI:
Injector jumpers (the small yellow loops of wire at the right-side connector):
The modified MEMCAL. (excuse my soldering! This was just a test to see if this was workable concept):
The floor:
This is the car, before the engine was pulled out. You can't really tell from the picture, but there was a mishap, and the transmission is broken. It appears the car hit high-center on the bellhousing, and cracked the housing.
The engine with TBI:
Injector jumpers (the small yellow loops of wire at the right-side connector):
The modified MEMCAL. (excuse my soldering! This was just a test to see if this was workable concept):
The floor:
12-07-2014, 08:35 PM
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Re: TBI with 7749 and $8D S_AUJP
Video of testing:
EDIT: The video is misleading, this did not actually function as intended. If you are interested, the link is here:
EDIT: The video is misleading, this did not actually function as intended. If you are interested, the link is here:
Code:
https://www.youtube.com/watch?v=E0djLt_lsX4
Last edited by turbokinetic; 01-15-2015 at 01:16 PM.
01-15-2015, 01:12 PM
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Re: TBI with 7749 and $8D S_AUJP
Hey folks - I am very sorry to have posted this before I did further testing. There is a problem with the $8D code and the 7749 ECM.
Without going into great detail, the problem is the second injector driver of the 7749 ECM will not work with $8D software.
If two injectors are connected to the 1227749 ECM, one will be under $8D software control, the other will be under MEMCAL limp-home control.
With $8D in a 1227749 9ECM, it will only properly actuate the U13 injector driver. This one is the injector driver which exits the ECM on connector C11/C12. It is the one which is also present on the 1227730 ECM.
The other injector driver (only present on the 1227749) comes out on the ECM connector pin C10. It is controlled by U15 and this one remains in limp mode when the ECM is running $8D. It will fire its output based on the MEMCAL only.
I was able to put the software and hardware in "TBI mode" using the modified MEMCAL. At first appearance, this appeared to be working. The trouble was, the second injector driver (U15) was always operating on the MEMCAL (limp home mode) fuel delivery, while the U13 injector driver was operating under $8D software control.
I have studied the 1227749 internal schematic and see where the signal for the U15 injector driver is processed further before it goes to the driver input.
So in summary; With $8D in a 1227749 9ECM, it will only properly actuate the U13 injector driver. This one is the injector driver which exits the ECM on connector C11/C12. It is the one which is also present on the 1227730 ECM.
The other injector driver (only present on the 1227749) comes out on the ECM connector pin C10. It is controlled by U15 and this one remains in limp mode when the ECM is running $8D. It will fire its output based on the MEMCAL only. I did not test the pulse width, but using noid lights it was giving noticeably more pulsewidth, and I could not change it by adjusting the program settings for injector constant. The other injector was responding.
The good news is, using $59 will actuate both injectors correctly under software control without issue.
If I was a code genius (which I am not) I could compare the $8D and the $59 and figure out what needs to be done to enable the second driver in $8D. But I'm not there yet, so I will have to abandon the $8D/TBI adventure for now.
It's probably going to make my life easier anyway because I have quite a bit of experience with $59 and have a turbo TBI project coming up eventually. So if I learn the TBI specific quirks of it, it will help me later on down the road.
Once again, sorry I posted misinformation earlier on. I hope my findings will help someone else who is capable of comparing the codes to work this problem out in the future.
I will be updating this thread as the car gets together. We're waiting on exhaust manifolds and a driveshaft yoke. You probably saw the new manifolds on the video? They were specifically touted as fitting this car, but the left manifold hits the steering box.
The engine is in the car and all fuel and electrical is hooked up.
Sincerely,
David
Without going into great detail, the problem is the second injector driver of the 7749 ECM will not work with $8D software.
If two injectors are connected to the 1227749 ECM, one will be under $8D software control, the other will be under MEMCAL limp-home control.
With $8D in a 1227749 9ECM, it will only properly actuate the U13 injector driver. This one is the injector driver which exits the ECM on connector C11/C12. It is the one which is also present on the 1227730 ECM.
The other injector driver (only present on the 1227749) comes out on the ECM connector pin C10. It is controlled by U15 and this one remains in limp mode when the ECM is running $8D. It will fire its output based on the MEMCAL only.
I was able to put the software and hardware in "TBI mode" using the modified MEMCAL. At first appearance, this appeared to be working. The trouble was, the second injector driver (U15) was always operating on the MEMCAL (limp home mode) fuel delivery, while the U13 injector driver was operating under $8D software control.
I have studied the 1227749 internal schematic and see where the signal for the U15 injector driver is processed further before it goes to the driver input.
So in summary; With $8D in a 1227749 9ECM, it will only properly actuate the U13 injector driver. This one is the injector driver which exits the ECM on connector C11/C12. It is the one which is also present on the 1227730 ECM.
The other injector driver (only present on the 1227749) comes out on the ECM connector pin C10. It is controlled by U15 and this one remains in limp mode when the ECM is running $8D. It will fire its output based on the MEMCAL only. I did not test the pulse width, but using noid lights it was giving noticeably more pulsewidth, and I could not change it by adjusting the program settings for injector constant. The other injector was responding.
The good news is, using $59 will actuate both injectors correctly under software control without issue.
If I was a code genius (which I am not) I could compare the $8D and the $59 and figure out what needs to be done to enable the second driver in $8D. But I'm not there yet, so I will have to abandon the $8D/TBI adventure for now.
It's probably going to make my life easier anyway because I have quite a bit of experience with $59 and have a turbo TBI project coming up eventually. So if I learn the TBI specific quirks of it, it will help me later on down the road.
Once again, sorry I posted misinformation earlier on. I hope my findings will help someone else who is capable of comparing the codes to work this problem out in the future.
I will be updating this thread as the car gets together. We're waiting on exhaust manifolds and a driveshaft yoke. You probably saw the new manifolds on the video? They were specifically touted as fitting this car, but the left manifold hits the steering box.
The engine is in the car and all fuel and electrical is hooked up.
Sincerely,
David
05-02-2015, 07:55 PM
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Re: TBI with 7749 and $8D S_AUJP
I am using a 3-bar MAP for several reasons. The latest version of Code 59 is designed for it, and that's what I have been using. I have tuned 4 custom turbo system swith $59 and so I have a pretty good hang of it and the tuning software.
I know a 3-bar MAP on a N/A engine loses table resolution etc. etc. and it can be debated to the end of the earth. But in the end, boosted cars run just fine at off-idle and so there must be enough resolution there or those would not run well until you hit boost.
I will go into detail about tuning the injector battery offset, once we have an exhaust system in place. That will be the biggest difference between the high-Z and low-Z systems.
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05-02-2015, 08:07 PM
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Re: TBI with 7749 and $8D S_AUJP
Thanks. The car is a friend's car and he wanted to use this combination of parts which I realize are not a 100% matched setup. But, I believe it will definitely be drivable more than it was before.
I am using a 3-bar MAP for several reasons. The latest version of Code 59 is designed for it, and that's what I have been using. I have tuned 4 custom turbo system swith $59 and so I have a pretty good hang of it and the tuning software.
I know a 3-bar MAP on a N/A engine loses table resolution etc. etc. and it can be debated to the end of the earth. But in the end, boosted cars run just fine at off-idle and so there must be enough resolution there or those would not run well until you hit boost.
I will go into detail about tuning the injector battery offset, once we have an exhaust system in place. That will be the biggest difference between the high-Z and low-Z systems.
I am using a 3-bar MAP for several reasons. The latest version of Code 59 is designed for it, and that's what I have been using. I have tuned 4 custom turbo system swith $59 and so I have a pretty good hang of it and the tuning software.
I know a 3-bar MAP on a N/A engine loses table resolution etc. etc. and it can be debated to the end of the earth. But in the end, boosted cars run just fine at off-idle and so there must be enough resolution there or those would not run well until you hit boost.
I will go into detail about tuning the injector battery offset, once we have an exhaust system in place. That will be the biggest difference between the high-Z and low-Z systems.
05-02-2015, 09:07 PM
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Re: TBI with 7749 and $8D S_AUJP
Yes, but $59 still has the 1 BAR hold over from $58, which is why I asked if you tried that. I'm not so worried about the resolution, just whether the 1 BAR ability works as well as it would with $58, when 1 BAR is selected. I went through and set up a 1 BAR XDF and ADX a few years ago because I planned to test it on a project that hasn't gotten that far yet. I was hoping that you went that way and could report on it so that I could know whether it was worth it or not. lol
I did consider the 1-bar MAP with $59, and researched it quite a lot. The problem I found was, the 1-bar function seems to not support some of the added features of $59. I found some posts from the guys on the Code59.org forum, where they explained it. Seems the scaling for 3-bar is hard-coded into the program in certain areas.
Since I have done so many turbo projects, I have spare 3-bar MAP sensors just kicking around my barn. It was just the easiest way for me at the time in my situation.
The only problem I noticed is, the reported RPM on the ALDL is showing 6000+ whenever the engine is running. I don't know if it's got to do with the cylinder select modifications or what could have happened. The timing moves around like it is actually reading RPM correctly internal to the code. Will have to experiment with this part of it.
I got the exhaust pipe fabricated to go around the steering shaft; as well as got the shaft welded together and installed. That leaves me with the hydraulic lines from the steering gear to the pump. They don't appear that they will be too crazy to make up. I found all the fittings to make up the pressure line, but the return uses a smaller size fitting. I may have to buy a factory made return line and cut it up and modify it.
The original steering gear had inverted flare fittings. The new rack and pinion gear has bump-tube O-ring ports.
Thanks,
David
05-02-2015, 11:51 PM
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Re: TBI with 7749 and $8D S_AUJP
I haven't read what you have about the hard coding of the 3 BAR stuff, I guess. On my bench everything seemed to work fine in 1 BAR mode and use the extended tables. I still need to test on an actual engine to verify though.
05-16-2015, 02:39 PM
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Re: TBI with 7749 and $8D S_AUJP
I've been driving the 67 Camaro and it's running so-so but I am having problems with the ignition system. It is a normal external-coil HEI. The distributor (purchased by my friend) is an aftermarket unit with a different type of pickup coil. It uses a normal GM HEI module, though. Yesterday the module failed, leaving the car non-running. After changing the module, the car starts right up. The engine will run very well above 1200 RPM. If I let it idle, the tach needle will twitch and jump around. The ECM will register intermittent glitches of 6000+ RPM. When this happens, the engine misfires.
I have checked grounds, checked wiring, checked for plug wires too close to the harness, and can find nothing.
Have swapped another ECM and it made no difference.
I made this video so that you can see what I am talking about. If anyone has seen this before, or have any ideas, please let me know!
Sincerely,
David
Video link:
05-16-2015, 04:24 PM
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Engine: check
Transmission: check
Re: TBI with 7749 and $8D S_AUJP
To be honest, get a GM small cap distributor. They just work. If you find a decent one in the JY and it has an aftermarket ICM, swap the GM ICM you have into it. It has been a bit since I looked but AC Delco distributor shafts are still available.
As for the misfire, it is likely caused by the pickup coil not generating a high enough voltage. Which is confusing the ICM. The pickup coil voltage to the ICM increases as the engine RPM increases. I guess it makes sense.
RBob.
As for the misfire, it is likely caused by the pickup coil not generating a high enough voltage. Which is confusing the ICM. The pickup coil voltage to the ICM increases as the engine RPM increases. I guess it makes sense.
RBob.
05-16-2015, 05:22 PM
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Re: TBI with 7749 and $8D S_AUJP
A GM dizzy would be my first suggestion as well.
I have found aftermarket dizzies to be less than good in their reliability and performance.
This is one reason why I use stock dizzies in my engines (when I don't use DIS).
I have found aftermarket dizzies to be less than good in their reliability and performance.
This is one reason why I use stock dizzies in my engines (when I don't use DIS).
05-16-2015, 10:35 PM
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Re: TBI with 7749 and $8D S_AUJP
To be honest, get a GM small cap distributor. They just work. If you find a decent one in the JY and it has an aftermarket ICM, swap the GM ICM you have into it. It has been a bit since I looked but AC Delco distributor shafts are still available.
As for the misfire, it is likely caused by the pickup coil not generating a high enough voltage. Which is confusing the ICM. The pickup coil voltage to the ICM increases as the engine RPM increases. I guess it makes sense.
RBob.
As for the misfire, it is likely caused by the pickup coil not generating a high enough voltage. Which is confusing the ICM. The pickup coil voltage to the ICM increases as the engine RPM increases. I guess it makes sense.
RBob.
I will post a video after it uploads.
The one on the car was from eBay. My friend bought it for this project. I took for granted that it would function for a SBC engine because it was sold as a part for a SBC engine.
They used a 70's Chrysler-style pickup coil with a massive gap between the pole pieces and the pickup coil. Furthermore, the firing was BETWEEN the pole pieces, not at the crossing of the pole pieces. I could have fixed this by changing the pickup coil polarity, but the rotor-to-cap phasing would have been all messed up. So I bought a new OEM style unit. It is not a GM part, but it appears to be made exactly the same.
I feel bad for making a noob mistake like this. I have done several Buick builds, with turbo and speed density conversions, so I believe I know my way around these systems. But I have used DIS on my builds which is a factory plug and play package. Haven't had to deal with this type of crap quality much before. The injectors, ECM, turbo, etc. on my builds was used OEM stuff that I got from the JY and refurbished. This works so much better than the misfit "new" shitt they sell these days.
Sincerely,
David
NOTE: I combined the two videos. Skip to 2:55 to get to the new part.
05-25-2015, 08:26 PM
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Re: TBI with 7749 and $8D S_AUJP
Well - I have got some tuning time in on this beast. And it is a beast. It has the ability to give whiplash at will in most any gear and pulls like a freight train to 5500 RPM. Totally happy with it and will try to make a video of it soon. I am not accustomed to driving a manual tranny car, and can't video and shift at the same time! Will try to rig up a camera mount tomorrow.
One thing I have noticed, this engine is very sensitive to timing. It has a narrow window of timing advance where it will make power. Too little and it has a poppy exhaust note and little power, too much and the same thing happens. I am still working on the timing curve.
Reading up on it I see most people recommend not going above 40° BTDC at WOT. I haven't seen any detonation show up in the datalogs regardless of the timing so I wonder if the detonation sensor is working.
Sincerely,
David
One thing I have noticed, this engine is very sensitive to timing. It has a narrow window of timing advance where it will make power. Too little and it has a poppy exhaust note and little power, too much and the same thing happens. I am still working on the timing curve.
Reading up on it I see most people recommend not going above 40° BTDC at WOT. I haven't seen any detonation show up in the datalogs regardless of the timing so I wonder if the detonation sensor is working.
Sincerely,
David
05-26-2015, 11:38 AM
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Re: TBI with 7749 and $8D S_AUJP
They used a 70's Chrysler-style pickup coil with a massive gap between the pole pieces and the pickup coil. Furthermore, the firing was BETWEEN the pole pieces, not at the crossing of the pole pieces. I could have fixed this by changing the pickup coil polarity, but the rotor-to-cap phasing would have been all messed up. So I bought a new OEM style unit. It is not a GM part, but it appears to be made exactly the same.
The "spark latency" would be different in the ECM program to compensate for the "in between" phasing you were seeing from the pickup to module combination.
Its one of those things you probably could have made work but the direction you went will be best in the long run. Less confusing in the future.
RBob did some testing of the modules years ago to show how they change output with RPM.
If want to dig into the little things deeper it is worth a look to verify you have the "best" numbers in the compensation table for the module.
Here was a discussion on the subject that may "Spark" your imagination.
https://www.thirdgen.org/forums/diy-...n-modules.html
Jp
05-26-2015, 12:18 PM
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Re: TBI with 7749 and $8D S_AUJP
That may have been some type of optical pickup in the Ebay dizzy. Thats why it didn't light the LED like the magnet did.
The "spark latency" would be different in the ECM program to compensate for the "in between" phasing you were seeing from the pickup to module combination.
Its one of those things you probably could have made work but the direction you went will be best in the long run. Less confusing in the future.
RBob did some testing of the modules years ago to show how they change output with RPM.
If want to dig into the little things deeper it is worth a look to verify you have the "best" numbers in the compensation table for the module.
Here was a discussion on the subject that may "Spark" your imagination.
https://www.thirdgen.org/forums/diy-...n-modules.html
Jp
The "spark latency" would be different in the ECM program to compensate for the "in between" phasing you were seeing from the pickup to module combination.
Its one of those things you probably could have made work but the direction you went will be best in the long run. Less confusing in the future.
RBob did some testing of the modules years ago to show how they change output with RPM.
If want to dig into the little things deeper it is worth a look to verify you have the "best" numbers in the compensation table for the module.
Here was a discussion on the subject that may "Spark" your imagination.
https://www.thirdgen.org/forums/diy-...n-modules.html
Jp
I will probably do some testing with timing light and see what sort of mismatch there is between the ECM reported value and the actual value, at speed. I have verified the base timing with the set-timing connector open.
I also verified the timing reported on the ECM matches reality, by comparing digital advance timing light to the TunerPro display. I only did this at 1000 RPM though.
Looks like I may be going on a work assignment for up to a few weeks, so maybe it is a while before I get to it.
05-28-2015, 11:03 PM
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Re: TBI with 7749 and $8D S_AUJP
Today's tuning session revealed why I had the high RPM breakup. In the end, the engine had a developing mechanical problem.
After verifying timing was registering correctly on the laptop in agreement with the real-world at the balancer with the light, I went for one more test drive.
New spark plugs with a smaller gap (0.040 down to 0.030") and cut-back ground electrode really improved the engine! I thought today was the day that it would be finished but no.
The #5 exhaust valve seized in its guide, bent the pushrod, and was bent by the piston. I am pretty sure this was an ongoing problem based on the looks of the valvestem and guide.
So back apart she came and heads to be taken back to the machinist. Very disappointing because the heads both had all new guides installed, and the car was running so well. Oh well.
After verifying timing was registering correctly on the laptop in agreement with the real-world at the balancer with the light, I went for one more test drive.
New spark plugs with a smaller gap (0.040 down to 0.030") and cut-back ground electrode really improved the engine! I thought today was the day that it would be finished but no.
The #5 exhaust valve seized in its guide, bent the pushrod, and was bent by the piston. I am pretty sure this was an ongoing problem based on the looks of the valvestem and guide.
So back apart she came and heads to be taken back to the machinist. Very disappointing because the heads both had all new guides installed, and the car was running so well. Oh well.
05-29-2015, 10:00 PM
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Re: TBI with 7749 and $8D S_AUJP
I started a new thread on the valve guide problem. It's here:
https://www.thirdgen.org/forums/tech...ml#post5922542
https://www.thirdgen.org/forums/tech...ml#post5922542
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