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Car runs great (after some hair pulling) down the road and has plenty of power for a few minutes of driving even when the engine has reached 210 ish and the fan is on.
Due to the previous issues to get the car running I have replaced the distributor cap and rotor, spark plug wires, spark plugs, fuel injectors (southbay), and fuel pressure regulator.
Now after 15 - 20 mins of driving the car starts to hesitate and stumble under light throttle and bogs out. It takes a couple minutes and sometimes it will return to normal. Also after this behind it will stall when coming to a complete stop/ on take off. I let the car sit about 2 hours and then it ran fine again which is leading me to think it is a heat soaking issue of some kind but would like to know what you guys think before I begin spending more money
Re: 86 tpi bogs and stumbles after driving when hot
When things like this occur, having a scanner to look at data can be a big help. Without it, often time we just start throwing parts at the car in a process of elimination (which, yeah, can be very expensive).
This could be any number of things... bad sensor, fuel system issue, etc...
Any chance you could get access to a scanner? Sometimes the local parts stores (like Autozone) have loan-a-tool programs...
Re: 86 tpi bogs and stumbles after driving when hot
The local stores don't have anything to rent that will scan and show data on the OBD1. I have tunerprort a d an aldl cable that I am going to try using when it acts up again but unfortunately I'm not sure if I will be able to see much from the sensors. If the coil or module is acting up in not sure that would show up in tunerpro.
Re: 86 tpi bogs and stumbles after driving when hot
Originally Posted by 2012sergen11
Car runs great (after some hair pulling) down the road and has plenty of power for a few minutes of driving even when the engine has reached 210 ish and the fan is on.
Due to the previous issues to get the car running I have replaced the distributor cap and rotor, spark plug wires, spark plugs, fuel injectors (southbay), and fuel pressure regulator.
Now after 15 - 20 mins of driving the car starts to hesitate and stumble under light throttle and bogs out. It takes a couple minutes and sometimes it will return to normal. Also after this behind it will stall when coming to a complete stop/ on take off. I let the car sit about 2 hours and then it ran fine again which is leading me to think it is a heat soaking issue of some kind but would like to know what you guys think before I begin spending more money
It has been my experience that the newer Bosch injectors do not work well in GM EFI systems without tuning modifications to the injector tables.
Re: 86 tpi bogs and stumbles after driving when hot
Oooooo.... he has Bosch-III's. I didn't catch that part...
Uh oh... yeah, yours and numerous other people's experience with those things have been he same... needing tuning to get them to run properly.
I really think these injector companies need to include a caution note on their websites about possibly needing tuning to run these Bosch-III's. Evidently they are often NOT drop in replacements.
Any rate, back to the OP...
Notwithstanding the Bosch-III injector thing... It takes some deductive reasoning, but sometimes you can trace problems to malfunctioning parts that the computer can’t see (like ignition coils or fuel filters) by looking at what the computer is doing with the fuel trim (are you lean? Rich? At what operating condition? Etc…). BTW, I’ve also had issues where the computer noted a trouble code but the SES light didn’t come on.
If you have Tunerpro I’d highly recommend trying to get it going so you get visibility on the operational data before attempting to make any more repairs.
Re: 86 tpi bogs and stumbles after driving when hot
You mentioned that "Due to the previous issues to get the car running..." I will assume the car was not running properly when you started your work.
The best thing to do in circumstances like this is to change one thing at a time and noting any improvement or worsening. In my experience, sometimes changing more than one thing can introduce a new problem that did not exist before which makes solving your problems way more difficult. This is not the case for a preventative tune-up. If a car was running fine before the tune-up, it should run fine after and if it doesn't it is something that was worked on.
There is controversy over the Bosch D3s. If your car was running fine with them at some point in time before then leave them in there for now.
I had a similar issue with a warming issue. Turns out I poorly routed my spark wires and my new Taylors eventually baked against the side of the exhaust manifold and shorted out. The symptoms (rough idle, stumble, and high RPM misfire) were less when the car was cold, then, after heat up it would get worse.
Two things I would do first:
1. Check the vacuum at idle. This will eliminate any vacuum issues.
2. Once the engine starts to stumble, in the dark, (no lights) open the hood and observe the spark plug wires from the cap to the plug area (this can all be done from the top). Rev the engine as you do. You will see flashes in the dark at the spot the spark wires may be broken meaning they are shorting out before they get to the spark plug and causing misfire.
Re: 86 tpi bogs and stumbles after driving when hot
1. What vacuum should I see at idle for the stock 305?
2. The routing of my wires is not great, they are a bit short to get around the AIR tubes and stuff so I'll definitely look for burnt thru wires. Has anyone found a set of wires for these engines that fit well?
Re: 86 tpi bogs and stumbles after driving when hot
Vacuum should be 20 inches or so.
The Taylor 51006 fits really well. Plenty of length to route.
I recently put in the Delco 9708S wires that are supposedly made for my engine. The Delcos snap onto the plugs a lot more easily and affirmatively than the Taylors but the Taylors are clearly heavier duty. And even though the Delcos are cut to length and they come with 3 straight boots, there is no guidance as to which is for which cylinder which is dumb. They should at least give us that.
Proper routing on these cars is tough. The engine bay is cramped and there are sensitive sensor wires running near the spark wires. I needed to be very careful to keep both the spark wires and sensor wires away from each other and the manifolds.
IMHO, I think these cars would do best with straight boots on all except cylinder 7.
Last edited by Tootie Pang; 09-18-2017 at 12:29 PM.
Re: 86 tpi bogs and stumbles after driving when hot
Originally Posted by 2012sergen11
I forgot to mention that I have a chip with tuning to the voltage offset tables that should accommodate the Bosch 3's
Where did the offsets come from? If they're not specific to your injector p/n, it could still be problematic.
Also, did you zero out the low PW correction table? That and the voltage offsets are the two things you need to do with Bosch-III's besides potentially a minor tweak to the flow rate value.
Re: 86 tpi bogs and stumbles after driving when hot
Originally Posted by ULTM8Z
Where did the offsets come from? If they're not specific to your injector p/n, it could still be problematic.
Also, did you zero out the low PW correction table? That and the voltage offsets are the two things you need to do with Bosch-III's besides potentially a minor tweak to the flow rate value.
I believe the tuning to be correct for the 19 lb injectors, the chip I have was made by Tuned Performance here on the site.
Re: 86 tpi bogs and stumbles after driving when hot
Im not sure what the pn for the 19#hr injectors.
Iirc the Bosch 3 22#hr are 0280155710 .
I found the offsets from a thread bye rbob I can't recall the injector pn so they maybe off.
He does have a few other proms to see if it effects the running.
I believe I used these settings
Originally Posted by RBob
From what I've found on the 'net the 280-155-700 injector is a 19#/hr. But that is with a substitute liquid (not gasoline).
I'm not sure if I used the correct data sheet. As the 280-155-700 is a Bosch number which Ford doesn't use. I used the Ford 19 #/hr data.
With that here is the data for the injector at 44 psi, values in mSec:
Re: 86 tpi bogs and stumbles after driving when hot
Would the offsets being slightly off cause an issue like this only when the engine has been run for a while and is hot? When the engine is cold it runs very well and has good throttle response
Re: 86 tpi bogs and stumbles after driving when hot
Originally Posted by 2012sergen11
Would the offsets being slightly off cause an issue like this only when the engine has been run for a while and is hot? When the engine is cold it runs very well and has good throttle response
Can depend on if you're in closed or open loop when "cold".
Re: 86 tpi bogs and stumbles after driving when hot
I will get the injector part number tonight. I plan on running the car with my laptop hooked up so maybe I can see if one of the sensors starts going erratic when the car gets hot. I drove it a bit last nite and the issue is pretty intermittent. Sometimes it will have me hiccups and then continue running better for a bit and other times it gets so bad it will barely keep running
Re: 86 tpi bogs and stumbles after driving when hot
Yup adding that to the list of to-dos later as well as anything you guys can suggest to check other sensors that would cause an intermittent issue like this
Re: 86 tpi bogs and stumbles after driving when hot
Originally Posted by 2012sergen11
Yup adding that to the list of to-dos later as well as anything you guys can suggest to check other sensors that would cause an intermittent issue like this
One thing I ran across on several of these MAF cars is a bad MAF sensor that acts intermittent. What I have found is if you have the engine running, lightly tap on the housing with the handle end of a screw driver. If the engine stumbles or stalls it has a bad MAF. The OEM Bosch MAFs were terrible when new, much less now 30+ years later.
I have seen the tap test mentioned on many of the 80s GM models with the same style Bosch Hotwire MAF.
Re: 86 tpi bogs and stumbles after driving when hot
Okay so the injector part number as best as I can read it is 0280155887.
I took a short datalog of the car idling in the driveway as well as reving the engine a bit to see how everything re acted. In the log I am getting an 'error' down in the engine code list for code 43, ESC
Re: 86 tpi bogs and stumbles after driving when hot
Based on what I can find here on the site it sounds like o need to check my connection to the knock sensor, the sensor itself, or the module on the firewall. The first thing I am going to look at is the connector, there were some melted connectors on the car when I got it that needed repaired so there's a chance the connector is no good down there.
What type of timing advance should I be seeing with the pretty stock tune? I'd like to know what I should see so that I can datalog the car and see if the computer is still pulling timing in "safe mode" or not
Re: 86 tpi bogs and stumbles after driving when hot
I was able to drive the car this evening and log a bit of data as I test drove a bit. Once the car was running in closed loop it seems like there is a spark advance issue. (maybe?) Under partial throttle (<1 V TPS) I get plenty of driveability and timing is up in the low 30's (rel. to TDC) but when I get in the pedal the timing drops wayyyyyy down and pegs just below 20 (rel. to TDC).
Here is a snapshot of my log where I get into the pedal and it is bogging out. You can see the total timing, timing the computer is adding to the base timing, KS retard, KS counts, RPM, and TPS
I fixed the connector on the KS to remove any chance of a bad connection but I would assume if the KS itself was causing an issue then the 'knock retard' wouldn't be 0 degrees?
Re: 86 tpi bogs and stumbles after driving when hot
Okay, so at the snapshot above my Load Variable is 166. according to the chart that would put the timing in the 20-22 range if the load variable is correct so I guess the timing may not be as bad as I thought.
Re: 86 tpi bogs and stumbles after driving when hot
Maybe you're not getting into Power Enrichment? Is there a BLM Learn Enable flag available in TP for your mask? Maybe keep an eye on that as you lay into the throttle (or go back and look at recorded data). On $8D, the flag will switch to "disable"' when I hit PE, indicating the ECM is no longer responding to the O2 sensor. Maybe something analagous exists for the MAF cars.
IF it's anything like $8D, there should be a power enrichment spark advance table. For whatever reason, GM didn't put all the timing in the main spark map on $8D. They put 5-7 deg of the total timing into this other table that only gets accessed at WOT.
THe other thing is without going into PE, you'll remain in closed loop and the ECM will attempt to keep you at 14.7:1 rather than letting you get down into the 11-12:1 range. That will DEFINITELY kill off power.
On a MAF car, I don't know what parameters the ECM looks at to determine PE mode... on a MAP car, you need TPS and MAP to hit certain values.
Re: 86 tpi bogs and stumbles after driving when hot
Originally Posted by 2012sergen11
Okay, so at the snapshot above my Load Variable is 166. according to the chart that would put the timing in the 20-22 range if the load variable is correct so I guess the timing may not be as bad as I thought.
Your timing could still be off. The Initial timing at the distributor could be off. The harmonic balancer outer ring could have potentially slipped as well or it could be the wrong one.
I would verify the base timing with the timing wire disconnected to be at 6* BTDC. MANY people forget or simply do not know to unplug the timing wire when they attempt to set the timing. If you have a dial back light, once you shut off the engine, plug back in the timing connector, reset the ECM by removing the negative cable, and restart the engine you should see about 20* of timing at idle and it should rise as you rev the engine under no load. From the timing map above at 2,500-3,000 rpm and no load you should see 38* advance.
Re: 86 tpi bogs and stumbles after driving when hot
Originally Posted by ULTM8Z
Maybe you're not getting into Power Enrichment? Is there a BLM Learn Enable flag available in TP for your mask? Maybe keep an eye on that as you lay into the throttle (or go back and look at recorded data). On $8D, the flag will switch to "disable"' when I hit PE, indicating the ECM is no longer responding to the O2 sensor. Maybe something analagous exists for the MAF cars.
IF it's anything like $8D, there should be a power enrichment spark advance table. For whatever reason, GM didn't put all the timing in the main spark map on $8D. They put 5-7 deg of the total timing into this other table that only gets accessed at WOT.
THe other thing is without going into PE, you'll remain in closed loop and the ECM will attempt to keep you at 14.7:1 rather than letting you get down into the 11-12:1 range. That will DEFINITELY kill off power.
On a MAF car, I don't know what parameters the ECM looks at to determine PE mode... on a MAP car, you need TPS and MAP to hit certain values.
The 305 cars especially MAF cars do not have as much PE timing programmed into them as the 350s do. Usually only 2-4* added.
IIRC the MAF cars use a minimum LV8 and TPS to enter PE.
Re: 86 tpi bogs and stumbles after driving when hot
Originally Posted by Fast355
One thing I ran across on several of these MAF cars is a bad MAF sensor that acts intermittent. What I have found is if you have the engine running, lightly tap on the housing with the handle end of a screw driver. If the engine stumbles or stalls it has a bad MAF. The OEM Bosch MAFs were terrible when new, much less now 30+ years later.
I have seen the tap test mentioned on many of the 80s GM models with the same style Bosch Hotwire MAF.
FINALLY...DID YOU EVER TEST THE MAF THE WAY I DESCRIBED???
If the engine even has the slightest stumble when you are tapping on the MAF it is defective and needs to be replaced.
Re: 86 tpi bogs and stumbles after driving when hot
I have not yet checked the MAF but I plan on doing that next.
The 2.37 V is when I am in the pedal but not to the floor, there's a lot of resistance to the pedal when it is bogging out. In neutral I put the accelerator all the way down and the TPS was reading 4 V
Re: 86 tpi bogs and stumbles after driving when hot
I drove the car while watching the MAF readings until the car started acting up again, the readings were holding steady while the engine bogged and stuttered. The readings were around 120 or 130 ish.
After I got back I tapped on the maf sensor as described above and the idle stayed smooth with no change
Re: 86 tpi bogs and stumbles after driving when hot
Drove the car a bit today after setting the base timing to 6 degrees because it was a bit off. No real improvement. I test drive the car for 15 mins and it ran pretty good but then I went to drive it a few mins later and it barely made it out of the driveway and turn around to go back.
Issue definitely is erratic once the car is hot and I cannot see much in tunerpro that doesn't look right.
Re: 86 tpi bogs and stumbles after driving when hot
Originally Posted by Tuned Performance
Wondering if it's the icm or pu coil breaking down when warm just a thought.
ICM was my initial thought since I know they are problematic but I wanted to eliminate some other causes before buying anything. After the suggestions and tests from others in the thread I think I am at the point of getting an ICM and seeing if that is the problem since it is likely the original one in the car. The only other ICM problem I've had was a no start condition
Re: 86 tpi bogs and stumbles after driving when hot
Did you rev the engine in the dark? Sometimes the higher spark energy brings out the fireflies.
Your injectors, according to WitchHunterPerformance.com tests flows 194cc which, using 95% converstion, is 18.24 lbs which is a little on the light side but that wouldn't cause your problem.
Re: 86 tpi bogs and stumbles after driving when hot
I changed the ICM earlier today, before the comments to do the coil first but now if I need to do the coil it should be quick and easy. I'm going to drive the car tomorrow evening after work but it starts and runs just fine so the ICM wasn't DOA at least
Re: 86 tpi bogs and stumbles after driving when hot
Be careful. Unless you don't mind potentially spending some money on this, just realize you are heading down a "change it, see if that's it, no? change another"... process which can add up.
I think at this point, with your problem consistently emerging after 15 minutes of driving, this is definitively heat related. Have you checked what your INTs and BLMs are doing?
Last edited by Tootie Pang; 09-24-2017 at 07:52 PM.
Re: 86 tpi bogs and stumbles after driving when hot
Originally Posted by Tootie Pang
Be careful. Unless you don't mind potentially spending some money on this, just realize you are heading down a "change it, see if that's it, no? change another"... process which can add up.
I think at this point, with your problem consistently emerging after 15 minutes of driving, this is definitively heat related. Have you checked what your INTs and BLMs are doing?
I agree on changing parts to see if it helps which is why I've been trying to eliminate some possibilities (TPS, MAF) before throwing parts at the car. I feel ok with replacing the ICM and if needed the coil especially since the coil is more "tune-up" related as well. Also I thinknthese are 2 of the most likely culprits of a part heating up and causing problems.
As far as the INTs and BLMs, what should I be looking to see if it continues to act up? Still learning about tuning/datalogging, I have read a bit about these 2 but haven't really learned enough to watch and understand them yet.
Re: 86 tpi bogs and stumbles after driving when hot
If you're misfiring at WOT, nothing in the datastream will tell you anything.
ECM is not in closed loop and the O2 sensor is not capable of reporting an actual AFR.
Only thing i can think of....If say, you're not getting into Power Enrichment mode, you'd see the BLM Learn not go into disabled state. At WOT, the ECM would still be trying to maintain 14.7 AFR, and possibly resulting in a lean enough condition to generate lean misfire.
That's if it's not related to the ignition system of course...
Re: 86 tpi bogs and stumbles after driving when hot
INTs and BLMs are the ECM's adjustments to the injector pulse width (which I believe is in milliseconds) to keep the engine in perfect stoic fuel/air burn condition. The ECM uses rich/stoic/lean from the oxygen sensor to make these adjustments. If the oxygen sensor tells the ECM that the burn is going rich, the INTs go down (shorter) pulse width to put in a little less fuel. If the oxygen sensor still sees rich, the INT's go down some more. This will continue until the oxygen sensor reports "all good" (stoic) or the ECM runs out of adjustment. The BLMs record where the INTs go in a table. The BLMs are several tables that capture the INT's the ECM had to use to bring that particular engine into stoic. These tables are for different engine conditions- idle, part throttle, RPM ranges, etc. These tables are needed so that the ECM already knows the injector widths for the various engine conditions so the engine will already be tuned. Another way to think about it is the INTs are the ECM tuning the engine, the BLMs are the notes that takes and uses from then on. The ideal INT and BLM values are 128. Max is 160, low end I'm not sure. If your BLM's are within the low end and 160, your engine is stoic and is running fine. If the BLMs are withing a specific range around 128 (118-130 I think), this means that the ECM has not had to adjust the fuel amounts more than normal and your engine is running normally.
If the BLMs are beyond this but less than the limits (say 145 out of 160), your engine is still running stoic, but the ECM says it has had to adjust the the fuel beyond what it thinks a normally running engine should be and is an indicator of maybe something that needs fixing.
Let's say you have a brand new, perfectly working stock TPI. The ECM has built in fuel injector pulse width tables from Chevy engineering that starts it off. The tables, and the formula the ECM uses to calculate the pulse width is put together in the ECM programming. This formula use fixed numbers (constants) for engine size, volumetric efficiency, injector rating, etc again based on a properly running stock engine. If you all of the sudden drop in 30 lb injectors, the tables will be off (since they were setup using 19lb) and the ECM will see rich from the oxygen sensor, lower the INTs to shorten the injector pulse widths to compensate but it will eventually hit the lower limit and the oxygen sensor will still see rich. A prom code changing the built in tables will start the ECM off at the correct amount for the 30lb injectors and should keep the INTs and BLM's near 128. This is a "tune".
INT's and BLMs are only used in closed loop (means the oxygen sensor is used for rich/stoic/lean feedback to the ECM). Open loop means the ECM is using built-in table values, no feedback, no "loopback".
Last edited by Tootie Pang; 09-25-2017 at 10:41 AM.
09-18-2017, 07:33 AM
