badmoon47

Just joined this forum a few weeks back and it has been GREATLY helpful. I have a 1979 El Camino with a TPI unit from Affordable Fuel Injection installed. It is based on a 1990 Camaro speed density system with the same ECM. I installed it on my 305 about 6 months ago and have been very happy with the swap. It starts right up, idles smoothly at 800 rpm, and accelerates strongly. My problem has been a slight miss at part throttle cruise. My car has the T5 manual tranny and it happens in all gears and at all RPMs particularly below 2000. It is just noticable to be annoying and has been doing this since the install. The car has full length headers, no pollution controls, aluminum Trick Flow heads, and an aftermarket flat tappet cam (206/212 dur 4.35 lift 110 LSA). I have :

- gotten my BLMs all within 125-134 range
- added timing (slight miss turns to significant bucking)
- removed timing (car gets sluggish but still misses)
- replaced coil (Blaster 2)
- replaced plug wires
- replaced plugs (Champion RC9YC)
- new distributor cap
- new rotor
- drove around with each fuel injector unplugged (car runs crappy but still misses)
- installed 2 extra ground straps from heads to frame
- drove with gas cap off in case it was a venting problem

Nothing in my above list made any difference in the miss. If anyone has any ideas, I could use the help. I've been banging my head for 6 months on this one.

THANKS!!!

DuBree 87

Yea I went through tons of hassle for this similar problem and a simple tweak did the trick. If your motor has an EGR valve with a vacuum line, try unhooking and plugging up the line. After my motor was rebuilt, had problems with bucking under acceleration and rough idle at cruising speeds. Now it accelerates much smoother and has no idle glitches.

badmoon47

I guess I should have mentioned, I have no EGR. Thanks for the response though.

mlynch001

What VSS are you using? Are you running a 4000 pulse VSS?

badmoon47

I am not running a VSS. The MEMCAL they sent me was patched to operate without one.

mlynch001

Does they Chip tuner have experience running SD set up without VSS? I know that they say this works, but I find it very hard to believe. Sounds just like a car with a bad or no VSS. The VSS helps the ECU determine mixture and the timing. I am not an expert, but my 91 SD setup on my 85 El Camino did the same thing when I tried to run it without a VSS. If you eliminate the VSS, the timing and mixture cannot be optimized.

Quoting Stealth : "The speed sensors are smog legal for engine swaps, and have been issued CARB EO #D-371. Without a VSS, the Chevrolet Fuel Injected engines will not run correctly, and they will not pass a smog test. Basically, the VSS tells the ECM how fast the vehicle is going. Most people think the VSS is only used for the lock-up torque converter. The VSS is also used to control the EGR valve, the charcoal canister purge valve, the electric cooling fans, idle speed, and air/fuel ratio. This is all explained in the Chevrolet shop manuals.
It must be emphasized that the VSS is used to control the idle speed when the vehicle is moving. Without the VSS, a vehicle may have stalling problems under certain conditions. Needless to say, this is dangerous. Raising the minimum idle speed with the adjusting screw can eliminate stalling, but the engine will still not run optimally without a VSS.
A lot of people think that running "closed loop" is best for fuel mileage. Closed loop simply means that the oxygen sensor is being used to monitor the fuel/air ratio. Some of the Chevrolet fuel-injected engines are programmed to run lean under certain conditions (called "highway mode") to improve fuel mileage during steady cruise conditions. Without a VSS, the engine computer (ECM) will not get the correct signals to run the engine for best fuel mileage. There are a lot of programs in the ECM that depend on the VSS. For best operation, the VSS needs to be connected and functioning."

So, with this chip the car has never run right? You are using a 7730 ECM, right? Have you tried a stock chip? I am running a very similar setup but with a stock ECM, AXXB EPROM, Injection specialties Harness, F body headers (modified to fit), NO emissions (EGR, CATS, AIR, Canister are all MIA), 2 1/2" dual exhaust, etc. My engine has EQ Vortec Hybrid iron heads, L31 Roller cam .440I/.450E 190I/200E @ .050 112 LSA, 1.6 Roller rockers, 9.5 compression, etc. So we are pretty close on setup. My 7730 with an AXXB runs pretty good, considering. But it will not run right w/o a VSS. I keep going back to the chip being "patched" to run without a VSS. I would ask SPECIFICALLY what is the "patch"? You just cannot set the VSS Bin at an arbitrary number, that will not work. It would be a lot easier to use a VSS and know that everything was working right than to "hope" that they thought of EVERY possible conflict when making their patch to the EPROM.

badmoon47

Mlynch001,

Thanks for the reply. I contacted the guy that sent me my original chip and he said the chip is setup to run without a VSS and that the only thing I am losing without it is highway mode. He said he would send me a new chip, a VSS, and the wiring for it for $175. I am thinking about going ahead and getting it just to rule it out as a possible cause. What you wrote makes total sense though and I am curious to see the change in how the car runs. Thanks again for all the info. Good to talk to a fellow Elco owner with TPI. Just curious as to what kind of mileage you are getting from your setup. Mine is my daily driver and I am getting around 18.5 mpg which isn't much better than my old Quadrajet setup. I was hoping for low 20s with TPI. Maybe this has something to do with no VSS.

mlynch001

badmoon47,

It ABSOLUTELY Does! The "highway mode" is where the TPI delivers the best mileage. Without that, the ECM runs in a richer mode. That is why the VSS is so critical! I have not checked my mileage, since I just got it installed and running! I am still working on getting all the other "Minor but Miserable" problems sorted out. I know that the car does not smell rich, even when starting and does not puff black when under a WOT load, so I am betting that the fuel economy must be better. At least, I am not dumping raw gas out the pipes! I will let you know when I get a read on the Mileage. My transmission and rear gear change could affect the mileage, since I went from a 200C and 2.42 gears to a 200-4R and 3.42 gears. I am thinking that this setup should get in the mid 20's if I stay out of the loud pedal!

That Symptom came to my car when I was trying to drive it w/o the VSS. My 85 SS was getting 16-18in town and 20-21 on the road with an electronic Q-Jet. Pretty impressive, but the driveability was not ideal. If the TPI delivers the same mileage and a lot more performance, I will be happy! BTW, my project started over the flywheel loosing a tooth and breaking the starter.

DuBree 87

Of course I missed the no emission part, kinda thought a street legal company would have to sell a motor with emissions so I looked over it. Then again in 79 there was no such thing.

Wow, had no idea the VSS helped control so many things....

NY87Iroc

iTrader: (1)

I had the same problem for 2 years and I replaced the plugs, wires, cap, rotor and pickup coil TWICE and still had a slight miss. I replaced my distributor with a new MSD and MSD 8.5 mm wires and the car runs like brand new.

cal30_sniper

iTrader: (16)

Just another thought. Apparently a lot of people are having problems running the MSD Blaster coils. I've got the same one on my TBI 350 Suburban, and I'm having the same problems as you. I'll be pulling it off ASAP to see if that's the problem. I'll let you know.

-Levi

badmoon47

Sniper,

That would be an easy fix AND a big relief! Let me know if the swap helps.

badmoon47

I bought a reman distributor at AutoZone today and installed it. The car started instantly. It has always taken 2-3 seconds of cranking before it started. I found this interesting. I took the car for a quick drive around the neighborhood and it seemed much better. Its not perfect (I still felt a miss or two holding low speeds), but it seemed much smoother. I will have time to take it for a "real" drive tomorrow and let you know what I find. Fingers are crossed.

badmoon47

Nope. Miss is still there. Really had my hopes up on that one. Affordable Fuel Injection said the injectors are under warranty and are sending me a new set next week. They are the only thing I have not replaced. I'll let you know.

badmoon47

Got a "check engine" light the other day. Came on during steady state highway cruising. Came on for 2 minutes or so and then went away. Has not returned. The car ran no differently when it was on than when it was off. When I got home, I hooked it up to DataMaster and it showed a Code 45 "O2 RICH". I pulled a plug from both sides of the engine and they were chalky white. To me, this would indicate a lean condition and not a rich one. I'm pretty sure this Code 45 has to be related to the miss I have been having. Could a bad injector be the culprit and throw a rich code while still running lean? Any input appreciated.

badmoon47

Replaced all 8 injectors today and the car runs the same. Still has a misfire at part throttle. I am totally out of ideas. Anyone?

cal30_sniper

iTrader: (16)

Go back to the factory coil. I had the blaster coil in my Suburban, and it had the same part throttle miss you're describing. It caused a nasty bucking when the torque converter was engaged. I didn't replace the entire distributor, just the ignition module, and I noticed the same partial fix to the problem that you did. The next step, which solved almost all the problem, was replacing the ignition coil. I tried an MSD Blaster, an Accel High Output Unit, and an old GM unit I had laying around in the trunk. The Accel made it drivable on the highway, the old GM unit ran like total dog mess with awful stumbling at part throttle, and the MSD was somewhere in-between. Last weekend I replaced the Accel coil with a brand new AC Delco unit from Summit Racing. Immediately, it solved about 90% of the missing problem. I can now hold 75mph up a grade in fourth gear with the converter locked up without stumbling (and that's in a 5500 lb Suburban, should be much better in yours). I can also accelerate to pass, etc, without stumbling and without unlocking the torque converter (I have a manual switch I wired in so I could unlock the converter to keep it from stumbling so bad up a grade or under slight acceleration). I have a feeling the other 10% of my stumbling problem that is left is coming from somewhere in the distributor, it's the original unit with about 280k on it now. I have a feeling as soon as I replace that I won't have an issue at all.

Long story short, replace your coil. Go with the OEM unit, stay away from the high output stuff, and you should be just fine.

As a side note, the reason your vehicle starts so much better now is due to the new ignition module that was likely put in the remanufactured distributor. Eventually, they can get so bad that the car won't start at all. Or, you can put in a brand new Accel Ignition Module and have it be bad from the factory. That's what happened to me. Live and learn, just stick with the OEM parts for a driver would be my suggestion.

badmoon47

Put a new OEM coil in today. No difference. I am beginning to think there is something wrong with the engine itself. Maybe the valves need re-adjustment?

cal30_sniper

iTrader: (16)

No, I can't think of anything internal to the engine that would cause that problem. The valves are self-adjusting for the most part through the hydraulic lifters. If you had a valve adjustment problem, you're lifters would either be clattering like crazy (too loose), or you would have bad vacuum (too tight, causing the valves to stay open).

It's going to be somewhere in the fuel/ignition system. The only thing you haven't replaced that could possibly be a problem that I see is the TPS. It's a long shot, but I have heard of cars with a bad TPS doing stuff like this. I saved that for last, because the silly thing is almost 90 bucks to get the OEM replacement part.

Other than that, my bet would be there is something screwed up in your computer coding somewhere. Something with that chip just isn't right. Perhaps you could try having another one burned, or get the stuff to open it up yourself and take a look?

I understand your frustration. Like I said, I've been dealing with the same problem in my DD for almost a year.

badmoon47

That's true about the valve adjustment. I think I was grasping at straws. The car is quiet, idles great and has plenty of power. I have been burning chips left and right and no matter what changes I make, the problem still exists. The TPS shows a nice smooth progression from 0 to 100% on the datalogs, but you never know it might be worth a shot.

cal30_sniper

iTrader: (16)

Hmmm... Only other thing I've been able to think of all day is the plug gap. What are you running them at? Also, I'm not sure what plugs exactly are required for those Trick Flow heads, but they're likely not in the same heat range as the plugs used in the factory cast iron heads. Are the plugs you're using set up for use in aluminum heads with compression ratio you're running in that 305? I know I had to do a bit of mix matching to get plugs that worked well with the 113 aluminum heads I put on my 305 'bird.

Just some more to chew on.

badmoon47

I am using RC9YCs right out of the box. Since they are not for a stock application, I just took them right out of the box and installed them. Not sure of the heat range, but I think they are on the cold side. I will check to see if Trick Flow recommends anything in particular.

mlynch001

Since you have eliminated all the "EASY" stuff, we are officially looking for the "needle in a haystack" so, here are some other possibilities:

Is it possible that your headers are "tricking" the O2 Sensor by "over scavenging"? Your problem sounds just like "lean surge" on a carbureted engine. It is very possible for the tuning of the headers to actually "pull" or "suck" the charge out of the cylinders and into the pipes before the exhaust valve closes. What that would give you is a cylinder with too little fuel (lean) and a header with a slug of unburned fuel/air mix (rich) in the header. This might be happening only at a certain resonance point or RPM. The TPI system will be at its' very leanest at light throttle cruise and if this corresponds with a resonance the two could combine to make one or more the cylinders lean and the exhaust rich. With the restrictive OEM exhaust manifolds and system, this is NEVER a problem, but with a free flowing system, the scavenging effect is more pronounced.

Where is the O2 sensor located? May be too far from the exhaust ports to be accurate? Remember that the OEM location of the sensor was very close to the exhaust ports on the OEM Iron manifolds. Have you checked to see if the ECM is going into "Closed loop" operation? Have you tried to unplug the O2 sensor and force the ECM into "open loop"? Open loop is a slightly richer mode and might help you isolate the problem. Unplugging the O2 sensor will set Code 13 and cause the ECM to default to Open loop operation.

I doubt plug heat range just does not match the symptoms. Too "hot" on the plugs and you would be getting pre-ignition knock and too "cold" the plugs would be fouled. On very mild engines (such as yours and mine), I just do not see the plug heat range as that critical, for what that is worth.

badmoon47

Lynch,

Thanks for the reply. It definitely feels like a lean miss. I had an underjetted carb once that had the same symptoms. Those symptoms went away with bigger jets installed. The chalky white plugs and Code 45 "RICH O2" would go with what you said. I have a heated O2 sensor that is in the passenger side header collector as per the install instructions. The ECM is going into closed loop and stays there through all of my datalogs. If the headers are scavenging, is there a way to tune for this? I have not tried unplugging the O2 sensor, but it is worth a shot. I will try when I get back in town and let you know.

badmoon47

I did a few test drives with the O2 sensor unplugged and it made no difference. I then added a bunch of fuel to my VE tables but the miss remained. I guess it is not a lean miss after all. I re-connected the O2 sensor and got another "Code 45 O2 Rich" on the way to work. As soon as I let off the gas pedal it went away and did not return. I removed a couple of plugs when I got home and they were both grayish white. I am running out of ideas!

rgarcia63

I had the stumbling/miss because my headers were causing the O2 to experience a large delta T (cooling off too much.) This was solved by adapting a heated O2.
If you have headers a heated O2 is a good mod even if you don't have a miss.

badmoon47

I installed a heated O2 sensor when I swapped oer to TPI. Thanks though.

mlynch001

What kind of fuel are you running? Have you pulled ALL the plugs? Do they ALL look the same color?

One thing that I see is Champion plugs, I have an aversion to Champion plugs, I had two sets that gave a misfire problem and Set a misfire Code on my wifes' Dodge Caravan so I went to my old standby, Bosch Platinum Plus and the problem went away. I had issues with Champion plugs in my Honda motorcycles as well (years ago) so I do not "do" Champion plugs, but that is just me! I do NGK and BOSCH, nothing else. I read on another website that that RC9YC was a much colder plug than the FR3LS AC that Trick Flow recommends. I think that the FR3LS AC crosses to a RC12YC, so a RC9YC is a lot colder plug! I think that this states that the RC9YC has been replaced by a RC9YC4 which is designed to gap at .040-.045, where the 9YC is a .030-.035 design gap plug. HEI ignition really DEMAND .045 or greater gaps. Early HEI's used .060-.080 gaps!

http://www.chevelles.com/forums/showthread.php?t=33913

What plug gap are you running? Are these "projected core" plugs? I would run Bosch or NGK projected core, resistor plugs at .045 or greater gap. That is what I am using.

badmoon47

All 8 plugs look similar. A chalky white tip with a brownish black ring. I guess I could try a hotter and different plug type. I will let you know.

mlynch001

The Ceramic insulator is brownish black? When reading plugs, you need to look at the color of the insulator, not the electrode. How about a picture of the plug(s)? Just want to make sure that you and I are "reading" the same plug.

A couple of things to remember with Late model cars and unleaded fuel, Plug color takes a long time to develop and can be very deceptive. If you have "a brownish black" insulator, then you are likely VERY Rich and fouling the plugs. "Brownish black" deposits on the insulator would contain a lot of carbon content and could likely cause the spark current to divert to ground instead of jumping the gap. You are looking for a light tan insulator with almost none or no dark deposits at all.

See this link for some helpful information on reading plugs.

http://www.ngksparkplugs.com/tech_su...qs/faqread.asp

Do not get me wrong, NOT saying you are not getting the plug reading right, but we are BOTH missing something here! This cannot be as difficult as it seems to find this issue.

Thanks!

NY87Iroc

iTrader: (1)

Having E10 gas does not make it any easier to read plugs either..just had to throw my 2 cents in.

badmoon47

I guess I didn't describe the plugs very well. The brownish black is on the metal base of the plug (the ring around the insulator). The electrode is grayish white and the insulator is completely white. I would post pictures, but I am technically challenged in the digital photo department. Hope this helps and thanks again for all the responses.

mlynch001

Yes, E-10 and E-85 are a major problem in so many ways!

Unleaded gasoline colors so slowly as it is and when you throw in the extra detergents and what not, you have a real issue reading plugs that have run only for a short time.

Plus the fact that we are all paying taxes for subsidies to all the Ethanol producers to make the crap that decreases the performance of our vehicles.