** I am posting this hear as I realized there is a forum specific to TPI problems. I hope this was okay.

I have been chasing a funky problem for awhile now. Basically, when I get above half throttle my truck starts to pop like its misfiring or going lean. Now, if I really get on it in first gear it does it the most. If I am only going 30mph and in 3rd gear, and I floor it, it doesn't pop, but doesn't have much pep (partly due to the low speed and 1:1 ratio of the gear). It seems the higher the RPM or more the load, the more the popping. This makes me think its going lean.

My combo is this: 350 with a TPI. Custom chip (via me), painless harness. Th-350 trans, 4.10 gears. If you request any more info I'll be happy to provide.

As I work for a parts house (at least when I am not in school), I can replace things cheaply if not for free. Before I began parts replacement I checked the basics like base timing (set at 6 degrees) and fuel pressure (currently at 40PSI).

Over time, pretty much EVERYTHING has been replaced. When it first began doing this I replaced the fuel pump and filter. No change. I then checked and replaced the fuel pressure regulator diaphram. No change. At that point I though that it might be going lean due to inaccurate air readings. I swapped in a friends good MAF and there was no change.

My spark appeared to be a bit weak so I put in a new coil and module and a wireset and while the spark looked a bit more powerful, the same problem was occuring.

At that point I decided to toss in a new computer and MAF power relay.. After that the truck ran GREAT! So I drove it down to school and within a few days it began acting up again. As it was free, I tossed in a new ECU and there was no change. As it was seeming to act up at a certain throttle point, I though my TPS might have a flat spot. I couldn't see one through my scanner but I decided to put in a new TPS anyways. After that, the truck ran GREAT!

Two days later, same problem occuring. I really have no idea what it could be. It seems to get better after random parts replacement. I also changed out the oxygen sensor as it was time. The idle smoothed a bit but the main problem persisted.

I am about ready to ditch the whole ECU system and go with an aftermarket unit. Before I drop that sort of money, does anyone have any ideas?

Thanks for your help.

Also, what are the part numbers for the MAF Power and Burn-off relays. I have searched this board but have found conflicting results as to if these are interchangeable. Some people say they are totally interchangable, others say no they aren't. Any definitive answer? I believe my power relay is currently an MR22. However the listed part number now appears to be MR82. Could this be the sourse of my problem?


Last edited by siggy_freud on 10-12-2005 at 10:58 PM

 

I was wondering if you have the original injectors in it yet? If so and even if not check the resistance on all the injectors when the engine is warm. Most of the tpi units ran on what is called bank fire. The ecm fires a bank or batch of injectors at once and if one is bad and shorts out none of the injectors will fire on that bank. Wich would give you a lean running condition. If all the injectors check out good let me know and I will see if I might be able to come up with some more ideas.

 

After you changed the oxygen sensor, did you unplug/reset the ECU?

Did you check fuel pressure while the problem is happening?

I'm not sure about the relays.

 

The computer has been reset. I have checked the fuel pressure before and after the problem and it remains the same. I dont really have a way of checking it while I drive.

Also, I noticed that the part numbers for an 85 and 86 MAF are different. I have been running an 85 MAF for some time now. What is their differences and could this be the culprit?

 

sometimes your fuel pump can act up only while your car is acting up. check ing module and when you adjust the timing and you are turning the distributer to the left and right is there a delay in the timing change if so it could be your timing chain. If I bought a third gen today. These would be the first two things I would replace along with tune up items and o2 sensor

 

The timing seems to respond nicely. The chain is only about 6 months old. The fuel pump is also only few months old and has actually been replaced twice just to be sure.

Thanks for the suggestions all.

 

I'm currently fighting the same type of issue. I just put a vortec headed 355 in a Tahoe. It's run rich at idle(black blowing out tail pipes) and pops and stumbles at around 2/3 throttle(around 4,000). The stumble acts like a lean situtation, but its rich as hell at idle. I've played w/ timing, TPS, new acdelco fuel pump, checked the press. reg, new plugs/wires, new cap/rotor, re-set valves. I'm lost. It seems to run smooth, fires instantly, but has this "stumble". - any thoughts?

- I'm going to try another ign module in the morning, and check injector ohms.

 

siggy_freud - any news?

 

what about the prom