I am having trouble getting my truck to run right and I was hoping you guys can help. I know I should be trying to burn my own proms, but I just do not have the time to learn all that right now. I have read and read the DIY prom board, it that is going to have to be a hobby in itself.

I have a 92 gmc truck with the 16146299 ECM. I bought the truck with a blown motor, so I don't know how it acted before. I put a .060 350 in it with pro action torquer heads with 1.94 1.5 vavles. The compression is 8.9:1. It has a hyd roller with 202 207 @.050 .420 .420 lift on a 115 lobe sep. I am running a performer intake with an adapter. I did the ultimate tbi mods. I tried an injector spacer, but it was real noisy at idle so I took it out. Still have manifolds, but the cat is gone and I have a 3" in dual 2 1/2 out flowmaster muffler. I also installed a tpi pump. Fuel pressure is at 14 psi. Injectors are stock 350. I have the 3 wire o2 sensor. Right now I have a tbi chips stage 2 chip in it with 0* timing. I am not opposed to going back with the stock one if someone knows how to make it work.

It runs good putting around, but when you put it to the floor, it stumbles on gear changes. And if you are trying to accelerate up a hill at more than 1/2 throttle it sputters and quits gaining rpm. It doesn't do it all the time. I can never seem to get it to do it when I have a meter across the o2 sensor leads. On normal operation, the full throttle o2 volts are .780-.850 kind of depends on the day. On normal driving, the o2 volts go real low (.100-.300) if you have to roll into the gas to get up a steep hill. The volts come back up to .450 after a couple of seconds of steady throttle.

Anyone have any ideas on what I can do to make this a little more drivable?
Thanks
Lynn

 

What did you mean by it made noise when you put the injector spacer on??????

 

Sounds like the classic accel enrich/decel enlean issues. There are two options:

1) Use a heated stock TBI manifold

2) Use an open element, and tune the engine so it runs ok warm with the current manifold.

With the current manifold, you can tune it to run ok most of the time. The problem originates from the fact that the fuel can settle out in the manifold plenum when its cool due to fuel dynamics. Basically instead of going into the motor, the fuel comes out of suspention and wets the manifold walls. This causes a lean tip-in issue wich can cause the engine to hesistate. If its bad enough, itll actually cause the engine to die. When the pressure in the manifold stablizes, the fuel evaporates and goes back into the intake charge, causing the engine to go rich, which can then cause it to stumble.

This effect is also dependant on temperature, so you wont be able to fix it completly, just fix it enough so that its not a major nusance issue like it is now.

Basically, the way you fix it is to edit the MAP or TPS AE pulsewidth, depending on how your ECM is layed out, to provide enough fuel to compensate for what the manifold is hanging onto when you hit the gas. The effect is primarily based on MAP, so if possible use that, but the TPS AE is OK if thats what the ECM is set up to use primarily. After that youll want to tweak with the decel enlean. This wont fix all your issues, but at least itll help remedy the stumble and hesitation to a good extent.

Be thankful you dont have a stick. I actually had to custom program my own model to provide the correct ammount of AE using the MAP, TPS, and actual manifold temp because it was so bad with an unheated manifold. Works well during normal operating conditions. Still has some slight momentary hesitation or stumble at times, but only when I do something intentional, like stab the gas down to the floor in fourth gear at 30 MPH or something like that.

 

Thanks for the replies.

The noise you could hear was actually the injectors pulsing. They were actually buzzing. You could not hardly hear it under the hood, but somehow it was real annoying inside the cab. I took the spacer off and it went away.

When you say heated manifold, are you talking about the exhaust crossover? My performer still has that and I didn't block it off. I forgot to mention that I am running a 14" K&N open element.

I did some more testing yesterday. If I stab it from a dead stop full throttle o2 volts are about .800-.850. If I roll into it on a hill and go to full throttle, the voltage only goes up to about .650 to .700. When it stumbles, the volts are about .800.

Is there any thing I can do without burning a prom for this thing? I just don't have enough of a handle on it to jump in yet, and I don't have the time to learn it.
Am I running enough fuel pressure for my current combo?

Thanks
Lynn

 

Its hard to tell without a wideband, but the stumble could also be due to it being too rich on tip-in, or some other issue, like maybe the computer suddenly pulling alot of timing due to knock, but usually thatll just cause the engine to nose over and not stumble.

Youll at least need a cheap prom burner and prom adaptor. Ideally you should also have a wideband. Up front costs are more, but in the long run, it saves money. Tuning the steady state fueling used to be several hours of datalogging and some guesssing. With the wideband, it takes a mere 15 minutes. Itll probably takes longer with the stock ECM, but it'll eliminate alot of guesswork and speed things up.