I took my 88 IROCZ (5.7) to my mechanic to have some performance parts installed. He installed a set of Flowtech headers (w/o air tubes, w/o oxygen sensor), a Flowmaster cat back exhaust system, gutted converter, Dart aluminum heads, Compcam roller rockers, hardened push rods, Edelbrock aluminum TPI manifold base (for aftermarket heads), Edelbrock aluminum air runners, and Edelbrock valve covers. We plan to add a larger throttle body and mass air flow sensor in the spring. He removed the air pump and air tubes. The car also has K&N filters and an older (1989) Hypertech (off road) chip. To my knowledge the engine ran properly when I took it in (no check engine lights and idled and ran smooth). After all parts were installed and motor running he tells me that the motor is getting too much gas. I’m not sure how he knows this. He assumed there was a problem with one or more of the injectors (all 20 years old). He removed them, sent them in to be tested and found one that leaked. That injector was replaced and the motor was re-assembled. Same problem…..motor getting too much gas. He blocked off the cold start solenoid to make sure that was not the problem. Motor still getting too much gas. He tested the fuel pressure and found that the system holds pressure until the motor is running, then loses pressure when the system dumps too much gas into the motor. Took the fuel induction system apart again and found that the system holds pressure until the fuel rails (stock) are bolted to the intake manifold. For some reason the system looses pressure when the fuel rails are bolted to the manifold and then dumps too much gas into the motor. Fuel intake system is now apart again and he is going to use a scope to see which injector(s) are dumping too much gas into the system. He tells me that he has made these same changes to many L98 engines over the years and that he has never encountered this problem before.

Does anyone have any ideas what is happening here? Also, how much do repair shops usually mark up their prices on parts?

I should also add that when starting the engine (cold) the temp gague shakes and jumps up to 265 and most of the time stays there. I have taken the face plate off and tapped the needle with my finger. It falls back to zero and then works properly. This was happening before I took the car in for the performance parts. The mechanic is aware of this.

Thanks,

Brian

Update: Scope test revealed one injector that appeared to be stuck open and two more that leak. Decided to order all new ACCEL performance injectors. Probably should have done this at the beginning of the project. We are not to the point yet were the engine runs too rich.

 

Instead of modifying my L98 I took it out and replaced it with a crate Votec TPI motor from Scoggin Dickey last month. It sounds very similar to your setup.

In addition I have a 52mm TB, desreened MAF, 24# inj. and SLP runners that help with fuel/air delivery. My car is running too rich also, even with a custom tuned chip from PCMFORLESS.

I called them and I'm going down there to Dyno/Tune the car. It seems to be the only way to lean the car out correctly.

It sounds like the mechanic is trying to mask the problem. I'd try to find a tuner for OBD1 computers in your area.

 

How does your Flowmaster exhaust system sound?

 

What did you do about the oxygen sensors??

 

There's your problem.

 

yeah i would say that once you get the new injectors you should have it dyno tuned w/ a wideband o2 sensor. That way you will be able to know that you are getting the correct a/f mixture all the way through the rpms, that is more or less the only way you can be certain.

most shops charge at least 15-20% markup on the parts they sell.

 

It was running rich before I desreened. My chip was programmed for a desreened MAF and I had not done it yet so I thought it might help. I cant tell if it leaned out but I'm getting a Dyno/tune soon

 

You said your headers were w/o o2 sensor provision?? if it only starts going super rich after it warms up a little there's your problem. The computer needs the o2 sensor signal to adjust fuel injector pulse width. Obviously, leaking/stuck open injectors will be a problem too, but the computer needs that sensor to operate the injectors properly. (BTW, it will be seeing 0v from the sensor, if there is no sensor, which it interperates as super lean, and dumps in fuel to raise the voltage)

wouldn't getting the injectors flowed/cleaned made those 3 other faulty ones apparent? Do a search on Accel injectors, I think you will find a lot of people do not have very good reliability with them. They seem to crap out after a few months, just an FYI.

have your mechanic test to see what kind of signal the injectors are getting, possibly if there is a short, it is having the effect of telling all of them to stay open. remember these car are batch fire, meaning all of them fire at once, not one at a time like new cars, so if it is a command problem, it's likely to affect all cylinders.

Let us know what happens.

 

I heard the same thing about Accel injectors.

So far I've heard all good things about SVO Ford injectors.

http://store.summitracing.com/partde...5&autoview=sku

 

Your mechanic said hes done similar things on an L98 before but yet he takes out the O2 sensor and expects nothing to happen? Your mechanic is a MORON...no offense if hes your friend or in your family but thats stupid as hell.

You NEED that sensor,w/o it your computer has no idea how much fuel to put into the motor and thats why its running waaay rich. Now the stuck open and leaky injectors are some of the problem...but your gonna spend $350+ dollars on them and its not going to completely fix the problem.

 

My mistake.....the headers do have oxygen sensor port. I don't know if new injectors have been installed yet. I'll update when I hear.

 

Well, good to hear that it has the o2 port, I'd be very worried otherwise. I hope the new injectors do the trick.

 

The new injectors have been installed and the car is finished. Motor runs good and pulls hard. Flowmaster cat back system sounds incredible! Thanks for all your input. This spring I will be looking at larger throttle bodies and mass air flow sensors. Any suggestions?