Injector issue with 1990?

[cp1joel]

Hi all,

Bit of an update to the situation with the car.

The mechanic has had a good look over it and thinks the problems are coming from the computer and wants to replace the computer and properly tune the car himself. This is not cheap and will cost about 4k.

He says the injectors are fine and has also spoken to the mechanic who previously worked on the car. Apparently the car has always run terrible under 2500 RPM and the issue with the knocking started after a tune quite a few years ago.

What are you thoughts on this ?

[jss06c6]

Certainly don't understand the need to replace the ECM (computer). I can understand the need to retune, but that does not require replacing the ECM. He should be able to put a new EPROM in the computer with a new tune. Have a look at the Moate's website and TunerproRT website for some guidance.

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[jss06c6]

Should not be anywhere near the price he is quoting..

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[cp1joel]

My correction, as you said jss06c6, he will not replace the ECM, just put a new chip in the car.

I called the previous place who tuned the car a couple of years ago and they only ever gave the car a run in tune. This was due to time restraints. They said there was approximately 3k worth of tuning to do on the car.

Apparently it is very difficult to tune a car with 16 injectors with the longer duration camshafts.

[jss06c6]

You might consider simply calling Marc Haibeck to let him know your setup and buy a chip from him.. I would not cough up $3,000 in tuning time.

Yes, when running secondaries, there are two sets of fuel and timing tables to work with. Not that difficult if you know what you're doing. Your tuner needs to be able to work in an OBDI environment versus modern OBDII computer systems.

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[cp1joel]

The thing is I already have a chip installed from Marc. He programmed the chip exactly for my car (camshafts, headers).

I think the issue the mechanic is having is with the tune done on the original calibration package on the ECM. He will install something that does not effect Marc's chip rather gives him the ability to tune the car.

Marc replied today and insisted that his tune was correct and to look for a misfire or a problem with an oxygen sensor (Oxygen sesors were replaced a couple of years ago).

The mechanic after putting the car on the dyno feels that the issue lies with the tune (and so did the precious mechanic who worked on the car for 15 years). The car is very lean and then super rich when the secondaries are open.

Thanks for your help

[DRM500RUBYZR-1]

Your first post states that you installed a chip from Marc.
Was he aware of all of the mods and each of the problems that you were experiencing?
Something is not adding up here.
With utmost respect to your current mechanic, I would suggest holding off a bit and going back to check out all of the basics before trying to fix a basic performance problem with an advanced dyno-tune.
Everything that you indicate as a problem, all seem to be simple misfire issues. Fuel or ignition are usually the culprit absent a mechanical problem, which is less probable, as you say it only happens at low RPM.
Look first for simple causes, perhaps multiple simple causes before investing thousands elsewhere.
While we would think the injectors to be fine, could there have been an issue during the install?
Pinched wire?
How are the coil packs.
Let's start at step one and move forward.
Lots of helpers subscribed to this thread already!
It will be figured out!
Marty

[cp1joel]

Thanks Marty !

I guess after wanting the car to be running well for so long, I feel like letting the mechanic just do his thing.

But your right, lets go back to the start.

When I purchased the car, it had sat for over a year ( well most of its life ).
The previous owner had spent thousands on longer duration camshafts, new headers, exhaust etc. As I said the car was given a run in tune after this was done. The tune was never finished.

Ever since the first time I drove it the car has always had that flywheel knock when warm, hard to start when warm and seemed to have high idle. Always smelt rich too. The car would also idle high when stopped and then drop back to normal. A couple of times starting the car when warm, it would misfire, splutter and die (quite a surprise). I have learnt to hold the key on for longer to prevent this from happening. Another issue was hesitant acceleration. The previous mechanic suspected the throttle body was becoming stuck open. Marc's chip seemed to fix this.

I decided to order a chip from Marc. He viewed all camshaft documentation and all the modifications done to the car. He programmed the chip and I recently installed it. First thing I noticed was the idle had dropped to about 900 and seemed to be more comfortable. The car would still seem to hunt for idle and the engine shakes. Could not balance a nickel on it that is for sure.
This also seemed to fix the high idle when stopping problem as well.

The car really got to me when as I said, I was stopping and starting on a highway. The car felt like it was going to die, and lacked power until I got up to speed. After this it was fine again. However, when changing down to 4th gear and WOT the car would hesitate and stutter.

I suspected the injectors as well.

The old mechanic noted that the car made the knocking sound only after the last tune was carried out. Also pardon the question, the blue calibration package on the ECM is an original component of the LT5? Or is that an aftermarket part which is added by a tuner?

Thanks for all your help again guys. Much appreciated

[A26B]

Just read through the complete thread. I suggest we switch from road speed to engine speed/rpm for the sake of discussion. Here's why; Marc's calibration (Prom/chip) retains the factory open & closed loop feature. Once the engine reaches operating temp, both open & closed loop is enabled.

The first step I recommend is to pull the stored DTC's (Diagnostic Trouble Code) & write them down. Then, disconnect the + battery cable for a couple of minutes & reconnect. Start & operate until the engine has exceeded 180f temp. You may or may not see a console light for SES (Service Engine Soon), depending whether the bulb is working or still present. Shut it down & pull the stored DTC's again.

Stop here & post the codes here on the forum.

I agree with Marc regarding the O2 sensors. A shorted sensor electrical connection (water in the connector or burnt wire from header contact) will cause the engine to run very bad in closed loop (under 3,000rpm) & much better in open loop (above 3000rpm), very similar to the conditions you describe. But let's not get ahead of things & look at the DTC's first.

Footnote: I have experienced a shorted O2 sensor & the engine runs very poorly until open loop rpm is achieved.

[cp1joel]

Hi Jerry,

Thanks for the information. I will look into pulling the stored DTC's as you suggested.

Another note that I forgot to mention was ever since I first drove the car the SES soon light would come on sometimes after WOT, and would then disappear.

Since I installed Marc's chip I have not seen the light come on, only the ABS light momentarily.

I think for now, I will just bring the car home. I can't justify the amount I have to pay if it might not be the solution. Also the great advice I have had from everyone here regarding the situation.