Injector issue with 1990?

[cp1joel]

Hi all,

I own a RHD 1990 ZR1 here in Brisbane, Australia.

It has had some work done to it, reground camshafts, and new headers. Also I recently installed a calibration chip by Marc Hailbeck. Car has 20k Miles.

Before I installed the chip, the car was idling high, hesitation followed by a massive surge of acceleration. Also was difficult to start when the engine was warm.

Hats of to Marc, very impressed how much his chip sorted out the idle and acceleration problem.

Anyway to the problem. The car is great when cold, but after it warms up there seems to be an issue. After coming to stop - start highway traffic, the cars Idle was becoming erratic. More so when travelling very slowly, clutch in, out etc. Feels as though it is going to die and running rough but doesn't drop below 900 RPM. Once the traffic cleared, I noticed that it was lacking power. Once I got up to highway speeds the power seemed to come back and was back to normal.

Seems to be a bit of shaking in 3rd gear with WOT.

Also the car has a very noise flywheel, which was becoming very apparent when idling, moving slowly. According to Marc, he believes this is an injector issue which is causing an imbalance.

Would appreciate some help with this. Would be great to finally getting the car running great.

note - the injectors were replaced a couple of years ago.


Regards

Joel

[George Maz]

Quad-pack.
There are two, one may be bad.
Mine felt down on power, rough, like it was down a cylinder. Put it in fourth gear at 20mph, let it roll up to 40mph ...if it shudders, you're down a cylinder.

At idle, it sends a bad harmonic down the exhaust, which sounds like a chattering flywheel. I actually have a video of this. https://youtu.be/MHc84mj3zgQ

RH drive....cool.

[efnfast]

If the injectors were replaced with OEM, they still are not ethanol tollerant. Do you use guy use ethanol down under?

[Paul Workman]

If it hadn't been said already, I'd be looking at injectors.

If I'm not mistaken, Dynomite (Cliff) has one of my posts from like 8 or 9 years ago in his SOLUTIONS archive with a color graphic showing the pin-out for the injector relay connectors. From there you can measure the resistance of the injectors to determine which (if any) are bad.

And, to Steve's point, does your fuel contain alcohol? And, too, my injectors were replaced when I bought the car...with New Old Stock (NOS) injectors. Two years later I was having what sounds like the same idle issues your are PLUS some full throttle issues as well, also related to the bad injectors.

Get the motor up to operating temperature before measuring the resistance (to avoid a temporary "normal" reading), and then measure the resistance of each injector (coil).

And, by the way... What you're experiencing doesn't sound like anything too difficult to fix!

[cp1joel]

Quad-pack.
There are two, one may be bad.
Mine felt down on power, rough, like it was down a cylinder. Put it in fourth gear at 20mph, let it roll up to 40mph ...if it shudders, you're down a cylinder.

At idle, it sends a bad harmonic down the exhaust, which sounds like a chattering flywheel. I actually have a video of this. https://youtu.be/MHc84mj3zgQ

RH drive....cool.

George, would you mind confirming what you mean by Quad-Pack?
Interesting about being down a cylinder. If I was down a cylinder, would it be down continuously? Excuse my limited mechanical knowledge ( I am slowly learning ! )

And for the full power to come back once I regained highway speeds?

Also the video you sent me, the knocking sounds like it has a certain rhythm, where mine is more spontaneous, louder then softer. I will take a video when I can.

If the injectors were replaced with OEM, they still are not ethanol tollerant. Do you use guy use ethanol down under?

Steve - as far as I can tell from the previous owners receipts, the Injectors were supplied by Jerry's Gaskets in 2015. The type I am not sure about. I normally fill the car with 98 octane fuel which does not contain ethanol here. We do have ethanol fuels but are used in 91 RON.

Paul - Will look into finding this diagram and hopefully it is injectors.

This has only ever happened once before when I felt the car was lacking power. Normally the car will go like a bat out of hell! The car doesn't get driven much so may be contributing to the issue. Usually on starting ( cold starts are fine) the engine will shake, looks like it is hunting for idle. Not sure if this is normal?


Thanks for your help with this guys. Much appreciated.

Joel

[efnfast]

98 octane? DUDE!

[cp1joel]

98 octane? DUDE!

What is the issue with this?

This is also the fuel Marc calibrated the chip for.

Cheers

[DRM500RUBYZR-1]

What is the issue with this?

This is also the fuel Marc calibrated the chip for.

Cheers

98 Octane!


We are all just jealous!
Would love to pull up to a pump and get 98 octane!!!


We need to buy Race Gas to get that kind of octane, and it is not on every corner!


Very cool!
Marty

[BigJohn]

Yep we all need 13 to 1 compression!

[Paul Workman]

George, would you mind confirming what you mean by Quad-Pack?
Interesting about being down a cylinder. If I was down a cylinder, would it be down continuously? Excuse my limited mechanical knowledge ( I am slowly learning ! )

And for the full power to come back once I regained highway speeds?

Also the video you sent me, the knocking sounds like it has a certain rhythm, where mine is more spontaneous, louder then softer. I will take a video when I can.



Steve - as far as I can tell from the previous owners receipts, the Injectors were supplied by Jerry's Gaskets in 2015. The type I am not sure about. I normally fill the car with 98 octane fuel which does not contain ethanol here. We do have ethanol fuels but are used in 91 RON.

Paul - Will look into finding this diagram and hopefully it is injectors.

This has only ever happened once before when I felt the car was lacking power. Normally the car will go like a bat out of hell! The car doesn't get driven much so may be contributing to the issue. Usually on starting ( cold starts are fine) the engine will shake, looks like it is hunting for idle. Not sure if this is normal?


Thanks for your help with this guys. Much appreciated.

Joel

Being that Jerry supplied the injectors in 2015, I'm sure you have the alcohol-tollerant version. But, if you have NO alcohol in the fuel anyway, then it is a moot point. Prolly something else, e.g., fuel pumps/pressure - that sort of thing, maybe.

[jss06c6]

Man, it's been a long time since we've seen 98 or 100 octane fuel! Brings back fond memories of big block solid lifter engines at 13:1 compression and a BIG cam!!
I
Have you checked your fuel pressure? It does sound like a fuel issue...

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[cp1joel]

That is interesting ! I would have assumed the US would be getting higher octane fuel as well. Quite a few years ago 100 octane was available in some locations, but now 98, 95 and 91 are readily available.

I have not checked the fuel pressure, good point indeed.

I did notice when the issue was happening, the oil pressure gauge was dropping to about half way when coming to idle, then moving close to or above the 3/4 mark on the gauge.

I don't recall seeing it fluctuate like this before ( I may be wrong).

I am taking the ZR1 to a mechanic on Friday, getting him to give it a good look over and try and sort some of these issues out. He is well recommend for woking on chevy and high performance engines. Very difficult to find anyone who will touch the LT5 in Aus given the low numbers here.

Will keep you all posted on how it all goes.

[BigJohn]

We have 93 here!
E-85 is 105.

[gtcollins@maxnet.co.nz]

Hi All our fuel here in the South Pacific is rated with the ron (Research Octane Number ) where yours is mon
(Motor Octane Number)
So our 98 is about your 91 or 93 when I got my ZR-1 po said he ran it on our 91 I tyred it and the engine detonated so I only run BP 98
Regards Glen Collins

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[WARP TEN]

Now I realize I am dating myself, but in the early 70s I used to fill up my '68 Hemi Road Runner with Sunoco 260, which was 104 octane. It needed it to run well. Wish they still sold that. --Bob

[BigJohn]

Local Sunoco has Cam2 racing fuel.

[Rodder]

In Europe the octane is rated in RON aswell and US use RON+MON/2 which gives a lower value. In Sweden we have 95,98 and E85. An old car magazine test showed our 98 to equal a US rating 92,5 to 93,25 depending on brand. Today some 98 octan is ethanol free depending on refinery the rest is "said" to be up to 5%.

Thomas

[gtcollins@maxnet.co.nz]

Our BP 98 is ethanol is free Mobil isn't
Glen

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[George Maz]

"Quad-pack"
This module controls injector function on 1990 Z.

[5ABI VT]

Me personally I have been mulling over the fuel pressure regulator of late. Few have changed it, some have posted pics and they didnt look too good inside. I wonder as all of our cars are similar in age if it would be a good idea to replace it. Any records of fuel pumps being replaced?

[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.

[cp1joel]

hmm after speaking to the original mechanic this morning, he believes the cams were too big for the car. The car was intended to be for racing rather than street. He made a suggestion to put the original cams back on and original chip. According to him the car ran beautifully and was much more pleasant to drive in its stock form. What are your thoughts on this? If it was up to me I would have kept the car stock to begin with.

[jss06c6]

Trying to troubleshoot without being there or getting codes to assist with guidance is not very fruitful. As a personal comment, I find it very hard to believe that Marc could not hit a 95% tune on your car IF he knew exactly what had been modified AND that you have no other issues, either mechanically or electronically with the car. If you told him what the cam specs were, I'm confident he could hit the tune, or told you the cam specs were incorrect for the LT-5. More likely, you have something else going on, or the cams were not installed properly to begin with (inaccurate timing).. My $.02..

[BlackSheepz]

Just read through the thread.
I'd personally stand by Marc Haibeck's chip but that's just me. He's a magical space ninja, I don't think there is anyone that knows more about these engines than him.

I Was also having problems with my car a few weeks ago. Car ran well, but also had a hesitation on hard acceleration. I'd floor it and it would accelerate adn then at about 4000RPMs it would feel like I floored it again! Big burst of acceleration. I always thought I had a vacuum leak, but then I started getting the shudder and sound like you describe.
Marc Suggested it was the injectors and that the flywheel was compensation (as you have suggested foryour car).

I replaced my injectors (First and only plenum pull and it was solo, yikes!). Car started and ran beautifully after that but the hesitation was still there. Marc suggested the 02 Sensors. Got hte new O2 sensors from Jerry and replaced them when I put a Corsa Exhaust on the car last week actually. When I first started and ran the car it was AMAZING. Then when the car warmed up I floored it to accelerate and holy sh*t things were NOT ok. The thing shuttered, started to go, bogged down, started, bogged and that was it. Car went into check engine light territory and just did not run well.

Next step was to replace the fuel pumps. This was the solution for my car. When I pulled the pumps one of the hoses was very badly cracked and the fuel strainers crumbled in my hands. I replaced both pumps, and the hoses and now the car runs better than It's ever run in my ownership.

To make a long story even longer, have you checked your Fuel pumps?

If Marc made you a chip, and he didn't freak out when you told him the specs of your cams and mods, then I'm guessing it's not the ECM or the cams that are the problem.

[cp1joel]

Hey all,

I totally stand by Marc's chip as well and believe he tuned the car as to what I supplied him.

Correct me if I am wrong, but the tuning on his chip eliminates any tuning done to the original calibration package (blue cover)? So this means that the car would be only reading his tune right?

Spoke to the mechanic this morning, has he said the car dyno'd about 380hp at the wheels. That is roughly 100 less than the dyno done a couple of years ago.

He still think the tune is totally wrong and that is what is causing the car to be super lean under 3000 and super rich above 3000. He doesn't believe it is anything else (that I have suggested).

As you can imagine I am stuck between two places, but I will bring the car home and investigate further.

So it will be injectors, spark plugs, coils, MAP sensor hose and fuel pumps as possible culprits.

Cheers guys

[jss06c6]

What is your tuner using to measure fuel trim in the VE tables? What BLM numbers is he seeing? Has he looked at the PE table to see what it's commanding? There are two VE tables and two spark advance tables, one set for "port throttle closed" and one set for "port throttle open" (secondaries closed and open). I'd be interested in knowing what your tuner is seeing as "super lean" and "super rich".

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[Ccmano]

Is this the same guy that said the cams were too big? If so I think it's time for a new mechanic/tuner. The problem I see quite a bit these days is that today's technicians don't understand or can't fully read these old obd1 memcal systems. I'd be curious to know what software he is using.

I suggest you get yourself the proper software (TunercatRT which is free) and cable to connect to the Odb1 port under the dash.

http://www.moates.net/aldu1-and-cabl1-p-127.html?cPath=64

Load the software on a laptop and do some datalogging. Datalogging is simply driving the car and letting the software record what the system is doing. 10 minutes of driving with a few full throttle runs is all that is needed. The data file can then be sent to Marc for analysis.

This will help Marc understand if there is a mechanical/sensor issue or if the tune is correct.

Good luck
Hans

[jss06c6]

Is this the same guy that said the cams were too big? If so I think it's time for a new mechanic/tuner. The problem I see quite a bit these days is that today's technicians don't understand or can't fully read these old obd1 memcal systems. I'd be curious to know what software he is using.

I suggest you get yourself the proper software (TunercatRT which is free) and cable to connect to the Odb1 port under the dash.

http://www.moates.net/aldu1-and-cabl1-p-127.html?cPath=64

Load the software on a laptop and do some datalogging. Datalogging is simply driving the car and letting the software record what the system is doing. 10 minutes of driving with a few full throttle runs is all that is needed. The data file can then be sent to Marc for analysis.

This will help Marc understand if there is a mechanical/sensor issue or if the tune is correct.

Good luck
Hans
Exactly!!

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[cp1joel]

Hi all,

thanks for the suggestions so far, will look into data logging.

A bit of an update on the ZR1.

Received the car back from the mechanic, they looked over the entire thing.

Checked injectors, spark plugs, fuel pressure, compression, o2 sensors etc and are still adamant that the issue likes with the tune.

What is interesting is that Marc tuned the car for stage 1 cams.

I have been told by a couple of people that the cams were reground at a much more radical profile. I wonder if this could be causing the issues I am having? I may have provided him the wrong details.

I have print outs with the cam spec and believe they are up to date but I have a feeling they are not Stage 1.

Is anybody able to look at these print outs?

Thank you all
https://i.imgur.com/MuYJL5P.jpg

https://i.imgur.com/Id8VPBD.jpg

[5ABI VT]

Hi all,

thanks for the suggestions so far, will look into data logging.

A bit of an update on the ZR1.

Received the car back from the mechanic, they looked over the entire thing.

Checked injectors, spark plugs, fuel pressure, compression, o2 sensors etc and are still adamant that the issue likes with the tune.

What is interesting is that Marc tuned the car for stage 1 cams.

I have been told by a couple of people that the cams were reground at a much more radical profile. I wonder if this could be causing the issues I am having? I may have provided him the wrong details.

I have print outs with the cam spec and believe they are up to date but I have a feeling they are not Stage 1.

Is anybody able to look at these print outs?

Thank you all
https://i.imgur.com/MuYJL5P.jpg

https://i.imgur.com/Id8VPBD.jpg



I would imagine you did send the specs to Marc to see what he thinks ? He usually replies very fast.

[cp1joel]

Yer this is what I sent him for the tune.

He mentioned that they were US Stage 1 cams.

So maybe the tune is correct after all?

They were purchased as Stage 1 cams and reground here in Australia.

[XfireZ51]

If I am reading this right, ur cams are 238 intake/232 exhaust? Is this a 5.7L?
Pete could probably chime in, but bigger exhaust cams are not needed for a stock block LT5. And IMO, every motor is different and particularly one with non-stock cams will require custom tuning. I'm not suggesting that is the issue w ur ZR. Before tuning anything, u need to make certain that fuel, air, spark systems are all operating correctly.
Are ur secondary throttles removed or disabled?
Here's Pete's suggestion

http://www.zr1.net/forum/showthread.php?t=26684&highlight=Pete+cams

[jss06c6]

A lot of very qualified people have spent time trying to diagnose the issue(s). Without actual data, we're driving with one hand on the wheel and one eye closed. Each engine has a finger print. No two are alike and each require, for optimal performance and efficiency, an exact combination of fuel, air and spark. Making a change in your cams has a dramatic impact upon the volumetric efficiency of your particular engine. If you want to know how your setup is performing, I strongly suggest you get proper hardware and software to log engine data. Once you have this, you can post up a .CSV file so that Marc and others can properly diagnose what is really going on.

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[Top Toy]

Your cams are relatively mild with the exception of exhaust duration. Lifts are a little less than most at 0.42" intake and 0.41" exhaust. Intake duration at 238 deg. is in line with most but exhaust duration at 232 deg. is longer than most and would make tuning for low speed more challenging. Could be a contributor to your problems. Probably not optimum for peak torque/power either. If you still have operating secondaries, suggest you eliminate them. Makes tuning a whole lot easier if you don't have to worry about when those open up. Marc would need to know whether or not your secondaries are in service to give you a proper tune.

[cp1joel]

Hi all,

Once again thank your for all your input and advice.

I have been back and forth with Marc in regards to the cam size and tune.

His next recommendation as with a couple of you guys, is to log the data when driving and send the file to him. Have ordered the OBD1 connector and will do this as soon as it arrives.

He agrees that bigger cam's should not be added to a 350 engine, and this is contributing to my rough idle/lean issues.

He will try and smooth out the fuel and spark and we will see how we go from there.

He also agrees that if I am still not happy, I will return to the original cams. Should be making only 20hp less and smooth out the idle and drivability.

Thanks for all your help again and will keep you all posted

Joel

[XfireZ51]

Joel,

Let me suggest that u just replace the exhaust cams w the stock ones. It makes for a great combo. Very nice w good idle quality and smooth power. Had that setup for a few years and really liked it. Would recommend that to you.

[cp1joel]

Hey all,

So as I await for my obd1 reader, I decided to to start the car this morning. Put the key in the ignition and was surprised to hear that radiator fan come on continuously. The car starts but will die as soon as I stop giving it some gas. Runs terribly at around 500 RPM, stumbles and dies. Very odd as the other day it was fine and has never done this before. Took Marcs chip out and it still did the same thing. Disconnected the battery and no luck. Noticed service enginr soon light is on. I thought even if the fan was on continuously this would have no effect on how the engine runs. Trying to figure out where to start with this.

[XfireZ51]

Hey all,

So as I await for my obd1 reader, I decided to to start the car this morning. Put the key in the ignition and was surprised to hear that radiator fan come on continuously. The car starts but will die as soon as I stop giving it some gas. Runs terribly at around 500 RPM, stumbles and dies. Very odd as the other day it was fine and has never done this before. Took Marcs chip out and it still did the same thing. Disconnected the battery and no luck. Noticed service enginr soon light is on. I thought even if the fan was on continuously this would have no effect on how the engine runs. Trying to figure out where to start with this.

Have u tried re-seating Marc's chip? When u turn ignition to ON, but do not start motor, does SES light flash once? It should if all is well w ECM.
Fans turning on with key ON is a sign of a problem w the calibration/prom. Its "limp home" mode.

[Ccmano]

Check the vacuum hoses on the MAP sensors.
H

[Hib Halverson]

Admittedly, I'm coming onto this thread late in the process. Nevertheless, I'd like to offer some opinions.

1) One post said the car made 380 at the wheels. That is about 464 at the flywheel–which is not bad for a 2-bolt motor which has cams, no headwork and headers. If this car is running as bad as suggested in posts by the OP, those dyno numbers are a bit suspect. The OP stated the "mechanic" said the engine was lean then rich in PE (secondaries enabled). Does this guy have any information more specific than just saying it's "lean" or "rich". If so, post the air-fuel ratio data he recorded during the dyno session. Actually, ask him for all the data from the dyno session and post it here.

2) The very first post states clearly that the engine runs ok after cold start and during early warm-up but once the ECT comes up, the idle stability goes away. Without seeing some serial data, I'm guessing, but I'll bet this engine's fuel trims are whacked when it's at idle/part-throttle in closed loop. It's possible that's because of the cal but, considering the cams are said by others here to not be too radical and it's got one of Haibeck's chips, at this point, I don't think that's probable because, as long as the engine specs, as communitated to Marc, were correct, his cals are usually pretty close.

3) The OP talks about the service engine light coming on. Why hasn't the mechanic involved connected a scan tester to the engine and read any current or history codes in the ECM?

4) I'd be looking at various engine controls components, like oxygen sensors, MAP sensor, vacuum hoses etc.

5) (snip)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.

"DRM500RUBYZR-1 gets the weekend "Beacon of Reality Award". Please consider his suggestions

6) Run the fuel pressure tests in the Factory Service Manual and post the results.

[cp1joel]

Hi all,

I checked the module and it seems to be connected fine. I took Marcs out and it did not make a difference.
SES remains on (does not flash), with radiator fan going.

Used a paperclip to to connect A to B but to no avail.
A to G worked fine and it threw 1- C41, H41, H74. Also 4 - Err

Am I correct to say that there is no communication with the ECM?

It just seems very odd that this could happen all of a sudden.

Thanks

Joel

[cp1joel]

Hmm after doing quite a bit of research I came across a thread with the exact same issue and same symptoms.

SES light stays on, fan on.
Throwing the same code (c41)

turns out to be the optispark /distributor.

Will begin to look in this direction

http://www.corvetteactioncenter.com/forums/c4-general-discussion/135631-module-1-c41-module-4-err-module-9-h72-6.html

[QB93Z]

The LT5 in a ZR-1 does not have an Optispark.


Jim

[cp1joel]

Oh right, I assumed the LT5 used a similar distributor to the LT1.
If that is the case, I am still leaning towards a bad ECM.

[DRM500RUBYZR-1]

ECM's, while known to fail, particularly if they get an electrical surge from a high powered charger, usually are rather robust in a C-4.


I would suggest searching for a faulty wire first.


You and others have been doing a lot to that car recently, so it is not impossible that the ECM took a dump, but I would rule out the higher probability causes, such as loose connectors, shorted wire etc.


You will likely have time to perform those checks as an ECM may take some time to locate.


Let the FSM be your friend and follow it's diagnostic protocols.


Good luck and keep us posted.


Marty