Ignition module ground

[8upZR1]

I was looking at the schematic for the LT5 ignition module and saw that it has external and internal grounds. I realized then that the internal ground on my module has not been connected as I have removed the module from under the manifold for troubleshooting and now lay it on the windshield. I have since added an extra ground wire to the heat sink plate to simulate the internal ground, but it has had no positive effect. I was wondering if it is possible to fry the ignition module by cranking the motor without this ground attached. Anybody have a clue?

[Tyler Townsley]

Shipped the dis checker and scope today. Should help answer that question.

Tyler

[8upZR1]

Thankyou Tyler, I will forever be indebted to you. If you are ever in the Thunderbolt/Savannah area and in need of food/shelter/clothing please do not hesitate to ask.

[Tyler Townsley]

There is a pigtail so you can check the module without removing the it. In your case you probably need to pull the module and look at the signal as it comes out of the module before going to the coil. On one of my dis modules the signal looked good until it got to 400 rpm then it became obvious it was bad as the signal lost its uniformity. I just hope it helps.

Tyler

[8upZR1]

I hope so too. At this point I am totally stumped. Ever since this problem started I have removed the module from under the plenum and now I just lay it on the windshield so that I can switch between modules and troubleshoot without hassle. Once the car runs I will find a suitable location and lengthen the harness so that I do not have to mess with the plenum to access the DIS. I cant imagine that both of my modules are broken but if they are I will actually be pleased to know what is causing my problem. At this point I am worried that the modules will check out OK. What then will I do? I have learned from the previous owner that the car has gone through four ECM's. In addition I used to have a problem where the car seemed to run extremely rough and lacked power, but this situation only occured when the motor was cold. Once the engine got to the upper range of the temp gauge it would run great. After I installed a chip the motor never got hot enough that the problem went away so I had to ditch the chip. Nobody I have asked has ever heard of such a problem. Most of the time things get worse as the car heats up, not the other way around. I am thinking maybe this vette is cursed and I will never get everything sorted out properly.

[Tyler Townsley]

4 ECMs? There is wireing problem between the ecm and the dis module. I think you will find the DIS module is bad. You need to use the schematics here and chase out every wire to the end. IE pull the connectors at the ecm and dis and run a continuity test end to end. It almost sound like your ecm in and tach out lines are switched on the dis. This is the major difference between the 88/89 cars and the 90+ cars is that wireing difference. If someone was using a 89 refrence for the wiring or replaced the engine compartment harness with a 89 that would be the problem. After chasing the wireing use the other refrences to make sure you have the right info on the line.

http://www.sirgalahad.org/tyler/misc/90ecm1.jpg
http://www.sirgalahad.org/tyler/misc/90ecm2.jpg
http://www.sirgalahad.org/tyler/misc/90ecm157.jpg
http://www.sirgalahad.org/tyler/misc/90ecm158.jpg
http://www.sirgalahad.org/tyler/misc/90ecm159.jpg
http://www.sirgalahad.org/tyler/misc/90ecm160.jpg
http://www.sirgalahad.org/tyler/misc/90ecm161.jpg

Guess I should have included the ecm breakout box too.

Tyler

[8upZR1]

Continuity between the ECU and DIS wires was one of the first things that I checked, and everything checked out OK. I dont have an oscilloscope but I did hook up a volt meter to the DIS ref out high, ref low, est signal input, tach output, and bypass circuit, at the diagnostoc connector and they all looked good, at least as much as I could tell. The voltmeter averages the high and low and what I got was 2.5V ref high, 0v ref low, .3V est, 3.6v tach, and 0v bypass. This is exactly what the manual says I should get. Obviously the osciloscope is the only way to know exactly if the square wave is being produced but this seems bad to me. My only concern was that maybe the est signal was a bit high, but I guess it is close. The timing should be non existant if some critical wire is unplugged, but I am still getting combustion from all intake ports. I hope to die having solved this issue......

[Tyler Townsley]

4 ECMs is not a good thing. You will be able to look at the waveforms with the scope I sent. Bad gas will sometimes cause symtoms you describe.

Tyler

[8upZR1]

Tyler, I have done checked everything I can and it all looks great. One thing I was wondering is what about the ISS is what RPM is it simulating when it is turned all the way down on the crank setting. I am getting that it is making 1800 RPM. At least that is what my MSD says and it is usually very accurate. Could this be my problem? I can't imagine that the cranking setting would be outputting 1800 rpm. When I turn the knob to the cruise setting it is making a signal equivalent to 6500 rpm. Kinda high for cruising but if this is normall then cool. I guess I will empty the gas tank and refill with new gas, but I doubt that it would make a difference. I was wondering how you have an 88 ZR1. Isn't 90 the first year? Is your 88 a transplant or an engineering mule or something like that?

[tccrab]

Originally Posted by 8upZR1

I was wondering how you have an 88 ZR1. Isn't 90 the first year? Is your 88 a transplant or an engineering mule or something like that?

Tyler's '88 ZR1 (Queenie) is the only surviving '88 prototype, and one of a handfull of prototype/test cars/mules that somehow survived even though GM had (and still has) a strict policy of destroying any and all development cars.
Here's a link to some nice pics of Queenie, and I've seen a nice writeup on her somehwere, ahha yes, here it is:
http://www.sirgalahad.org/tyler/prot...typesStory.doc
http://forums.corvetteforum.com/show....php?t=1172641

The earliest prototype I've heard about/seen is a 1986 ZR1, one of the 4 found in a Lotus boneyard in the UK. Here's a nice web site detailing the discovery and rebuilding of one of the cars found there:
http://www.eurovettes.com/zr1_story.htm
And a picture of the aforementioned Lotus boneyard:
http://corvetteactioncenter.com/gall...oto/775/sort/1

There's a 1987 prototype car in the NCM, here's a pic:
http://www.corvetteactioncenter.com/...sort/1/cat/all

There were a total of 84 1989 ZR1 evaluation cars that were built to promote the 1990 ZR1. Members of the press and special guests were invited to drive them and review them for their publications. Many of these cars most likely still survive, and show up at a few car shows every year. These cars are readily identified by their "salad shooter" wheels with the solid center caps:
http://temp.corvetteforum.net/c4/scoob/stealth02.jpg
'90 with exposed lug nuts:
http://www.96lt4.com/ZR1/myll90.jpg

TomC
'90ZR1 #792