Ignition module ground

[Tyler Townsley]

Originally Posted by 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?

The ISS crank setting is 400 rpm. I am unfamiliar with the MSD setup you are talking about. If the the spark event is reported as 1800 rpm at start then that is what the ecm and dis thinks the engine speed is. I would think would lead to a spark event in the cyl too far in advance of valve closing and cause backfire and an inability to start. If the gas is bad it will smell different. Using the scope compare the crank sensor and cam sensor signals to that created by the simulater, they should be the same.
Where is the rpm signal taken from with the MSD? On the zr1 the dis has a pin out that goes directly to the dash tach which is why the tach reports the rpm correctly and the aldl software does not read correctly over 6350.

The story of the 88:

http://www.sirgalahad.org/tyler/prot...typesStory.doc

Tyler

[8upZR1]

The MSD calculates RPM from the coil signal then outputs it in standard squarewave to drive a tach or shift light, or in my case a digital window switch for my NOS, it displays RPM. I will compare the two signals tomorrow. When a spark plug is laid against the intake manifold and the engine is cranked it is obviously a much slower spark sequence than when the ISS is used. I could tell immediately even without a scope. The sparks come much more rapidly from the ISS. Ifthis is in fact my problem then what do you think the cause is? Do you think it is the sensors failing to read properly or the DIS failing to read the signal?

[Tyler Townsley]

Originally Posted by tccrab

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://forums.corvetteforum.com/show....php?t=1172641

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

TomC
'90ZR1 #792

Same car. It was produced on the 87 assembly line in June of 87 with an 88 vin on the frame as a 88 production prototype.

Tyler

[8upZR1]

You are lucky to have come across such an amazing piece. Has the motor and tranny been put in? I would love to know how the car compares to the production ZR1.

[8upZR1]

The manual for the ISS says that U2 is the proper setting, do you by any chance remember if this is correct?

[Tyler Townsley]

Originally Posted by 8upZR1

The manual for the ISS says that U2 is the proper setting, do you by any chance remember if this is correct?

According to this:
http://www.sirgalahad.org/tyler/misc/dis_1.jpg
U2 is the correct setting.

It almost sounds like you have reversed the cam and crank sensor input on the ISS, ie 1800/4= 450 rpm the dis is seeing a cam signal and using that to calculate spark. The thing to remember is under 400 rpm the dis controls the spark based on the rpm input from the crank sensor.

Couple of questions, the dash rpm does not work? Is it bad or is the dis not showing a rpm signal on DIS pin E?

You said the car ran ok before the blown gasket yet you then qualify that by saying it ran ok once it got warm. Something to check is the wireing to the fuel pumps, in the zr1 on key on you get a 2 sec pulse in primary pump and when it is cranked bot pumps come on until ~180 degress when the secondary pump shuts off. If you have a way of checking the fuel pressure at the rail it should go to ~45 psi and hold there.

It is very difficult to diagnose from long distance and equally hard to diagnose alone using tips from online. Been there twice, once it ws a broken exhaust valve spring that took me 2 1/2 months to diagnose. Then it was the prototype which took 2 years to figure out.

The ptype is running but it took so much to get running that I may hae damaged the bearing as it has very low oil pressure, something I will fix in the future.

Tyler

[8upZR1]

OK I will clarfiy. The car ran 100% when the power key was out, absolutely not a single problem. With the key turned to full engine power and at full throttle the car would run like sh*t, unless it was hot. I know this car since it was new, it was purchased by a doctor in 1990 and sat in a garage untouched till about 96 (factory plastic on seats, 0 miles). One day the good docs mercedes had a flat so he tried to drive the vette. Obviously it didn't work, no battery, etc. I was banging his daughter at the time and he asked me to get it runnng cause he wanted to start driving it. I put new battery in and it ran great, awsome power, ZR1 power. He drove and abused the car like no other and things started to break, like the ECU's. The car sat outside for long periods of time and the paint went south. This guy drove the car 10 miles a day and literally never once put the valet key into the slot. Last year he tried to trade the car in for a Toyota and the dealership would not even give him 4K for the trade in value, so that is how I got it. It was totally screwed up when I took over and ever since then I have been fixing stuff. The full throttle/hot condition is only when the full engine power is on. I thought it was from the actuators so I pinned them open to see if that helped, it did a little but the car still did not perform like it used to. The doctor is super cheap and around here there is a gas station that gives 7 cents off premium on Tuesdays so that is what he filled it with, but the place puts something like 10% ethanol in the gas. This messed up the secondary injectors and I replaced those and it helped a little. All this time the car was running great except for the full throtttle/full power, low temp situations. When I pulled the heads I found that the secondary ports were comletely clogged with carbon and there was all sorts of large chunky carbon deposits in the breather areas of the valve covers. So now I am thinking that this previous issue was due to diminished cross sectional area of the secondary ports and hopefully it will be gone when I finally get it running.

This is all probably confusing, and I know that online is probably the worst way to diagnose an egine problem but I have never really worked on a ZR1 or any vete for that matter. Most of my experience is in turbo 4's, Porsche, and Modular Mustangs. I have learned a great deal from the ZR1 forum and net registry sites. Without you and these pages I would be completely lost.

The tach signal at the DIS diagnostic connector is great, the tach is broken at the cluster. It shows something like 4 to 10 times the actual RPM. Idle is 4000, when you blip the throttle a little is shoots past the gauge markings. This problem started before I took over ownership of the car.

The fuel pumps are working great. I run two 255 LPH walbro pumps. Why so much? To feed the wet kit of course. I have fuel pressure gauges that monitor pressure in the rail. It is ussually around 55 psi and it holds it for at least 15 minutes. I have removed the fuses for each pump and checked the fuel pressure for the individual pumps and they check out, about 52 psi each. I have also noid lit all of the primary injectors, they get signal. When I remove the plenum I get nice combustion out of all the intake ports, in sequence of course. I am stumped.

I am sorry to hear about the possible bad bearing. It seems that there is always something to fix. At least you will not suffer from having to much free time.

[Tyler Townsley]

OK, you have done more checking than I thought. Back to the MSD and the dis.

Put the scope on the dis output to the coils one at a time and see what the difference looks like with the ISS and the crank sensor. This signal should be the same in amplitude as you turn the knob with the ISS in the ckt. as you increase rpm the spikes get closer togeather but should remain the same. On the one dis I had when you got over 400 rpm the spikes became random in amplitude and regularity.

Can you look at the signal in pin E on the dis or pin F on the diag connector. This is the tach line and it should match your MSD, where do you tap in the msd and how does it account for waste spark? Could it have loaded the dis ckts taking out something internal in the dis? NOS huh, you and some guy I know in Denver would get along real well. LOL


Tyler

[8upZR1]

I will check the output to the coils today. The MSD is spliced in between the coils and the DIS. MSD has adapters where you remove the coils and place the adapter in between the coils and the base, with the adapter basically sandwitched between them. Each adapter has four wires running from it where you make connections with the MSD. Each coil has two wires and the adapter cuts these into four. The four wires are two that come from the DIS, and two that go to the coils. The MSD takes the signal that would normally come into the coils and changes it accordingly, more energy, retard, two step, multiple spark output, etc. Then it outputs the signal to the coils and controls them. There is a harness that attaches the box to these wires, and it also comes with a plug that can be inserted into the harness instead of the box. The plug just connects the cut wires again so that the ignition is back to stock. Swapping between the MSD and the plug makes no difference. The MSD figures the RPM from the coil input, the coil positive wire I think. Then it converts it into a standard square wave to drive a tach or what not. If the signal out from the MSD is 1800 rpm then the input is 1800 RPM. I have called MSD tech and they claim that it is impossible for the box to alter the signal. Input to output is 1 for 1. The box has settings for waste spark or coil on plug style systems. I have been running this box on my mustang for years and the vette for a few months before the head gasket failure and I think it is a great ignition. The only thing that compares is a boost-a-spark from Kenne Bell and it doesn't have any adjustability, it only increases spark energy, but the tradeoff is installation ease.

[8upZR1]

I have just compared the coils input signals from the DIS using the ISS and then the crank sensor. On all channels the signals are the same except for the frequency of the waves. The crank sensor, which is a lower RPM signal, has the same magnitude of wave as the ISS. The peaks are closer when I run the ISS. As I turn the ISS knob from crank to idle to cruise the peak to peak spacing decreases but the magnitude of the waves and their form stay the same as with the crank sensor. I checked again to see if everything was hooked up correctly and sure enough the crank end of the ISS was used with the creank sensor input of the DIS. It still gives me 1800 RPM in the Crank position. I think that maybe this is the problem. The DIS is not interpretting the crank input signal correctly. I have no way of measuring the rpm corresponding to the signal from the crank sensor, but it is definetely on the low side. I would say a maximum of 150 RPM. I dont know what the starter should be spinning the motor to but this seems low to me.