Hello all:

It has been a very long time since I've posted here. I have (however) been keeping an eye on the forum for the various projects that I have done on the 93.

So - the car - 93 LT1 (lightly breathed on)/ZF6 coupe: will not start - exhibiting symptoms of "out of gas" when there is clearly a LOT of gas in the tank.

A few weeks back, I took the car out on a decent evening; clear weather October evening. I had it on the highway, approaching my exit, and I hit the accelerator with intentions to shoot down the ramp. Instead of the surge of power I was expecting, the car bucked and sputtered as if I had run it out of gas. Looking at the gas gage: It showed I had over 3/4 tank (more on that later) so: I down shifted and attempted to hit it again and the car stalled, leaving a SES code on the DIC just before it stalled. I tried to start it a few times, and could not get it to start again, and later that evening I succumbed to the "tow of shame". Knowing that the car's history: I immediately thought that my fuel pump was done. ... so (before putting a pressure gage on the rail) I figured that I would replace the pump along with associated *stuff".

Before actually replacing the pump, I checked the pump fuses and verified that they are good.also verified the connection is good, and hit the fuses with some dielectric grease.

Now I have replaced the pump, strainer/sock, sending unit gasket, sending unit bolts, and so-forth; and I can clearly see that there is a LOT of gas in that tank.

Still, I have no start. So, I busted out that fuel pressure test kit that I should have pulled out weeks ago, and connected it to the rail; thinking that I may have a problem with the fuel filter, but - because I replaced it about 10 years and less than 10k miles ago, I was suspicious of what I would see.

Last night, I put the gage on, and got 42-43 psi. Bled the pressure, tired again. 43psi. I was puzzled but intrigued: so: I left the gage on the fuel rail after trying to start it another couple times (no luck) - and saw similar readings (bled pressure every time between start attempts).

Next, I figured that I may have a "holding pressure" issue or maybe a fuel volume or an injector issue, so: I floored the accelerator and tried again: still exhibiting conditions of a car that sounds like it is out of gas. Bled pressure, and tried one more time and got about 42psi, and wanted to see what the pressure would do over night. This morning I woke up, checked the pressure: 40psi.

Next plan(s) of attack:
I will get a resistance reading on the injectors.
I will verify that I am getting spark
I will look at the front of the intake to verify that I am getting air.

Any other common items that I should consider? Plugs are less than 10 years old, as are wires (taylor 8mm) seem to be in good condition. I think something a bit deeper is our issue.

 

Fuel pressure at the rail is at a tiny bit above 36psi, after having let the project sit since last night. I estimate that it is holding pressure just fine, and there is not any issues with the fuel passage from the tank up to the rail, and back ... based on what I know so far.

I do not have another pair of hands to give me a hand at verifying that we have spark; so that will have to wait another day.

 

Verify that the injectors are firing with a noid light or 12 volt bulb.

 

I could not see anything out of the ordinary in the engine bay while I looked around, and tested the resistance of all 8 injectors. (below are my findings, by cylinder number)

1= 11.9
2= 11.9
3= 11.8
4= 11.9
5= 12.0-12.1
6= 11.9
7= 12.0
8= 11.8



All measurements are in ohms (obviously). This value seems a tad low versus the "typical" values that are supposed to be in the LT1, but I am a bit apprehensive that this is my 'issue' because when I try to start the car, it seems that it will get SOME fuel, and possibly run (though it has not since it died), but I do not know what low resistance values (on the injector) would do to the running condition of this motor. For the sake of curiosity, I pulled the air intake, and made sure that the TB was moving OK, and could smell gas when putting my nose to the TB opening. ...while not a scientific test: I am thinking that it is getting fuel.

@JimLentz - can you please expound on how to set up this injector verification test you are describing?

 

Check for codes?

 

Take a connector off one of the injectors and when you crank the engine 12 volts should pulse as that is what triggers them. Your resistance on the injectors is pretty good. When I checked mine one was 4 ohms so I replaced them all.

You could also spray a shot of starter fluid in the throttle body and if it starts for a second or two you know it is fuel related.

 

I betting there is no spark.
You need to check for spark off the coil and at a plug.

Could be the ICM, opti or ECM.

If there is no spark, you need to measure the drive from the ECM to the ICM. If there is drive, ICM can be defective.

Check injector drive with noid light. If good, ECM and opti are basically functioning.

Depending on results of testing will give you a direction rather than guessing. If you find something missing, post it if more help is needed.

 

Brilliant .. as he stated.

 

Check the fuel pressure regulator, pull the vacuum hose off of it and see if it smells like gas. If it does replace it and check your oil to make sure it's not diluted with fuel also.

 

Have you checked for a spark? The optispark is known for failing .

 

I was finally able to get into diagnosing last night. I also had an extra pair of hands to help; so I went at it pretty deep.

With my inductive timing light, I found (when attached to any one of the 8 spark plug wires) that there was spark, but intermittent (ie: it did not light the timing light with any regularity or strobe pattern).

Curiosity set in, so I tried on 6 of the 8 wires and got the same result. (the timing light would flash, but a bit erratically - not with any pattern like the "strobe" effect).

Next, I shot a tiny bit of ether into the intake/TB: tried again. No start.

All the while: I had the fuel pressure gage connected, and the pressure never really wavered it was 38psi after start, around 40psi while attempting to start.

Next: I pulled a connector off of #3 injector and had my buddy hit the starter while I was under the hood with my fluke to check for the 12V (DC) pulse. As the starter was running, the connector had a (one) time that it hit a little over 12V, but then it danced around in the 0.2-0.3V range while the starter was running. I pulled the injector connector on the #5 injector and got the same thing: a little over 12V one time, but then danced around in the 0.2-0.3V range while the starter was running.

I also pulled the vacuum line off of the fuel regulator and it did smell like gas, but that is anecdotal at this point ... I do not believe that it has anything to do with the inability to start.

So that we can give a little brief history on this car:
The plugs and wires are from 2002 era; when I changed the opti-park.
The car does not get much time on the road, I have about 15k miles on this opti, plugs and wires. The opti I bought (back then) was a GM unit.

While I cannot rule out the opti as our root cause, I am leaning toward ICM, but I would like to know if there are any simple tests I can perform to test the 'drive' between the ICM and ECM while attempting to start.

Also: any other comments/suggestions are appreciated.

 

To measure output from ECM;

Ignition key OFF, remove Ignition Module connector.

Set meter to read AC volts and connect probe to terminal B, (white wire). Have someone crank engine, meter reading should be between 1 to 4 volts AC. If you get it, the opti and ECM are probably working OK. If the voltage is there, the ICM (or coil) could be defective.

You might have intermittent and weak spark. Have someone crank it and hole a plug wire near ground. There should be a 1/2 inch bright white spark.

 

I was able to get under the hood last night and had an extra pair of hands to help.

First up:
the ICM connector was pulled, and I took some measurements (VAC) while cranking (...terminal B voltage and connected the black Fluke lead to the black wire that is assumed to be ground).

Test 1: we had 1.2-2.8 VAC while cranking
Test 2: we had 1.3-2.9 VAC while cranking.

During the cranking: the voltage was bouncing around quite a bit, there may have been a 3VAC hit at one point, but it was quite a quick fluctuation/dance that I saw while cranking so - I think that we've confirmed that the ICM is receiving the correct signal (from the ECM and opti). However, I am not sure we can rule the ECM and opti out.

I saw that the fuel pressure remained solid at 35-39 PSI during the cranking/testing.

Next up: I reconnected the ICM connector and I pulled the two - piece electrical connector on the coil.

I tested the resistance on the coil on the 4 input
That is where I saw some slightly bizarre behavior.

I tested the resistance left to right and top to bottom.
(both measurements the same regardless of the direction/polarity of my fluke wire connections).
On the left side (top to bottom) 0.5-0.6 ohm
On the right side (top to bottom) 0.4-0.6 ohm

Then:

Bottom: Left to right = -1.0 ohm and right to left = 1.2 ohm
Top: Left to right = -0.5 ohm and right to left = 1.0 ohm.

I have no idea why there would be a negative resistance; and I do not know what these values should be. Could this be a problem related to the coil?

 

I had a few minutes to do some work on the car today. I pulled the ICM connector, threw the key on, and confirmed the (DC) voltage on the A and D terminals. With the key on, I have 11.32V (to ground), on both the A and the D terminals.

I also attempted to pull a code, if there was one that was stored on the computer. I was only able to get the "C12" read out on the speedo display, it went through the normal 3 code cycle; and it did not reveal any codes that were stored. This may be because I have the battery on a "quick shut off" switch, and every time that I am going to garage the car for more than a week at a time, I use the "quick shut off" switch as if I am disconnecting the battery.

Now that I think of it .... is it possible that this (battery quick disconnect) is what is causing issues with the car? I can't imagine that would be our culprit.

 

If your only reading 11.32 volts you got a dead battery or a short in the ignition wiring. These cars don't like low volts.

 

Hmm.

I appreciate the idea that this car will need 12V at the ICM - but I do not believe that this is a dead battery (it cranks just fine!). That would lead me to believe that we have a potential short in the ignition system (specifically in the wiring thereof). However when it first failed, it was kind of immediate: I would think that the root cause would be standing out a lot more.

I am still a bit suspicious of the coil. Measuring the resistance ... where? I do not believe that I confirmed anything by measuring pin-to-pin resistance.

 

Ok fellas, I did a little more testing, and I have confirmed that I do have a solid ground going over to the ICM.

Now for how to test the coil spark output. That's on the list for tomorrow. To test: I'm going to put the inductive timing light on it, and turn the key to see if I am getting spark from the coil over to the opti... I still cannot rule out the opti even though I am seeing the proper voltage at the ICM both with ignition on, not running (supposed to be above 10V) and the VAC is happening properly (from what I can tell) when cranking. Any other suggestions here? What I am seeing so far is leaning me toward coil or ECM; both easier to replace than the opti in theory.... but I would like to nail this down and rule out whatever I can.

 

I believe that we've narrowed it down to the coil.

Here's why (the following is the steps I took today):

Coil wire (to opti) = 361 ohm resistance (puzzling, but I do not believe that this is our culprit because we're passing a fair amount of voltage and it is a 8mm taylor wire with a lot of insulation, I would have thought that this would have like -0- resistance, but I saw similar resistance when I did the same test on the P-car).
Connected the inductive timing light to the coil: cranked the engine ... no spark.
Pulled the electrical connector from the coil, turned the key position to ON - and I confirmed that I have 12.2V to the lower right pin (passenger lower) on the electrical connector.
Removed the key from the ignition. Tested resistance from the coil input electrical connection to the coil output pin and measured the resistance: every one of these electrical pins to the coil output pin ... 97 k-ohms. I *believe* that we are supposed to have 5-7 k-ohms here. With that, I will be looking at replacing the coil as my next step.

Any other suggestions from the others who are following along?

 

Try this put a T pin or pin probe through the insulation of your red wire coming from your icm hook it up to a test light and the other end to ground crank the engine the light should flash not stay on steady . If it stays on steady you have a bad icm.

 

This video by "The Master" may help !!