[badasgmc]

Hi, New member and first post. I have a 96 Yukon 5.7 liter. Drove it home from work two weeks ago and everything was fine. The next day i go out to start it and all it would do is turn over, and when releasing the key you could hear a sputter from just one cylinder. I then try and start it the next day and fires up with some hesitation, very rough at a low rpm and clears up and runs fine after revving it a few times. I drive it for the next week with no problems. I go to start it the other day and same thing, wouldn't fire except a random cylinder with built up fuel when key is released.

Now to bring you up to date on parts replacement and tests. Fuel pressure is 62 psi when key is first turned on and pump runs for 2 seconds. The fuel pressure then drops to 54 psi when pump stops running for the first 2 seconds. Not sure what the fuel pressure is when the engine is running since it wont start. I have spark at the coil wire and spark plugs, but maybe a little week. Could the coil be going out but still have a week spark? Replaced spark plugs after checking and they were fouled out with gas. Replaced fuel spider (CSFI) with a new unit. Did a compression test on all cylinders with the highest cylinder at 180 and the lowest at 159.

 

[84fiero123]

My guess would be ignition module, if this has a distributor it’s under the cap. If this has a coil pack, it’s under the coils.

Under the distributor it’s a part costing less than 50 bucks.

If it’s a coil pack it is very expensive.


The module in our 94 went and then worked, then went and then worked, they can be quirky.

There is a test procedure but I can’t remember it.

 

[badasgmc]

Thanks for the reply. I just got back from the local Napa with a new ignition module ($125) and coil ($50). Going to give it try and see what happens......going to suck if it isn't either after spending $300 on a new CSFI unit.

 

[LANDBARG]

Holy crap!! $125 for an ignition module?!?! I can get the whole distributor with the coil in it for $100!!! For your sake, I hope that is the fix. Are you getting spark at all when you diagnose?

Thanks for the reply. I just got back from the local Napa with a new ignition module ($125) and coil ($50). Going to give it try and see what happens......going to suck if it isn't either after spending $300 on a new CSFI unit.

 

[kirk.toune]

What was the outcome?

Just wondering if you had anything to report from the replacement parts you described? I am having a very similar issue with mine. Please tell us what happened? Thanks..

Kirk

Thanks for the reply. I just got back from the local Napa with a new ignition module ($125) and coil ($50). Going to give it try and see what happens......going to suck if it isn't either after spending $300 on a new CSFI unit.

 

[armand71]

Have you checked any of your temperature sending units (temp. sensors)? I know it sounds a little nuts but I have seen that problem quite a few times. I've seen them showing -45 degrees at room temperature, which would tell your ECM or ECU or whatever you call it, to dump so much fuel in that it won't start.

 

[badasgmc]

To bring everyone up to date on the post, the truck is now fixed. Turns out that it was the distributor cap. Its the style of cap that the terminals of the cap are on each side of the cap for the even and odd cylinders. The mechanic said that they are prone to cracking around the coil terminal and cant even see when they are cracked. The way the cap is made with the strips of metal embedded in the plastic of the cap and overlapping each other it is very susceptible when cracked for crossfire. I also had the timing chain replaced it was getting a little sloppy with 170 on the odometer. Lesson learned, a very expensive lesson at that.