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Discussion Starter · #1 ·
Okay, I have been searching all over the web for info and the shop working on my truck is stumped. Let me explain what is happening and what has been done so far to try to correct the problem.

I have a 2001 S10 with the 4.3L Vortec and the auto tranny. The other day after running some errands the truck started to misfire and skip. I had only driven about 40 miles total for that day and the truck ran fine early in the day. It seemed the more I drove, the worse it got. I got home, hocked up the scanner and got the generic 0300 code for “random misfire. Frustrated that I could not figure it out, I shut the truck off and went inside for a bit to see if I could look up some info. 20 minutes later, I went back outside and cranked the truck up[ and it ran just fine. I cleared the code for the misfire and let the truck idle for a few minutes. Sure enough as the truck warmed up, it started skipping and if you hold the accelerator at a certain point like cruising rpm’s, she will really start to sputter and cough.

The following day I took it to a friend’s shop and after three days, they could not figure out why when it got warmed up, it would start to run like crap. They replaced the cap and rotor even though I had just done that 6 months ago, but still the misfire was there. They said the misfire was on the right bank most of the time but occasionally it would misfire on the left, but not often. I decided to take it home thinking maybe it was bad gas (at this point, I was just guessing). It got so bad driving now; it was blowing black smoke out like a diesel when I would try to drive it. I searched the web and found some articles about the spider injector assembly and figured that had to be the issue. I dropped it back off to the shop and they replaced the CSFI spider injector with the new MFI upgrade from Delphi. They also replaced the intake gaskets as they were leaking coolant at the water passages (nothing major, but figured it should be taken care of while getting the MFI replaced).

Well, even with a new MFI injector assembly, new plugs, new cap, new rotor, new intake gaskets, the truck is doing the same thing, when it warms up, it throws the 300 code and starts skipping badly. It is misfiring from the right bank with an occasional misfire on the left. When it first cranks up, it runs great, but as it warms up, it gets worse the warmer the engine gets.

Here is a list of things that have been fixed on the truck over the last six months so everyone can see what has been done…

Cat was removed 6 months ago
Both O2 sensor banks were replaced about 6 months ago
Fuel filter was replaced about 9 months ago
Distributor was replaced 6 months ago
Cap and rotor have been replaced 3 times in the last 6 months (counting today)
Spark plug wires have been replaced about 6 months ago
Spark plugs have been replaced twice in the last 6 months (counting today)
Vacuum hoses were replaced 9 months ago
CSFI replaced to MFI today with all corresponding gaskets and O-rings
Intake gaskets replaced today
No other codes are present and they have a very expensive scanner computer that will tell them even if a sensor is within spec, but showing signs of weakening.

Does anyone have any suggestions? Why is the truck skipping on one side and not the other and only when the truck warms up? They are going to do some more extensive testing like compression check the cylinders, check fuel pressure (though can’t see that causing a skip on one side). I saw some posts about maybe the crank sensor, so could that cause this issue?
 

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A *new* distributor installed?

Have you checked fuel pressure while driving and missing?

I've also seen a GM bulletin about valves sticking in the guides and causing a misfire.
 

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The shop should have done a fuel pressure and leak down test.
Pressure should be 60-66psi key on engine off, and should not drop below 55 psi for 10 minutes.
Did they use AC Delco cap and rotor?
When talking about right and left of the engine, use bank1 or bank 2 instead.

Are the plug wires properly installed on the cap for bank 1 (3, 1, 5)


Have them pull the crank sensor and check it for scuffing from the crank reluctor. If there is scuffing on the sensor, replace it and have it shimmed.
A crank relearn has to be done afterwards. That year of engine has been known to have problems with that.
 

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Discussion Starter · #5 ·
The shop should have done a fuel pressure and leak down test.
Pressure should be 60-66psi key on engine off, and should not drop below 55 psi for 10 minutes.
Did they use AC Delco cap and rotor?
When talking about right and left of the engine, use bank1 or bank 2 instead.

Are the plug wires properly installed on the cap for bank 1 (3, 1, 5)


Have them pull the crank sensor and check it for scuffing from the crank reluctor. If there is scuffing on the sensor, replace it and have it shimmed.
A crank relearn has to be done afterwards. That year of engine has been known to have problems with that.
Plug wires are in the correct positions. Yes, they used AC Delco cap and rotor, which was also used the time before too when it was running fine.

The crank sensor idea and the sticking valve post are nice suggestions I will let the shop know tomorrow when I go by there to check on things. I am going to make sure the do the leak down and fuel pressure check as well.

Thanks everyone for the input so far and I appreciate any other suggestions as well. :)
 

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Discussion Starter · #6 ·
Well the first shop has thrown in the towel and given up. The truck is at another shop down the road and is not happy with what the first shop has done so far.

I did finally get the first shop to run more tests before they gave up. They did do a compression chck and though I don't know the numbers, they said all of the cylinders were well within spec. The checked the fuel pressure and did a leak down test...everything checked out there as well. I had them replace the plugs and the plug wires just to eliminate that since they already replaced the rotor and cap. They even replaced the crank angle sensor and tried another computer. Still giving the 0300 code, but now a new code popped up the the other shop thinks is the problem...

I can't be sure of the code number as I did not write it down, but it was a lean fuel mixture, Bank 1. After the "new" shop research that a bit, they feel the intake gasket that the first shop replaced while doing the spider injector upgrade are installed improperly and there is a serious vacuum leak on the bank 1 side. Unfortunately the first shop tried removing the EGR valve in thier testing and blocking it off (of course this was not going to be the problem) and left the harness laying on the belt, so now I have to go to the junkyard tomorrow and get another plug and 4 inches of wire for the EGR valve so that the second shop can do his proper diagnostics on the engine.

If I find that it was the intake gasket that is continuing this issue because the first shop can not install it properly, I am going to be so pissed. The only reason I left this to a shop to do is because I am super busy right now and I needed my truck back in a couple of days and did not have the time to spend to fix this myself, which at this point, I could have easily done.

I am thinking the original problem was the spider assembly and the problem now is a badly installed intake gasket. I will let yall know what the verdict is next week when I should get my truck back (now going on two weeks!) Grrrrrrr!!!! :(
 

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Have you checked fuel pressure while driving and missing?
I've also seen a GM bulletin about valves sticking in the guides and causing a misfire.
Have the shop drive your truck with a scanner on it. Have the scanner monitor the O2 voltage, both banks if possible, or at least the one with the most issues.
Have them go WOT under load, up a steep hill if possible.
The O2 voltage MUST be over .9 volts.
If it is less the engine is NOT getting the fuel it needs, it is going lean.
This can be a fuel pump, restricted line or a bad fuel regulator.

Ideally this can be done while the engine is acting up, it may not show up otherwise.

My 95 Jimmy showed spec fuel pressures while sitting still, only when driving for a while did the fuel pressures drop. The engine needs more fuel while driving than sitting stationary. A driving fuel pressure test is the most real-world test.

The above test can be done in a few minutes and without getting their hands dirty. This test will absolutely confirm yes or no to fuel supply problems.

If this tests out then consider the GM TSB. More difficult and expensive to confirm. If it was my vehicle and I suspected the TSB could be the solution. I would do a crankcase flush and use a good grade oil and try it.
 
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