2003 Chev S10 - 4.3L P0300 Troubles

[pitcrewllc]

Any advice or help with this vehicle would be much appreciated.

2003 Chev S10 4.3L VIN X

Vehicle came in with a complaint about an intermitant missfire/idle rough/lack of power.
The vehicle had 92k miles on it with original spark plugs, cap, rotor, wires.
The only trouble code present was P0300.

We intially thought it just needed a tune-up so we suggested that to the customer and he authorized the work.

Intially we changed just the plugs and wires and the miss was still there. We then changed the cap and rotor, this also had no effect.

We noticed that the exhaust from the vehicle had a distinct odor to it, it smelled sort of like sulfur but not exactly.
Also when revving the vehcile a large amount of a greyish color dust is coating the floor and wall next to the tail-pipe.

We thought that the catalytic converter may have plugged so we disconnected the exhaust from the manifolds. This did not chage the missfire at all.

We then checked the fuel pressure and it is normally around 54-56 PSI with the engine running. We went ahead and pulled the fuel filter off (it was original never changed) and it was hard to blow through so we changed it as well. This didnt help a bit either.

We ran the injector balance test using our Snap-On Verus and each injector drops the pressure from 54psi to 38psi when activating each one.

Missfire Monitor shows the majority of the missfire on cylinders 3 & 5. Spark was tested at those cyclinder with a spark tester and was found to be ok. Compression was also checked and found to be ok.
Component tests on MAF and MAP test ok.

The only thing I see out of whack on the datastream is the ST Fuel Trim on Bank 1 it hangs around 25.




Any help with this would be much appreciated.

[brianp87]

I would pull the # wire off and see if rpm drops. same with # 5. To confirm that its isolated to those cylinders. I would alos be looking for a vacuum leak or possibly worn distributor.

[liljoe]

The flow rates on the injectors seems to be a bit too varried, I would be looking at that and the valve train, intake system for carbon and/or restrictions.

[pitcrewllc]

Pullling a wire off of cylinders 3 & 5 make no difference to rpm.

The flow rates of the injectors all were the same each injector would drop the PSI from 54 to 38 when activating.

I cant help but think that this problem is related to the spider injection unit.

[brianp87]

I would still suspect a vaccum leak or distributor

[steven kiser]

may well be an issue with the spider.

[brianp87]

may well be an issue with the spider.

Could be i looks for clean washed areas under there. If it is I recomend doing the hoses going through also

[steven kiser]

another quick thought here is a leak between 5 and 7 cylinders. i would try a quick leak down test. with both plugs removed charge one with air and see if it leaks out of the other plug hole. probably a waste of time but i've seen issues like this.

[CRAIGISH]

I had one with a simular problem. What we found was a intake valve was intermettantly sticking open. We used a bore scope through the spark plug hole and found it was open on the exhaust stroke. We tried to take a picture of it with the camera on the scope but it snaped shut before we could. Hook a vaccume guage to it and see if the needle bounces excessively.

[Tim Martin]

For me, the clue is the Short Term Fuel Trim number at +25. This is also the maximum added fuel possible. So, as I see it, the ECM thinks it got us a lean running situation that needs to be corrected so it adds injector on time. Am I right so far? So, it could have a vacuum leak to those cylinder runners. It could also be injectors sticking for whatever reason. However a injector running test should a ruled that out. I lean towards a vacuum leak. If I recall correctly, the brake booster and PCV valve both draw from that area of the intake manifold. I'd also scope the O2 sensor.

hth

[Ruger77]

We used to start our diagnostics with a vaccuum gauge, now it seems like a last resort. Not picking on anybody, just not sure why we (I) over-think things.

[Tim Martin]

Ah ha. Now he is showing what age bracket he belongs in. I have seen some a today's techs not even hardly know what a vacuum gauge is and what all it tells us. For myself, I assume that by the time a guy posts on this forum he already has done some o that basic stuff.

[steven kiser]

may well be an issue with the spider.

Could be i looks for clean washed areas under there. If it is I recomend doing the hoses going through also

kinked a few of those myself

[steven kiser]

We used to start our diagnostics with a vaccuum gauge, now it seems like a last resort. Not picking on anybody, just not sure why we (I) over-think things.

i totally agree. years ago it was just check the basics. fuel/air, compression, spark, exhaust. now it sometimes feels that the stars and planets have to align, st peter has to blow the golden bugle and the cubs have to win a world series before you can hook up a scanner and discover that the key reader isn't working and someone filled the tank with water. seriously, i remember being able to sit on the inner fenders or stand inside the engine compartment while working on the engine. i thought taking the side plate off the inner fender on a chrystler with a slant six to easily service the distributor was a pain in the breeze way. i was ready to quit when toyota's showed up until i convinced myself that they were just a passing fad. i was disgusted when i opened the hood of a g.m and saw the vacuum hoses and the check engine light. what are they going to think of next? i should have remained a truck driver and a member of the teamsters. now i yearn for those days.

[Tim Martin]

steve, you be funny. Ya really want to go back to those days? Not me. We are havin too much fun in this business. I just wish it paid a little better.

[vinnieg]

We just had a similar problem with a 1997 GMC van with a 5.7. It came in with an intermittent miss the customer described as a violent "shudder" when pulling out in traffic. Naturally we were unable to duplicate the violent shudder, no codes came up, etc. 292K worth of neglect on the engine but it was still running.

After replacing a leaking fuel pressure regulator, worn out distributor, plugs and wires there was still a problem and now it sets a code for lean bank 1. Compression good and when I hooked up my old Snap-On Tach Dwell with cylinder kill and balance we determined that cylinder 1 was still dead. Turned out the injector was bad even though it passed all the balance tests with the scanner. This is the spider with replacable injectors and it turned out the solenoid portion worked fine and that is what the scanner tested. The injector poppet on the other end wasn't opening up. We pulled the spider, ran some more tests and confirmed there was no fuel coming from that injector. (Might coulda cranked it with the spark plug out and check for fumes but...)

In short, all the test equipment did was lull us into a false sense of accomplishment. It all boiled down to the old Mark I eyeball in the end. The tech and I are both big on "Back to the Basics" when it comes to troubleshooting but this time a we bit of anal-cranial inversion resulted in us not starting all the way back in the basics. Felt like we were hot on the trail of success and instead ending up with teeth marks on our behinds.

I vote checking the injectors on this problem and if you have to pull the spider and test them all to see how much difference there is.

Max (Chastend after a week of losing money on that van.)

[vinnieg]

steve, you be funny. Ya really want to go back to those days? Not me. We are havin too much fun in this business. I just wish it paid a little better.

Points, condensers, carburators... It wasn't drivability so much as understanding what everything was supposed to be doing. I miss those days too but not too sure I want to go back to them unless I can do it at todays labor rates.

Max

[steven kiser]

i'm not sure if cranking it with the plug out would give you an answer. i think that the poppet in the end of the tube is activated by the suction of the piston going down. the main injector fires and pretty much charges all the lines.

[vinnieg]

i'm not sure if cranking it with the plug out would give you an answer. i think that the poppet in the end of the tube is activated by the suction of the piston going down. the main injector fires and pretty much charges all the lines.

Steve,

Just for future reference it the poppet at the end of the tube will open but it is a little tricky to get there at first. Keep in mind we were using a Snap-On brick scanner and a Modis. In our case we had all the poppet tubes pulled and laid across the top of the engine. After priming the pump and trying to select each injector we got no response for a while until the tech accidently bumped the scroll wheel on the brick. The scroll wheel activates the solenoid and if you are sitting with pressure on the system it will give you a highly visible spray pattern. (No Smoking is recommended during this test.)

The scroll wheel activation step was the only part of the procedure that was not documented in the menu which is why the tech discovered it by 'accident'.

Looking back we probably could have viewed this through the spark plug hole but since we already had the poppets pulled...

Hope this will help someone else and save some of the time and aggravation we went through.

Max

[crmeyers]

Had a 4.3l with a similar problem...turned out to be a small "rock" of carbon stuck in the EGR pintle. Pulled the EGR valve, cleaned everything up, did a air induction cleaning and PRESTO...fixed. It did not throw an EGR code, just a P0300. Might want to visit that one if all else fails...Good luck.