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  #16 (permalink)  
Old 04-21-2013, 08:08 AM
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One thing to consider is a misfire needs to be fairly bad before you can feel it. The computer can pickup misfires that you may not feel while driving the vehicle so done assume you don't have one. The sad part is a lot of these "mechanics" try to troubleshoot a problem like this and they don't have the correct equipment. A trained mechanic and a hand held scope and a 5 gas would have help identify Brian's problem and proved there was no real misfire. The test would have taken 10 minutes and identified this as a mechanical issue.
being able to look at the exhaust gas makeup is like a blood test for a doctor when you are sick.
People go to the dealer because they think they are smarter than a non dealer mechanic. The truth is that it is usually just the opposite. If they haven't seen it before or their scan tool doesn't see the problem then you must not have one.

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  #17 (permalink)  
Old 04-22-2013, 06:25 PM
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Yea I had an exhaust gas test. Actually I just took the van into a state emissions station. Their print out is pretty in depth, and I know enough to
"read" this blood test. The exhaust was as clean as could be. Thats when I realized there was no misfire. I provided this info to chevy, but obviously
they didnt consider it info in their diagnostic. To be a great mechanic, one has
to think abstractly, and not just by the book.

It seems like hit or miss.
And man I would like to find a good mechanic here in Atlanta. The search continues.
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Old 04-22-2013, 09:33 PM
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You may have a faulty reading 0'2 sensor, not bad enough to set a code, but off enough on it's return voltage to lean your engine out enough to set a code.

Do not over look a exhaust manifold exhaust leak either.

Working on car's emission's has gotten tougher here in California. Now it includes diesel truck's. OUCH
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Old 04-24-2013, 08:23 AM
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Brian,
We have now replaced all main bearings, thrust was good, and replaced distibutor with New AC Delco unit. It made no change. Check engine light flashes when rpm is raised beyond 1500, P0304. I also cleaned the MAF. When the heads were removed the no. 4 piston was much cleaner than all the rest, if that helps.
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Old 04-24-2013, 09:17 PM
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what year and engine are you working on? Is the engine running well, but setting misfire codes? Or is it running poorly?
your doing a hell of a lot of work.
my van had exactly the same problem. it plagued me for two years.

you may need a correlation relearn performed by chevy, though that never worked for me.

When I first got my fancy $300 AC delco distributor, accidently installed the distributor one tooth off.
the engine ran, but registered misfires -flashing check engine light. i pulled it out and reinstalled, and the misfire code cleared. so check your distributor.

also, the crankshaft sensor is very sensitive. if it is too close or to far from
the reluctor wheel, it wont read correctly. chevy put shims on mine to get
it in specs, ...... but in the end that did not solve the problem. chevy said īts fixed", and I got about a mile down the road and then the flashing check engine came back! check the crank sensor. make sure its torqued in correctly, and make sure the front engine cover where the sensor is is not damaged.

have you checked your compression? low compression on a cylinder would definitely set a misfire code.
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Old 04-24-2013, 09:19 PM
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carsavycook is also right. check for manifold leaks and old o2 sensors.
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Old 04-25-2013, 12:43 PM
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This engine is equiped with a multi pin plug behind the throttle body. The fuel injection system is located under the upper intake plenium, which is not difficult to remove. It has a 'plastic' 'lined' injector system, with a fuel pressure regulator.

The o'ring's on the injection nozzles can fail, and the pressure regulator diaphram will also rupture causing a fuel to leak into the lower intake manifold.

With the upper plenium removed, cycle the ignition key on, and off twice, and look for a fuel leak.

Hope this help's.

Stephen
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Old 04-25-2013, 09:05 PM
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could one look for these leaks using a fuel pressure guage?
without taking the upper intake off. Would this manifest as
low fuel pressure at idle?

I have had several of the csfi engines, and the csfi units have held up
well over many miles and many years. I removed a unit from
my 2001 van with 150K miles. The rubber and the regulator were still
in really good shape. I upgraded to the new direct injection system.
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Old 04-26-2013, 03:04 PM
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This is a pic of the reluctor that is read by the crank position snesor, except the V6 only has 3 vanes instead of the V8's 4.



Here is a pic of a "knife-edged" distributer gear that can cause missfires when all else checkls out of teh Vorte engines.




Top is the stock CSFI and bottom is the MPFI GM conversion, obviously the V6 versions have 6 spiders legs. 2003+ V6's use the MPFI conversion spiders from the factory/ The MPFI conversion spiders flow the same amount of fuel but they have Multec 2 mini-injectors at the end of the spiders legs, instead of poppet valves that open by fuel pressure on the CSI spiders.


Here is some GM info on cleaning the poppet injectors, as well has some GM bulletins on spider service
http://www.acdelcotechconnect.com/pd...sb_05D-105.pdf

Stock pressure should be 60-66psi, KOEO(Key On ENgine Off) the fuel pressure regulator will bring down the pressure at idle or KOER(Key On Engine Running).

peace
Hog
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Old 04-26-2013, 06:46 PM
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The poster has already replaced the dizzy with an ac delco.
Apparently the gear metal is soft and wears rather quickly.
I replaced mine with a $99 reman. It totally did not work.
It had so much free play that it would not stay even close to proper timing.

I have a suspicion that the poster installed the new distributor one tooth off.

So if the stock fuel pressure is running lower than specs, should I suspect
leaking poppet nozzles. I have a 99 s10 with 115K that just started reading
p0304. It has new plugs/wires/rotor/cap, low miles, and is otherwise in great shape. I have not looked into it yet, but should I suspect the 14 year old
poppet nozzles? I already upgraded the csfi on my 2001 express, but like I said before, I never had any issues with the poppet nozzles.

One more question. I kept the csfi unit for parts or to sell. IS IT WORTH SELLING, or should the csfi always be replaced with the direct injection?
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Old 04-26-2013, 07:18 PM
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Quote:
Originally Posted by ffroese5 View Post
Brian,
We have now replaced all main bearings, thrust was good, and replaced distibutor with New AC Delco unit. It made no change. Check engine light flashes when rpm is raised beyond 1500, P0304. I also cleaned the MAF. When the heads were removed the no. 4 piston was much cleaner than all the rest, if that helps.
The clean piston is indicative of water getting into the combustion chamber. Could be a small crack in the intake port behind the valve
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Old 04-26-2013, 07:20 PM
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Hogg....nice picture of the distributor gear. I have seen them worn less and cause the problem.
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Old 04-27-2013, 07:57 AM
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Quote:
Originally Posted by briansansone View Post
The poster has already replaced the dizzy with an ac delco.
Apparently the gear metal is soft and wears rather quickly.
I replaced mine with a $99 reman. It totally did not work.
It had so much free play that it would not stay even close to proper timing.

I have a suspicion that the poster installed the new distributor one tooth off.

So if the stock fuel pressure is running lower than specs, should I suspect
leaking poppet nozzles. I have a 99 s10 with 115K that just started reading
p0304. It has new plugs/wires/rotor/cap, low miles, and is otherwise in great shape. I have not looked into it yet, but should I suspect the 14 year old
poppet nozzles? I already upgraded the csfi on my 2001 express, but like I said before, I never had any issues with the poppet nozzles.

One more question. I kept the csfi unit for parts or to sell. IS IT WORTH SELLING, or should the csfi always be replaced with the direct injection?
I would keep teh CSFI spider for parts. Having done so personally has gotten me out of a jam before. If its good there is no sense swappinmg to the MPFI spider, but GM did start installing them in the 2003 V6's for a reason.

peace
Hog
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