Another P0306 Misfire Problem

[CSR44]

96 5.7L 160K ran good until the fuel pump stopped 2 weeks ago. Replaced fuel pump with a Carter and the dreaded P0306 misfire showed up. Started reading up on this forum; checked fuel pressure, 60 psi with key "on" positioin, drops to 53 psi when motor is running. O.K., decided to put a Delphi pump in after reading about part store replacements. Same fuel pressure? Could the fuel pressure regulator be my problem? Truck misses at idle, but as soon as you accelerate it clears up and drives normal until idle again?

Here is a list of parts I threw at it so far:

-Fuel filter
-MSD 8.5mm wires
-Delphi cap & rotor
-AC Delco platinum plugs
-#6 injector poppet.

Thanks,
CSR44

[MT-2500]

Originally Posted by CSR44

96 5.7L 160K ran good until the fuel pump stopped 2 weeks ago. Replaced fuel pump with a Carter and the dreaded P0306 misfire showed up. Started reading up on this forum; checked fuel pressure, 60 psi with key "on" positioin, drops to 53 psi when motor is running. O.K., decided to put a Delphi pump in after reading about part store replacements. Same fuel pressure? Could the fuel pressure regulator be my problem? Truck misses at idle, but as soon as you accelerate it clears up and drives normal until idle again?

Here is a list of parts I threw at it so far:

-Fuel filter
-MSD 8.5mm wires
-Delphi cap & rotor
-AC Delco platinum plugs
-#6 injector poppet.

Thanks,
CSR44

Have you checked the cam shaft retard setting?

Good compression and plug and wire and dist cap and rotor?
Check or switch plug and wire on that cylinder.

Any codes besides 306?

Your fuel pressure is to low.
Yes could be pressure regulator.

But also check vacuum reading at idle and at 2K RPM and post back readings.
Guide lines on checking fuel pressure.
The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

[CSR44]

Thanks for Info MT, I will recheck the fuel pressure, but the funny part is that it starts great hot or cold, but after the initial start and the idle levels out, then it starts the misfiring?

[CSR44]

Update:

Replaced FPR and now the engine miss at idle is not quite as bad and it is now throwing a P0300 random misfire instead of P0306? Checked fuel pump again, 60 psi when you rev the engine, 53psi @ idle, block the return line and it reads 75 psi????? I am going have to wait until the weekend to check manifold vacuum.

[tblake]

You used new upper intake gaskets, right? Did you lube the electrical connector o-ring before slipping the UIM back on? It is possible it rolled over and is now causing a vacuum leak.

[CSR44]

Yes, new gasket on the upper manifold, I did not lube the connector o-ring, I will try to spray around the connector to check for a vacuum leak? The P0306 code is back again today.

thanks..

[tblake]

Yeah shoot come carb cleaner around.

Did you take a look at the #6 plug?

[CSR44]

Well, compression is reading 150psi, pulled rocker cover off, everything moving up & down as normal, I did the voltage test on the TPS, functioning normal.

I am getting ready to pull my hair out!

[danielsatur]

Do a leak down compression test on cylinder 6, instead of a regular compression test.
see www.youtube.com/watch?v=jG_RWs8ckp4
, Also
Do a smoke test for unmetered air leaks on your Inake,
see www.youtube.com/watch?v=FfiQ7qWiG-M

[j cAT]

Originally Posted by CSR44

Well, compression is reading 150psi, pulled rocker cover off, everything moving up & down as normal, I did the voltage test on the TPS, functioning normal.

I am getting ready to pull my hair out!

your problem if no codes would indicate a fuel issue..since you have a code this then means to me an ignition problem..

remove cap look for damage . plugs make sure they all look good same color ...measure resistance and carefully inspect plug wires for damage...

If you have the a/c refrigerent line running near the distributor cap water may have damaged the distributor/cap / wires etc...


above all DO NOT USE CARB CLEANER to find leaks ..this product is only for metal..when it contacts gaskets ,electrical wire, rubber in a short time it destroys it completely ...then you will start pulling your hair out !

the use of propane gas directed at suspected areas with the engine running will quicly and safely reveal the leak with an increase in idle speed ...this is the correct way to do this....simply attach a hose to a small propane torch then only allow a small amount of propane to come out the attached hose about 3 ft long ...if you allow too much propane this can cause the finding of the exact leak location to be much harder..

[tblake]

Originally Posted by j cAT

above all DO NOT USE CARB CLEANER to find leaks ..this product is only for metal..when it contacts gaskets ,electrical wire, rubber in a short time it destroys it completely ...then you will start pulling your hair out !

HAHA, I've always used carb cleaner.... Guess not anymore. Sorry guys. Bnaylor over on the Grand Prix forums usually gives me demerit points for bad advice. I don't have many to spair before I'm booted off apparently

But just wondering, would a bad poppet nozzel (fuel injector) also cause a missfire code to pop up if it is bad enough?

To the OP, you did observe both intake and exhaust rocker arms moving? As a rounded off cam exhaust lobe will show compression.

What does the plug look like? Wet with gas (ignition or mechanical problem), or dry (fuel starvation)? What type of plugs do you have in it? Have you just tried swapping one to see if maybe you have a bad plug?

[CSR44]

Tonight's update:

I was able to get my hands on a MT2500 scanner from a co-worker and did some playin around. One thing that doesn't look right is the Ignition advance is reading -16.5 degrees? I also read the same code P0306 misfire, but also P1345, which the scanner does not list any info on? Can someone tell me how to read the cam retard setting with this unit?

Thanks,
CSR44

[MT-2500]

Originally Posted by CSR44

Tonight's update:

I was able to get my hands on a MT2500 scanner from a co-worker and did some playin around. One thing that doesn't look right is the Ignition advance is reading -16.5 degrees? I also read the same code P0306 misfire, but also P1345, which the scanner does not list any info on? Can someone tell me how to read the cam retard setting with this unit?

Thanks,
CSR44

Ign advance is determined by VCM.
No problem with that advance reading if it changes withengine load.

Camshaft retard settings is usually in engine data or missfire data.
Depending on the cartage the scanner has.

What year and what cartiage do you have in it.

[CSR44]

I found the Cam Retard in the trouble shooting menu, this scanner has the Fast-Track 1998 module. My cam setting is (-5 deg.) I don't quite understand how the static ingnition timing at idle can be retarded (-16.5 deg.)? I'm used to the old school small block with 38 degrees full advance. I tried moving the distributor one tooth each direction, wouldn't start, so I guess the distributor was in the right spot when I did the intake gaskets 2 years ago. Now I need to figure out if its the cam pos. sensor, crank sensor, or maybe even worse, my lower intake gaskets sh*t the bed again!

[MT-2500]

Originally Posted by CSR44

I found the Cam Retard in the trouble shooting menu, this scanner has the Fast-Track 1998 module. My cam setting is (-5 deg.) I don't quite understand how the static ingnition timing at idle can be retarded (-16.5 deg.)? I'm used to the old school small block with 38 degrees full advance. I tried moving the distributor one tooth each direction, wouldn't start, so I guess the distributor was in the right spot when I did the intake gaskets 2 years ago. Now I need to figure out if its the cam pos. sensor, crank sensor, or maybe even worse, my lower intake gaskets sh*t the bed again!

-5 degrees is boder line.

The dist needs to be turned a little to bring the camshaft retard setting to as close to 0 degrees as you can get it.

Then recheck for missfire code and get the scanner readings on how many times it is misfiring.
Post back if just a few or full time miss.
Can you feel engine miss?
Your fuel pressure readings is low.

Rerun the full fuel pressure test andf post back readings.