Runs Rough, only give 0300 error code

My sons pickup is a 96 Cheyenne 1500 with a 4.3 & Automatic. The problem stared day before yesterday, running very rough & backfiring. At that time it gave 0300 (general engine misfire), 0302 (Cylinder 3 Misfire), 0172 (Right bank rich), 0175 (Left bank rich), & 1441 (Evaporation collection system) codes.
We replaced the gas cap which eliminated the 0172, 0175, & 1441 codes.
The problem still persists with the engine running rough & backfiring through the tailpipe.
The only codes it will give are 0300 and occasionally 0302. I have checked the compression, it is good an all cylinders, average about 160lbs.
I have also cleaned the plugs & checked the wires. All seem to be OK. They have only about 5000 miles on them & are about 6 months old.
I have tried some Gumout Ultimate fuel system cleaner, suspecting some type of contamination, but have seen no change.

Any suggestions?

If the gas is contaminated, what is the best way to flush the system?

The 0302 code means misfire on cyl #2. The last number corresponds with the cylinder. Try switching the plug and or wire to different cylinder to see if it is a plug/wire problem. See if code changes to that cylinder. Is this cpi(spider injection)? You could have random misfire from cpi unit. Also check real good for vacuum leaks.

The 0302 code means misfire on cyl #2. The last number corresponds with the cylinder. Try switching the plug and or wire to different cylinder to see if it is a plug/wire problem. See if code changes to that cylinder. Is this cpi(spider injection)? You could have random misfire from cpi unit. Also check real good for vacuum leaks.
I have done that, & am now only getting the0300. The engine has all new vacume hoses (In the last 3 months) & all of them are tight.
How do I tell if it is a CPI? It is a vortec engine with the plastic upper manifold & aluminum lower. The entire injector system is inside the plastic upper manifold. My Haynes Manual calls it a CSFI...

I suspect a problem with the fuel delivery system. Have you checked to see if fuel pressure holds?

Also how are the start-ups, does the truck crank unusually long before it starts?

You could have a leaky fuel pressure regulator which is flooding out one bank of cylinders.

I suspect a problem with the fuel delivery system. Have you checked to see if fuel pressure holds?Not yet, will have to rent a gage. Where is the best place to check, under the hood or at the filter?

Also how are the start-ups, does the truck crank unusually long before it starts?
No, starts right off.

You could have a leaky fuel pressure regulator which is flooding out one bank of cylinders.How do I check this? Can it be fixed or would the regulator need replaced?

There is a shrader valve on the fuel rail to check fuel pressure. If it doesn't hold, you need to find the leak. Whether its coming out the regulator and leaking into the manifold, or if its a sticking injector.

And the FPR cannot be serviced, its a remove and replace type of part.

There is a shrader valve on the fuel rail to check fuel pressure. If it doesn't hold, you need to find the leak. Whether its coming out the regulator and leaking into the manifold, or if its a sticking injector.

And the FPR cannot be serviced, its a remove and replace type of part.Sorry for slow response. I had to get paid before I could get a fuel pressure gage.
Pressure is 58PSI then bleeds down (engine off check) & sits about 59 or 60 PSI at idle, the pressure fluctuates when idling. I have replaced the FPR, no change.

?

So you just replaced the FPR and no change to fuel pressure?

58psi is a little on the low side. With the engine off, turn the key on to prime the pump. Does the fuel pressure drop off immediatly?

If so you need to find out why the pressure isn't holding whether its a bad one way valve in the pump or if its a sticking injector.

So you just replaced the FPR and no change to fuel pressure?Thanks for the quick reply.
Yes, we replaced the FCR & the fuel pressure still does not hold & did not increase.

58psi is a little on the low side. With the engine off, turn the key on to prime the pump. Does the fuel pressure drop off immediatly?Almost, say 2 to 3 seconds & it starts to decrease noticeably, about 15psi per second.

If so you need to find out why the pressure isn't holding whether its a bad one way valve in the pump or if its a sticking injector.I had not thought of the pump. Would that make the pressure fluctuate when the engine is running? Is there a way to check the one way valve before we drop the fuel tank?

We thought of a sticking injector, & replaced the injector assy with one from another engine that was running when we scrapped the truck it was in. The symptoms have not changed. Either the second injector set had the same problem or the problem is somewhere else.

Is there a good means of checking the individual injectors? My Haynes manual does not give one.

On this motor there is really no easy way of checking the injectors short of specific dealer only tools.

Have you cleaned the MAF sensor? Use specific MAF sensor cleaner and a q-tip. Be carefull not to break the filiments.

On this motor there is really no easy way of checking the injectors short of specific dealer only tools.

Have you cleaned the MAF sensor? Use specific MAF sensor cleaner and a q-tip. Be carefull not to break the filiments.
I told you wrong on the pressure. I re-tightened my test gauge connection today & the pressure results improved somewhat. Engine off pressure is 65psi while the pump is running then drops immediately to 58 when the pump stops. After a few seconds the pressure starts to drop slowly to about 51 or 52 then holds pretty much steady.
Running it goes to 65 while starting then drops to around 58 while running, but still fluctuates a little.
Carefully cleaned the MAF with MAF cleaner & Q-tip, no change.
We even tried a new fuel filter thinking it would improve pressure, no change.

Does this still sound like a pressure problem? :dunno:

If it does, can I check the one-way valve on the pump short of pulling the pump?

If not, any thoughts?

Fuel pressure sounds pretty good to me.

What year is this truck? When was the last tune-up done? If you listed it above, sorry if I missed it. And if it was recent, what brand plugs did you use? Hopefully not bosch.

I know if this is a 95+ truck, and the wires plug onto the sides of the distributor cap instead of the top, the later style distributor caps tend to have issues with cross firing cylinders.

Fuel pressure sounds pretty good to me.OK

What year is this truck? '96

When was the last tune-up done? If you listed it above, sorry if I missed it.[quote] About 3 months ago.
[quote]And if it was recent, what brand plugs did you use? Hopefully not bosch. They were Bosch, P4s. This is the same plug that I have been using for the last 6 or 7 years in my other 4.3's with a cumulative total of about 500,000 miles on 3 vehicles without a problem.
People have told me the Bosch's were problems in the past, so despite my experience to the contrary I tried putting an AC plug (stock recommended for this engine) in the #2, along with a new wire since a 0302 is the only cylinder miss code I have gotten. This has been very intermittent, usually I just get a 0300. Anyway, the problem did not change.
Since the AC's are not expensive I will replace the other 5 just in case, (I have been wrong before) but I am not holding my breath.

I know if this is a 95+ truck, and the wires plug onto the sides of the distributor cap instead of the top, the later style distributor caps tend to have issues with cross firing cylinders.The inside of the cap looks clean, with no spark traces. Can it short out inside the plastic?

The inside of the cap looks clean, with no spark traces. Can it short out inside the plastic?

Yes it can. If its the stock cap, you may just want to replace it just to rule it out.

did you get a chance to replace the cap?? I have a 99 that has to have the cap replaced every 9 to 12 months. Is there a fix to this??

did you get a chance to replace the cap?? I have a 99 that has to have the cap replaced every 9 to 12 months. Is there a fix to this??

What brand CAP's do you use that keep burning out? Try an OEM one. Its a little more expensive, but may last longer. Also, check the plug wires and adjust the spark plug gap .040" for copper core plugs, .060" for platinums. If the wires or plugs are bad causing excessive resistance, the spark will take the path of least resistance. Even if that means burning its own trace through the dist cap and cross firing a different cylinder.

Its funny a company hasn't made an aftermarket dist for the 95-2000 vortec motors that uses the old style cap/rotor, and incorporates the required cam sensor.

that last 2 were Standard brand.

On fuel pressure run a full fuel pressure test.
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.

Yes it can. If its the stock cap, you may just want to replace it just to rule it out.
We did, no fix. Replaced the MAF, same result.

Son is going to take it to the dealer for a diagnosis. The local one will do one for $50, may be money well spent. When he has done so I will let you know the result.

Thanks to everybody for your sugestions.

On fuel pressure run a full fuel pressure test.
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.This problem starts as soon as the truck is started. Runs too bad to drive for 20 miles.

This problem starts as soon as the truck is started. Runs too bad to drive for 20 miles.
Did you check the fuel pressure or see if fuel pump is running?

A fuel pressure gauge will tell you if it has enough pressure to run.

Or you can get a tow truck to take it in for test.
And if good towing insurance they will pay tow to nearest garage.
But may not bring it back to you.


Let us know how it goes.

Did you check the fuel pressure or see if fuel pump is running?

A fuel pressure gauge will tell you if it has enough pressure to run.

Or you can get a tow truck to take it in for test.
And if good towing insurance they will pay tow to nearest garage.
But may not bring it back to you.


Let us know how it goes.Fuel pressure is good, 60+ psi.

He can limp it in to the dealer, <2 miles in town, 30MPH. When he has done so I will let you know what they say it is.

Fuel pressure needs to be 64 -65 lbs on cold start.

Fuel pressure needs to be 64 -65 lbs on cold start.It is, 65PSI cold test.