zadigofla

Hello all I am new to this forum. I have a 2001 Chevy S 10 4.3 V6 that just recently started giving me problems coming back home from a 400 mile road trip. After fueling up for the second time I noticed serious sputtering on the highway and I basically had to keep my foot to the floor to stay at 70 mph.

I took my truck to my mechanic friend that evening and he noticed that I had a very consistent misfire in cylinder 4. It was just misfiring the entire time we were talking. He pulled the plug out and noticed that it was black and smelled rich. He suggested that it might be the fuel pressure regulator causing my bad mpg, loss of power, sputtering, and the misfire on cylinder 4 as he believed that the leaking fuel was entering that cylinder from the hole in the plenum.

Fast forward a week to tonight and I attached a fuel pressure gauge to the service valve and discovered that I’m not losing fuel pressure. The pressure goes up to 60 psi and then stays at 45 but doesn’t go down below 40. I think that means my fuel pressure regulator is fine, as are my injectors (not leaking gas). The weird thing is that while the truck is running with the gauge on, the needle is erratic, going between 45 and 58 very rapidly. While accelerating the pressure never exceeds 60psi. Is this a bad fuel pump of filter?

I texted all this information to my mechanic and he now thinks it might be a stuck or bent valve (4th cylinder) or a bad intake manifold leak. What do you guys think? I did get code p0304 and a service engine light while on that road trip.

Thanks

oilcanhenry

The P0304 means that it is indeed your number 4 cylinder that is the issue. Here are some of the things that might be the issue(s):

Faulty spark plug or wire
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector
Burned exhaust valve
Faulty catalytic converter(s)
Poor compression
Defective computer (ECM)

I'd' run a compression test of that cylinder, or all of them, first myself, That way you'll know if you have a bad valve or bad/stuck rings, as your compression will be low or not within 15 PSI of each other, as they should be..

The problem with the OBD II P0300 issues is that can indeed be many things as you can see. If it's a fuel injector you might run a can of Seafoam or Techron Complete down the gas tank, to clean the injectors up, although they can malfunction too.

zadigofla

Well the truck is at my mechanic’s house now. He’s going to do a compression test on all the cylinders and try to get to the bottom of the issue. He thinks it could be multiple things.

I bought the truck from a guy who had it non-op since 2016.

When I came back from my road trip and my mechanic checked the truck he could get a ground on the frame so he believes it’s even missing that! Weirdly when the sputtering started on the highway after fueling up the radio’s clock reset. The entire time it was sputtering we’d adjust the time and a few seconds later it would reset. Also, when I drove the truck to my mechanic’s house the stereo was completely dead.

oilcanhenry

Non-operational is not good for vehicles. Seals start leaking/hardening, things start rusting or getting corrosion.My advice to anyone reading this is to just sell the vehicle if you are not going to operate it, For instance I run my heater with the recycle on during hot summer months (with the windows down of course) as it seems to keep issues at bay if one does so. One of the hardest things to work on in a vehicle is under the dash stuff, which means your heater core and your air-conditioning evaporator.

With the A/C, it will come on if you use the defroster, but although I am told that some heater cores run coolant all the time, I'm not taking that chance, so I run it hot as hell every few weeks. I HATE working on the under-dash or on the climate control box, so if running it hot keeps the coolant from damaging the core, that is what I do.

Same with the A/C, but seals tend to get dry if not in use so it best just to sell it, if you don't use it much or at all, IMO. Personally I don't like the idea of a heater core running in summer all the time as it just makes the A/C work harder. Neither one of my Chevrolet's are designed like that at all thankfully. FUBAR used to use full time heaters, back in the day and no one liked those at all.

zadigofla

Here is a video of the fuel pressure test I did about a week ago. The truck is currently at my mechanic's house, awaiting a cylinder compression test.

hanky

What about this,
The up and down reading on fuel pressure, what can cause that and also load a cyl so bad to misfire ?
Very likely a sticking fuel injector. cyl 4
To confirm this switch injector with another cyl and if the misfire moves , you have your answer.

oilcanhenry

Likely a fuel pressure regulator, going bad. Once you get off idle it seems to become steady, works correctly. After all its 20 years old.

zadigofla

My mechanic found the reason for the 4th cylinder misfire: a damaged distributor bearing.


Black marks on rotor circled is where it's hitting the inside of the cap.


He said the rotor was wobbly and hitting the #5 and #6 terminals, sending the spark scattering to into #4. He's thinking of cutting a relief in the rotor so it'll stop hitting to see if the misfire goes away -- to test the conclusion. Going to replace it with a new Delphi distributor.

He also tested the compression on the cylinders and said they were excellent, 165-180psi.

Next he's going to test the fuel pressure (again) and vacuum lines for leaks.

Keep you guys updated.

zadigofla

My mind is blown guys. Literally the thing causing the issue was the wobbly distributor. Here is a video of my mechanic testing the fuel pressure and vacuum: . The fuel held pressure after the truck was off and the vacuum steadied. The alternator isn't making good sounds and its bearing isn't happy, but it's reading at 14.3V. Looking at the data he's noticed that the rear o2 sensor is reading low voltage, said it might be a sign that the catalytic converter is on its way out. Overall, the truck sounds good but there might be a tiny vacuum leak.

oilcanhenry

Might be able to determine that with a vacuum gauge (seems like no one uses those anymore), unless that's the gauge the mechanic used. Yeah, the distributor bearing going out is something I've never seen before, but sure, it could do this. You learn something new every day in life. Might have a small intake manifold leak. I've seen people actually spray gasoline on the manifold to test for leaks, but something less flammable, like WD-40 would work as well, IME.

I've heard of people using different substances to clean a catalytic converter out, like Methanol or Acetone (don't use without gloves and a filtered face mask as these can go right into your body though the skin), but I've never seen it done for myself, so who knows?.