SOLVED! I6 severe miss

Jkesselr

Member
Hey guys, I am working on a 2002 TB 4.2 I6. The wife hates to fill up, so she is constantly running it low on fuel. I have preached about the fuel pump forever, but it falls on deaf ears. The truck drove perfect, but was low on fuel. I stopped to fill up and when I went to start it, it died immediately. I restarted it and it was missing like crazy. SES started blinking. I could put it in neutral and rev it, but it took probably 5 seconds with it floored in neutral to get it into the upper RPM range.

I limped it to the parts store to pull codes. It only pulled a P0300. I bought a coil and a set of Delco plugs. I disconnected each coil one at a time, with no worsening of the miss. It took having 3 coils unplugged before the idle worsened more. I started adding back coils with each improving idle quality slightly. I rolled a set of plugs in it and all were clean and dry after having approximately 60k on them. Next, I put the new coil in number 1, no change, so I moved it to number 2, no change. I kept doing it through all of the cylinders with no luck.

I am not certain it is a spark issue now. Any chance the P0300 can be caused by a fuel problem? I put a gauge on it. Key on, engine off, it read 53 psi on the prime cycle, but dropped and held at 46 psi once the prime cycle stopped. Whenever I start the truck the needle on the gauge is a blur between about 50 psi and 56 psi. It literally moves so fast it is a blur. When the engine sputters more the needle is at the lower end of that range, but I don’t know if the idle suffers because the fuel pressure drops or if the fuel pressure drops because the idle suffers. Kind of a chicken and egg issue. Given this info, what is the chance that it isn’t a fuel pump? What about a filter? Fuel pressure regulator?

I am at a loss on this one. Any advice or ideas on how or what else I can check? Please help me!!!

John
 
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TequilaWarrior

Well-Known Member
Hey guys, I am working on a 2002 TB 4.2 I6. The wife hates to fill up, so she is constantly running it low on fuel. I have preached about the fuel pump forever, but it falls on deaf ears. The truck drove perfect, but was low on fuel. I stopped to fill up and when I went to start it, it died immediately. I restarted it and it was missing like crazy. SES started blinking. I could put it in neutral and rev it, but it took probably 5 seconds with it floored in neutral to get it into the upper RPM range.

I limped it to the parts store to pull codes. It only pulled a P0300. I bought a coil and a set of Delco plugs. I disconnected each coil one at a time, with no worsening of the miss. It took having 3 coils unplugged before the idle worsened more. I started adding back coils with each improving idle quality slightly. I rolled a set of plugs in it and all were clean and dry after having approximately 60k on them. Next, I put the new coil in number 1, no change, so I moved it to number 2, no change. I kept doing it through all of the cylinders with no luck.

I am not certain it is a spark issue now. Any chance the P0300 can be caused by a fuel problem? I put a gauge on it. Key on, engine off, it read 53 psi on the prime cycle, but dropped and held at 46 psi once the prime cycle stopped. Whenever I start the truck the needle on the gauge is a blur between about 50 psi and 56 psi. It literally moves so fast it is a blur. When the engine sputters more the needle is at the lower end of that range, but I don’t know if the idle suffers because the fuel pressure drops or if the fuel pressure drops because the idle suffers. Kind of a chicken and egg issue. Given this info, what is the chance that it isn’t a fuel pump? What about a filter? Fuel pressure regulator?

I am at a loss on this one. Any advice or ideas on how or what else I can check? Please help me!!!

John
The needle being at the bottom of the range may be happenstantial, however it is an electric fuel pump. Unless the amp draw is increased for some reason, I would think the fuel pressure loss is a cause of the flutter, not the other way around. I agree with @xavierny25 - a new fuel filter is in order.
It's easy to change on an 02.
Pull the fuel pump relay. Crank the engine - if it starts let it run until it dies. Fuel pressure should be at zero afterwards. You want to depressurize the fuel line before pulling the lines off the filter. Once the pressure is relieved, pull the lines - remembering where they go, I can't remember if it's possible to mix them up. The holder the filter goes in to sometimes breaks when removing the filter, many people just zip tie the new one in to place. Replace fuel lines. Turn engine to ON and let the priming cycle complete - I usually do this a couple times before starting. That should be it.
 
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Jkesselr

Member
So you guys think this could be as simple as the fuel filter, or you think it isn’t just a step in the diagnosis I need to try first?
 

xavierny25

Well-Known Member
So you guys think this could be as simple as the fuel filter, or you think it isn’t just a step in the diagnosis I need to try first?
It's a worth while step in the diagnosis since your wife likes to drive around with an almost empty tank, doing that enough times the filter will get clogged up with junk from the very bottom of the tank.

Honestly it might even be the solution to your issue as a whole.
 
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Jkesselr

Member
I replaced the filter tonight and the fluttering fuel pressure needle is gone, and fuel pressure is a steady 54psi. Unfortunately, the truck is still missing. It is still throwing only a P0300 code. Spark advance fluctuates at idle between roughly 4* and 28* at idle. TPS shows about 10% at idle and only goes up to about 30% even at WOT. B1S1 shows about 2% and B1S2 shows about 99%. I am at a loss as to what to try next. Ideas?
 

Beacon

Silver Supporter
I'm still new to this platform, but (and correct me if i'm wrong) you're saying you timing is not consistent, so I'm pretty sure, the start of timing is the crankshaft position sensor. other things to check for, good ground, and loose wires/connections going to the coils. Although it does seem like there are multiple problems going on.
 

TequilaWarrior

Well-Known Member
I replaced the filter tonight and the fluttering fuel pressure needle is gone, and fuel pressure is a steady 54psi. Unfortunately, the truck is still missing. It is still throwing only a P0300 code. Spark advance fluctuates at idle between roughly 4* and 28* at idle. TPS shows about 10% at idle and only goes up to about 30% even at WOT. B1S1 shows about 2% and B1S2 shows about 99%. I am at a loss as to what to try next. Ideas?
I'd start checking coils/plugs all over again. Unplug a coil at a time and look for worsening or improvement when you plug it back in. Your bad fuel filter may have been complicating an underling coil/plug problem.
 

TJBaker57

Well-Known Member
Just going to throw this out here....this all started immediately after filling up. Is it at all possible you got some bad gas? Some water maybe? Used to happen back in the old days, don't hear of it much anymore though with current regulations having eliminated so many bad and leaking underground tanks.
 
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Jkesselr

Member
I will look into the crank position sensor and recheck all of the new coils. As for bad gas, I do not think this is the issue, as it started immediately after I filled up - like whenever I first started the truck. In my experience, when you get bad gas, it takes a couple minutes for the bad fuel to make it’s way from the tank to the engine. It isn’t instantaneous. I suppose anything is possible, I just don’t see I think as being probable. Is there’s a simple check for a crank position sensor or cam position sensor on these trucks?
 

Mooseman

Moderator
TPS shows about 10% at idle and only goes up to about 30% even at WOT.
It is normal for the PCM to limit throttle when in P or N. This is to prevent over-revving the engine beyond 4000 RPM. And even if driving, it will slowly go to 100% at WOT due to torque management.

There is no check for the sensors as such. When they go bad, they throw a code. You could try cleaning the cam sensor. Don't touch the crank sensor or you may wind up needing a CASE relearn.

Might be worth it to do a compression test just to rule that out.
 

gmcman

Well-Known Member
Did you by chance fill it with diesel or E85?

Probably not likely but I've seen and heard of this quite a few times.

Be careful checking, shield eyes, but dribble some fuel from the test port by the filter and see if it's oily.

If the tank was empty it probably wouldn't even start. Just something to check.
 
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Jkesselr

Member
I don't know how to describe it, but it is like the engine is bound up in terms of trying to rev it. In the past, I could whack the throttle and it would rev as you'd expect. Now, it just doesn't gain RPM like it should. What I keep going back to, that is leading me more toward electrical is the sudden onset of it. It literally ran perfect when I pulled up to the pump, shut it off, and when I started it back up, it immediately died and then ran like hell when I restarted it.

I will look into codes for CPS and whatnot. Definitely didn't get diesel or E85. I have been bathed in gas the last two nights, so we are good there.
 
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Jkesselr

Member
Solved! I never could get a code narrowing I think down further. On a hunch, I rolled a full set of coils in it and it is perfect now. I’m sure I didn’t need a full set of coils, but I wasn’t honestly to the point of just tossing parts at it. It ended up being the first real parts I threw at it and it worked perfectly. I have no idea why it didn’t give me a code by particular cylinder, but when I got to thinking about it, I bought it with a severe miss 5 years ago and it ended up being a coil then and it didn’t give me anything more than P0300 back then either. I guessed on a particular coil being dead back then based on condensation on the boot. It fixed it then and it fixed it this time too. I hope this follow up helps someone in the future. Thanks for all of the help guys!
 

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