Hatsuwr

Hey everyone, in the middle of a cross country road trip with the family and am experiencing a bit of a problem. If I push too hard on the gas, the engine will start to lose power, to the point of dying completely if I am going slow or in neutral.

The problem seems to get much worse as my fuel level gets lower as outside air temperature are higher, and it also seems to get worse the longer I have been driving continuously. It is somewhat sporadic though. I've gotten down too nearly empty with no issues before, but I've also had issues with nearly a full tank. Those just seem to be the general trends.

If it loses power like that though, shifting to neutral, shutting of the engine, and restarting will usually get me at least a few more miles.

My best guess is that the fuel pump is slowly dying. Any other thoughts though? The sporadic nature of the issue seems unlike a fuel pump failure to me. I have a limited tool set with me, and only a few more commonly broken parts.

No codes. It had P0505 for a few minutes when it was really bad, but that quickly went away on its own. Around that time there was a sort of muffled popping sound that I'd guess was unburned fuel igniting in the exhaust.

Thanks for any advice!

dave1123

You should know by now we need to know what year, model, and engine we're talking about. Otherwise I, for one, can't even begin to diagnose your problem! Like is your jeep new enough to have the drive-by-wire throttle?

Hatsuwr

Ah, sorry, 96 ZJ Laredo with the I6

dave1123

Okay, a P0505 is an idle air control motor malfunction code. I was thinking throttle position sensor. I'm still suspecting a TPS malfunction. I ruined one by spraying Seafoam directly into the throttle body while it was running. It ran down the shaft thru the seal into the sensor itself. This resulted in very rough idle and total chaos above 1500 rpm, plus no power if put into gear and trying to drive.


If you're on the road, it's something quick and dirty to try replacing.

97grand4.0

What Dave said. to rule out fuel it would be nice to just hook a fuel pressure gauge up and see the fp.

Hatsuwr

As far as the IAC, I had issues with mine about a year ago. Nothing really like this though, and the IAC I have now is fairly new.
I don't think it is the TPS, since the throttle position where I have issues varies. I brought a multimeter though, so I will test both.

I think I may have thrown in a fuel gauge... If not, I might just have to pick one up on the road.

Hatsuwr

Well, made it to California finally, and have a few days to work on it.

I think I was wrong before about the issue being worse with lower fuel levels. It seems as if it is actually related to the outside air temperature - 90+ degrees and the issues get pretty bad. 80's aren't a big deal, and very little happens below 80.
I think that the time spent sitting while refueling was enough to cool something, and so it seemed as if it was fuel level related.

I popped the hood as I was driving so it was just sitting on the latch to get some more airflow in the engine bay to test out my new theory in regard to components in that region. It did seem to help a bit, but nothing so significant that I could make any sure statements.

Turning the engine off and on - even while cruising at freeway speeds - still helps get a bit further.

Tested the IAC and TPS - they seem fine. Waiting for an adapter for fuel pressure. Opened the port on the fuel rail though, and it seemed like pressure was fairly high even when the problem was about at its worse. Don't have anything less subjective for now though.

The fuel filter and pump were replaced late last year, and the fuel tank was very thoroughly cleaned, otherwise I might suspect either the inline filter or the screen on the pump were being clogged somehow. Doesn't do much to explain the apparent temperature relation though.

97grand4.0

Starting to sound like Bill and Ted's Great Adventure.
Did you ever look into the cam and crank sensor? Crank sensor usually wont start, but the cam sensor is temp sensitive and causes a variety of symptoms..a Scan Tool with graphing is a must have tool also. That and FP tester. You need some data to stop shooting in the dark.

Hatsuwr

Have a scan tool, recorded a few drives while experiencing the issue. This is my first time using that aspect of it though. Any ideas on what I should be looking for? It recorded:
Time
O2 voltage (Bank 1 Sensor 2)
Short term fuel trim (Bank 1 Sensor 2)
Vehicle speed
Calculated load value
Engine coolant temperature
Short term fuel % trim - Bank 1
Long term fuel % trim - Bank 1
Intake manifold absolute pressure
Engine RPM
Ignition timing advance for #1 cylinder
Intake air temperature
Absolute throttle position
O2 voltage (Bank 1 Sensor 1)
Short term fuel trim (Bank 1 Sensor 1)
Input voltage read by the scan tool

Hatsuwr

Here's a csv of a drive. Not a whole lot to see. As throttle position increases past a certain point, acceleration slows or drops, RPMs drop, the fuel trims go extremely high, and one of the O2 sensor voltages drops quite a bit. That happens a few times on this drive.

I also noticed quite a bit more of what sounded like fuel igniting int he exhaust manifold (though I wouldn't say that's what it is for sure) since I was intentionally prolonging the issue.

97grand4.0

They were the best of times, they were the worst of times. How'd we make out on the fuel pressure tester? Any luck finding one of those? Oh you have a scan tool? How about codes, does it show any codes?

97grand4.0

Converter plugged.

dave1123

Good catch!!

97grand4.0

Thank you.

Hatsuwr

No codes, except for a P0505 and too lean mixture that came up briefly when it was the worst of times. Pretty sure those are just signs of the already clear symptoms, rather than of the problem.

Waiting for an adapter for the fuel rail.

Cat is pretty new, plus, would it being clogged explain the temperature correlation, or the temporary alleviation of the problem when restarting the engine?