After a long time, im back.

I did got a Scanner, got a great deal out of a Solus Pro and pulled the trigger on it.

For several weeks I kept data logging with it and was able to reproduce the issue several times, however nothing on the readings would look odd. Values on TPS, MAP, Engine RPM, fuel trims, O2 values everything looked just normal, nothing out of the ordinary. I do feel some misfires but for some reason the scanner is not picking them up, the counters always show at 0 on all cylinders

Over the last months I have kept happily throwing parts at it, so far

1. Changed the O2 sensor --> no changes at all, issue still there
2. Took the cat converter off and welded a straight pipe instead --> I feel a bit more power, however the issue is still there, I think is doing it less often than before tough. As I mentioned it only happens under load and I feel that when removing the cat there seems to be more power, then the engine is not as loaded as before…..

This weekend I did a compression test and leak down tests, here is what I got
Compression

1-->160 2->170
3->175 4->160
5->160 6->165
7->165 8->160



Leak Down
1->22% 2->23%
3->15% 4->22%
5->25% 6->22%
7->23% 8->20%

Also installed a mechanical oil pressure gauge and got the following
Idle Cold -> 60 PSI (just after turning it on)
Idle Hot -> 34 PSI
3000 RPM Hot -> 62 PSI

So, in summary compression tests look within specs, even considering that my engine is 200,000 miles! Leak down looks good as well, this means that both piston rings are relatively ok and valves are closing/sealing properly.

The scanner tests seem to indicate the there is no sensor providing wrong readings that would make the PCM to command something that would cause the issue..

So far, the only things that I can think (and I haven’t changed so far) are

1. Fuel pump
2. Muffler (I mean, if I took off the cat converter I could also knock the muffler off, maybe it is clogged?)
3. Something I have started to think is, maybe the valve springs? Perhaps they are getting weak and not closing the valves fully in time when going at highway speed?

 

Compression/Leakdown numbers look good. A seafoam treatment may not hurt though.

Not picking up any misfires is somewhat disconcerting..... How does your trans fluid look? Last time it was changed?

Seems to me, if it's a misfire YOU can feel, the PCM should most certainly pick up on it.... But, my V-10 had a DEAD miss, (burnt thru plug wire, that cylinder simply was not firing at all.) and the PCM never caught on....... That one REALLY puzzles me....... Don't suppose you have another PCM you can toss in there, and test that way, do ya?

 

Remember the pushrod engines don't have knock sensors. The PCM checks the rich/lean O2S pulse against the fuel sync to determine when a cylinder is lean, to set a misfire code.

 

O2 sensors. They control your fuel trim

 

already changed o2 sensor

Im replacing the fuel pump this weekend. I have been doing several days of engine misfire checking with the solus pro and have noticed that i do have random misfires now and then when going above 75 mph.

Even that i tested fuel pressure sometime ago and it checked good this still looks a lot like a fuel delivery problem so im changing the pump and see if it helps

 

Stay away from air tex pumps, delphi, or denso please. Yes, they are more expensive.

Before you spend the money, unplug your O2 sensors, (at least any front sensors, before the cat, not sure how many you actually have there.) and drive it for a while. Problem gone?

 

HeyYou, I am troubleshooting the exact issue with a 98 Dakota (5.2). Earlier in the thread, you mentioned something about disabling OD as a part of the testing. If the issue does not persist when OD is disabled, is there a common cause for the issue? As with energumeno, I have thrown plenty of parts at the issue, but still experience the problem...just not while in OD.

 

If the problem is dramatically reduced when you turn O/D off, that implies its an engine miss, and you need to diagnose WHY it is missing. If you haven't done a tune up for a while, that is a good place to start.

 

Should have read this before...

I already changed the fuel pump, actually i had a Delphi in (installed it like 4 years ago when the oem fuel level sending unit stoped working), this time i got a Bosch. I tilted the bed this time to be able to run a voltage drop test while at it, everything checked ok

I havent tested it much yet, but im still registering high speed multiple misfires on the solus pro, mostly when im driving above 75 so most likely the issue is still there.

Next step --> disconnecting the o2 sensor and see if anything changes?

 

Wow, that's in nice shape, and I love the color.

Yeah, unplug the O2, and see if anything changes.