4.0 with 2 issues - same root cause?

[Flingarrows]

I have a 99 Ranger 2wd 4.0 automatic with 100k on the odometer. I had constant codes for lean, misfire, etc. I clear that with a new set of heads last fall, as well as upper and lower intake gaskets, tpfe and hoses (tpfe cracked), Coil, plugs wires. Incidentally, the old coil was not bad, so I have a spare. The burning oil smell was gone, idled smooth, no codes.

Fast forward to the last few month. Wife tells me that truck stalled, and wont go. Kind of ambiguous, but it is happening more often and I finally experienced it. So this is an intermittent thing. when it runs good, it runs good...

Symptom#1 pull up to a stop, idle drops very low, and stalls. feathering pedal keeps it running. I have has 2 incidents now, where is dies and starts hard and wont rev up, then goes away after a little while.

Symptom#2 and cruising speed, it intermittently feels like a cylinder is not firing. This goes in pulses of maybe 5 seconds of rough, then smooth for 5. This cycles like this for the whole drive. Other times it runs fine.

No CEL, but bought a code reader and had a code relating to TPS and MAF not syncing.

It had the dying thing today, and I drove it hard to keep it going, and then it went away. No stored codes...

Took it for a drive after work, and only had the missing thing at highway speed. Again, no stored codes.

Here is what is new in the last 3-4 weeks:

MAF, TPS, IAC, Battery (interior light left on, was time for a new one anyway).

Any ideas?

 

[Flingarrows]

Any chance that the fuel pump is going out, or is that a go/no go type of thing?

 

[RonD]

'99 has a returnless fuel system, it should have a fuel pressure, at the rail, of about 60psi.

I would rent a pressure tester or find some way to test the pressure.
test it at idle and then at a steady 2,000rpm, for a minute or two.
Then shut down engine and make sure pressure holds.

In the fuel tank there is a check valve that maintains the pressure, the computer has no way to tell the pressure, it just assumes 60psi.
If the check valve is leaking pressure, then pressure could drop while driving, giving you a lean code, or a stall out.

The computer runs the fuel pump for 2 seconds when key is first turned on, then it runs it on and off based on engine RPM and speed, and also throttle position which could explain why "feathering the gas pedal" can keep it running.
A fuel line leak could cause the above as well, but you didn't mention the smell of fuel.

Also remove the gas cap or loosen it, if the tank is not venting properly you can build up a negative pressure in the tank so fuel pressure would drop as fuel pump could not pump as much fuel as it should.

There is also a Fuel pump relay, that is how the computer turns fuel pump on and off.
These are known to fail, but usually cause a no start, not an intermittent issue, but there is always a first time.

 

[Flingarrows]

Thanks Ron, I'll get a tester for the fuel pressure as my next step.

Also, no raw gas smell

 

[Flingarrows]

Fuel pressure is good, but truck wouldn't act up. Changed the pump. A week later acted up for most of a 300 milevtrip, and threw a code indicating tps and maf not reading correctly. Those parts had been changed already.

My buddy has some so of real time PCM monitor. He drove it for 2 days before it happened again. He said that the fuel trim numbers when crazy, and indicated some sort of a ground fault. He tore the harness open, cleaned all of the grounds, added an additional ground. No reoccurrences so far... I'd did throw a p0174 code today for a lean bank, but ran fine. I'll have to trace down what might be a vacuumed leak


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[Flingarrows]

update:
No reoccurances since adding the grounds. The lean bank 1 and 2 turned out to be the carter replacement pump putting out low pressure. Ordered a motorcraft replacement.

It's good to have a reliable truck back

 

[RonD]

Good work
Thanks for the update

Was the added ground at the PCM or in the engine compartment?

 

[Flingarrows]

On new ground was added from the battery to the body, and on from the body to the engine

 

[bmerr98]

If you're still looking for a vacuum leak throwing a lean code check your egr valve. The diaphragm can give out. Had mine plugged off for a couple years before I replaced it. CEL stayed on most of the time but it ran ok.

 

[Flingarrows]

If you're still looking for a vacuum leak throwing a lean code check your egr valve. The diaphragm can give out. Had mine plugged off for a couple years before I replaced it. CEL stayed on most of the time but it ran ok.

Good info, thanks