The issues keep piling up - '91 2.9 runs rich, shuts off, codes 41 & 42...

[RonD]

Computer monitors Fuel pump voltage.
When computer grounds the Fuel Pump Relay, 12volts is sent to inertia switch and to the computer.
Computer will turn on CEL if that voltage goes away while it is Grounding the fuel pump relay.
CEL will go off when 12volts is back.
Could be Fuel Pump Relay or fuel pump power wire to fuel pump relay, wires get corroded under the relay socket

Computer doesn't really have any way to monitor spark system, TFI on 2.9l, it would turn on the CEL if pulses from TFI module were stopped, and probably turn off fuel injectors, not sure on that though.
Restart probably wouldn't be possible, and CEL would stay on not go off, if it did restart.

Fuel and spark are the only two things I can think of that will cause engine to die as described

 

[Fairlaniac]

So I get home from work and quickly do a scan for curiosity sake. On KOEO after the three light flash signifying a 6 cyl and the one separator flash the scanner starts flashing, the engine is stalling and back to running, I hear solenoids clicking all over the place it seemed and finally stalls. So I hook up my fuel pressure gauge as I want to see if I lose fuel pressure during the test. This time the needle is fluttering between 75-95 psi. Once the KOEO checks start the engine revs changed and the needle stabilized around 70 psi and then the flashing and clicking started again. However the pressure didn't drop. It keeps firing up and shutting off. When off the fuel pressure slowly decreases. It reminds me of the Batmobile with all of the light flashing . So is it wise to proceed and check the fuel relay , connection and wiring? I won't have time tonight, possibly tomorrow.

thanks,

 

[RonD]

1991 ranger should have 30-40psi at the fuel rail.
Not sure the '91 fuel pump can generate 70psi, but if it can then Fuel pressure regulator(FPR) on the fuel rail is bad.
It is no longer opening when engine starts, engine vacuum pulls it open.
One of the tests of the fuel system is to pull the FPRs vacuum hose while engine is idling, pressure should go up to 40-45psi, then reconnect it and pressure should drop to 30-35psi.
Never seen above 50psi on a fuel system with return fuel line

High fuel pressure would give you Rich codes same as low pressure gives Lean codes, and bad FPR could cause both, depending on its mood.

But there is no CEL for FPR so at a loss of why it came on outside of engine stalling, CEL is on when engine is not running but key is on.

 

[Fairlaniac]

RonD, I appreciate your time and efforts with my questions. I'll check the FPR tonight and see how it responds when the vacuum line is pulled.

Thanks!

 

[Fairlaniac]

So I hook up the fuel pressure test gauge. Upon a little idle time the engine shut off again. Did this a few times until warm. Finally while running and the pressure fluttering between 75-95 psi I pulled the vacuum line and here is where I may have found my issue. It's probably safe to say my fuel pressure regulator is faulty when fuel flows out the vacuum line? Looks like I'll purchase a regulator. Stay tuned for the conclusion. We'll see if this cures all.

Thanks RonD.

 

[RonD]

Yeh......thats not suppose to happen

That fuel would be sucked into intake and give you the Rich codes

 

[Fairlaniac]

I replaced the fuel pressure regulator yesterday. I was hoping to post a success story, well it is somewhat. Between yesterday and today I put about 150 miles on the Ranger in two trips. So the engine had at least two one hour plus runs, some idle time and local driving time. I was feeling good, no issues, the idle is smooth around 885 (per timing gun tach). No check engine lights. I'm thinking success. Just when I said to myself, "I think I nailed it" I pull in the driveway. Just as I was about to turn it off the idle dropped and surged, dropped and surged, etc... As it was doing this the check engine light briefly flashed. I was doing it for 10 minutes as I just sat there letting it do it's thing trying to figure it out. So I shut 'er down and get my fuel pressure test gauge and hook it up. Smooth pressure about 35 psi. Pulled the vacuum line and it went to 40-ish psi. Didn't see any issues there but again it started to drop & surge. So I hook up the code reader and elevens across the board. No issues. However it still is drop & surging. I was trying to pin point any noises. I heard a possible click like a solenoid when it would drop on RPM. When it drops it almost shuts off. When it does this the fuel pressure goes to 40-ish. I figure the engine is losing vacuum to cause this. Just as if I pulled the vacuum line from the pressure regulator.

I'm not sure what to check next, any ideas?

Thanks,

 

[RonD]

Unplug EGR valve's vacuum hose, this should not be used at idle at all so there should be no vacuum present on the hose.
If EGR valve opens at idle engine can stall out, and you said you may have heard a solenoid click.

Computer operates EGR system using a solenoid, it pulses 12volts to the solenoid causing it to pass a little or alot of vacuum to EGR valve, opening it a little or alot.


IAC valve, see if the computer is using the IAC valve to cause the surging.
After engine is warmed up unplug IAC valve, idle should drop down to 500 or engine may stall, if so use your hand to manually hold open throttle plate enough to keep idle at 500-600.
If you still get the surging then it isn't the computer or IAC valve doing it.

Spark timing, if you have a timing light check if spark timing is changing causing the surging, TFI systems can have odd issues

 

[Fairlaniac]

I'll check that. One other thing I tried. As it was surging and dropping I held the throttle at 2500 rpm. While holding it there and it hit one of it's drops the rpm stopped at 1000 or so even though I did not move the pedal, then it would surge up and down again so it's not just an at idle situation.

Thanks,

 

[RonD]

Then I would pull off the vacuum hose on EGR valve and plug the hose, then drive it that way.
You should get a code eventually if EGR system is being monitored properly, but if it is the source of the stumbling that should go away.

EGR system is there to lower combustion temperatures mostly when engine is under load(accelerating or going uphill), this lowers NOx emissions which spike at higher temps, but as a side benefit it also prevents or reduces pinging/knocking from pre-detonation that occurs when cylinder temps get higher.
So if you start to get pinging back off throttle a bit, pinging is very bad for engine.

 

[Fairlaniac]

I thought '91's 2.9's have no EGR? I don't see any?