Running Rich, Will not Start

[t77911s]

1995 RRC SWB (3.9): Truck has been running very rich, can easily smell it, and gas mileage has gone from 14/15mpg to 9/10mpg around town. Truck will sometimes die at idle, choking itself out due to rich, then be very difficult to restart, requiring full throttle to allow more air and drilling starter for a minute or so. At times truck will have to be left where it is to sit for an hour then will restart fine. This has gotten progressively worse now and truck will not start at all. My guess is plugs are completely fouled, so I'll get those replaced tomorrow. My concern is what could be causing this, and this is what I have done so far:

1) Swapped ECU.
2) Checked the Engine Temp Sensor for the ECU at various temps, all ohm reading are right on spec.
3) Checked spark at plugs and coil lead, very strong spark.
3) Swapped out the AFM.
4) Fuel Pressure is around 40PSI when cranking.

I've thought about leaking injectors, but I have had that problem before, and that usually results in very difficult starts after letting truck sit about 15min as the injectors leak fuel in hot engine making hard to start.

Also, Once I get the truck running again, even though the ECU Temp Sensor has good readings, I'll also check the readings back at the ECU to make sure there is not a wiring problem.

I'll also check the O2's as well, may just replace them.

Anything else you guys can think of?

Tim

 

[Blitzracing]

Check the AFM connections, as if they go open circuit it runs very rich in fall back mode. If you have a fault code reader, check its display (its under the passenger seat on some USA spec trucks), or there is the RoverGauge freeware you can download that will give you all the sensor data and fault code info. It needs a cable making up, but the deails are on the Rovergauge web site.

Ive covered some of it here:

http://www.g33.co.uk/fuel_injection.htm

and the RoverGauge software and details here:

http://code.google.com/p/rovergauge/

You cant get the required plugs to interface with the OBD port anymore, but there should be a grounding plug in the port you can use to make up a cable, as the ECU runs OK without it.

It wont be a fault with the Lambda probes- they only trim the mixture, and the ECU will run on the base fuel map without them.

Mark

 

[t77911s]

Thanks, Thats excellent information in those links.

 

[76FJ55]

have you checked the FPR to make sure it doesn't have a bad diaphragm? pull the vac line at the FPR and see if it's wet or smells of fuel. if it does the diaphragm could be leaking fuel into the manifold through the vac line. A better test is to draw a vacuum on the FPR and see if it holds or bleeds down.

 

[t77911s]

Update: Replaced both O2's, and plugs, truck fired right up, let idle for a bit then drove approx 2miles, came to stop sign, car stumbled and died. Very hard to restart, but after working starter off and on for about 5 min, I just pressed gas pedal all the way to floor and spun starter until it finally cranked. Been running fine ever since.

76FJ55: Pulled vacum on PR, it does bleed down, but very very slowly, 20 - 15 in maybe five minutes, as you can barely see the needle move, so it could just be the connections. Fuel Pressure is solid 35PSI.

Blitzracing: Just bought cable to use the software that you posted, just to see what's going on while driving.

Hooked up my LM-1 this weekend, and drove approx 10 miles so far and the AFR's are mid 14's. Sometimes will drop to 14.2 at idle, and go up to low 15's while driving. So at this point, I don't have a rich problem. GOing to leave the LM'1 on for a while, really curious to see the AFR's if it does the stumble and die again. I think the 14's are good.

 

[carlosz]

on the older models, disconnecting the battery will reset the monitors and return ecu to "as built" status thus releasing from limp mode and entering the diveability "re-learn" mode.
normally done to clear adaptations after repairs such as yours.

 

[t77911s]

on the older models, disconnecting the battery will reset the monitors and return ecu to "as built" status thus releasing from limp mode and entering the diveability "re-learn" mode.
normally done to clear adaptations after repairs such as yours.

Thx Carlosz, I Had the battery disconneted for three days before I installed new plugs and O2's, so hopefully that would have cleared out the configurations from when it last ran.

Just got back from lunch, drove the car about 15 miles. AFR's mid 14's.

 

[RoverDude]

Pull the distributor cap. Place plug wire from the coil to cap slightly above center of rotor arm. Turn ignition over. If spark travels to rotor, it is bad. Replace with "quality" unit.

 

[pdxrovermech]

i usually find this issue to be poor spark due to a cheap cap and rotor leaking injectors, or a bad temp sensor.

 

[t77911s]

I have an MSD Dist with MSD Cap/Rotor. I'll check the spark. Temp Sensor ohms out right on spec. Thought about bad injectors.

I'll replace cap and rotor just to be safe.

 

[kferg]

If you pull the injectors you can get your injectors rebuilt from several places. I used Fuel Injection Connection for $16 an injector. They are in AL, took about a week between sending out and getting them back. Witchhunter also does this. Made a heck of a difference. Have you checked the base idle?

 

[t77911s]

If you pull the injectors you can get your injectors rebuilt from several places. I used Fuel Injection Connection for $16 an injector. They are in AL, took about a week between sending out and getting them back. Witchhunter also does this. Made a heck of a difference. Have you checked the base idle?

I've got several sets of injectors, I may just send all the spares off to get them checked. As for the base idle, I've been cheating and using the cable adjustment to set the idle. I'll go thru the correct procedure as soon as I have time. THe truck is running good, but gas mileage is still way way down, 9/10 when it used to get 13/14 around town. Just have not had much time to mess with it.