Narcoleptic 3.0

[beaterranger]

I'm seriously beginning to think my truck is the one falling asleep while driving. Here's the scoop:

91 Ranger Supercab, 3.0L, 2wd, 5spd, 287k

The new: coolant temp switch, coolant temp sender, manifold air temp, charge air temp, IAC, fuel filter, air filter, plugs, coil, h2o pump.

The scene: Driving out of town, slight drizzle, overcast, 9pm, 4lane highway, 35 degrees ambient, very light traffic, cruise set at 70mph, full tank.

The summary: This truck has battled a cold for a while now. Starts up fine but WILL NOT permit driving until it is to full operating temp. Otherwise, as soon as load is applied, it stutters, stalls, and generally pitches a fit like a 3yr old. Allowed the truck to warm up and departed on my journey. Achieved target speed of 70mph, set cruise, and all was well. 15min later, the cruise control shuts off at which point I resume control of the foot feed and work my way back to said target speed. Set cruise again, and the universe is once again in balance. 10 min later, cruise kicks out again. At this point, however, there is zero throttle response. All gauges are normal and no CEL. I immediately depress the clutch to verify that the engine has not stalled and to my shock, the engine is still idling smoothly. Off the clutch and still no response for a few seconds but as I begin to pump the foot feed, the engine slowly begins to respond. I hold the foot feed roughly at what it would normally be at cruising speed and almost as if a valve of some sort slowly swung open, the engine came back to life as if nothing had happened. Again I set the cruise and began timing the occurrences. 9min, 30sec recovery, 7min, 60sec recovery, 4.5min, 60 sec recovery and so on until no recovery at all. Again, all gauges remained normal, spit on the heads to verify that they weren't in fact overheating, monitored the headlights for dimming due to low voltage, etc. Nothing. At all. Everything was functionally normal including the idle. No misses, no misses on prior accelerations, no pinging, no backfiring.

My speculation: Cats clogging and not constricting flow until they have reached a maximum temp (btw, no they were not glowing), MAF flipping out, TPS giving me the , or ECM punching out.

Any thoughts/suggestions? Years of turning wrenches and this has me completely at a loss...

 

[Earl43P]

1st guess would be ignition module, second would be fuel pump relay.

Neither accounts for its cold start behavior however.

 

[beaterranger]

Thanks Earl, those were two possibilities I hadn't even thought of. I will admit that I have very little experience in blue ovals so my question to the 1st guess may be from years of cussing GM's... On Ford products, do the IM's have the tendency to exhibit intermittent failure or are they similar to the GM HEI IM's that just outright fail and leave you with no ignition at all? The fuel pump relay issue I will definitely have to check into also.

The cold start has been sending me up the wall to no avail. Most of my resources inform me that 90% of cold start issues fall on the IAC but since this component has been replaced as well as all temp sensors, I'm lost on what could be causing this erratic condition.

 

[jewalker7842]

EGR valve is another possibly. I had an older truck that threw a fit when it got clogged, but did not exhibit anything like your truck is doing. Like the previous guy said check the fuel pump relay. Other than that I don't knww what to tell you.

 

[beaterranger]

Thanks for the tip jewalker. Unfortunately, this little ranger doesn't have an EGR...it has the port for it, but was not equipped with it for whatever reason. Crazy considering my 86GMC has an egr...

 

[triumphrider-1]

Have you done a compression test on it when it was cold, and warm?

 

[beaterranger]

About a month ago, yes. All cylinders fell within <10% of each other and still surprisingly healthy given the mileage.

 

[beaterranger]

Update: On a hunch, I swapped the TPS out, sprayed a quick shot of cleaner through the MAF and throttle body and cold start performance roared back to life. A quick trip to the interstate and locked in at 70mph, the original condition still seems to remain. 7-10 min down the blacktop and sudden loss of power...30-45 sec to recover. I was able to note this time, however, that there seems to be a high load/high rpm miss. 70mph= ~2700rpm btw. Being the wealth of experience and reputable advice that I've seen posted on this forum, and in following with earl's previous thoughts, I wonder if:

A) Under extended high rpm operation, the ignition control module is warming/deteriorating and thus failing to maintain a consistent spark control which would present the subtle but spotty misfire condition. Or,

B) Under extended high rpm/high load (eg, hills and such), the fuel pump relay is getting hot due to the higher current draw causing a higher resistance in the coil and thus deteriorating the relay's coil and it's ability to maintain contact with the high current poles.

That said, the cruise control failure seems to be residual as this condition has also been tested without the aid of the cruise control circuit with the same results. My thought in regards to (A) is that since almost all ICMs are solid state devices, it would be reasonable to assume that once failed, there would be no recovery. As to (B) it would seem that if the fuel pump circuit opened, there would be no means possible that the fuel system would still be able to maintain idle as presented by depressing the clutch within seconds of the the power loss. My next course of action will be to access a fuel pressure gauge and monitor the condition closely. Otherwise, I'm out of reasonable guesses. Huge thanks to everyone that has offered their ideas, yall certainly have far more understanding of these trucks/engines than I'll ever have so please keep the ideas coming.

 

[triumphrider-1]

I keep circling back to some kind of timing issue in my mind, but not really sure.

When the cruise control kicks out (assuming it happened this most recent test as well) does the accelerator pedal feel like the cable has gone slack?

 

[beaterranger]

Not so far. Each time it happens, I give it a quick bump expecting it to fall to the floor. Good spring back and good resistance when depressed. I thought maybe it was a weak cruise servo but being that the condition is still presenting itself without cruise on, I'm back to guessing.

 

[danger94]

have u takin the ignition moducle offf to get tested?

 

[beaterranger]

Making my way to the shop this morning to do exactly that danger94. Going to pull my wires and ohm them out as well. Is testing the ICM something that AZ has to do or is there a bench test procedure that I can perform at the shop myself?

 

[beaterranger]

My apologies for the delay in updating. I broke a bolt off the thermostat housing (doh!). I began to search for the ICM and, according to the book, it should be attached to the side of the dizzy. However, on my truck, it doesn't appear to be mounted there. Did Ford hide these elsewhere on some 3.0L trucks? Also, am I correct that this model should also be equipped with an ignition pickup in the dist as well?

 

[danger94]

mines a 94 but its on the front core support drivers side near the headlight

 

[beaterranger]

Bingo danger94!!! you nailed it...i've looked all over this truck and never would have thought to look there. Thank you 100x over.