Engine/Transmission (1994 - 1998) Help! Runaway Engine!

[strick]

My '98 12v 5 speed had a runaway situation a few hours ago. I'll set the stage and ask for your help. I get in and crank the truck up and notice that all the guages are dead and the odometer is blinking on and off. I wonder what in the heck is going on, but I figure I'll deal with it when I get home. Big mistake. Put the truck in reverse and give it a hint of throttle and the thing goes WFO. I cut the key ASAP and the truck dies. Whoo! Try it 3 more times. Same thing! The pedal is not sticking. As soon as I touch the trottle it goes WOT. I first thought it might be the gov springs, but rule that out since the guages are dead too. I unplug the PCM plugs just in case there is corrosion or something. A buddy recommends unpluging the cruise control since that is the only computer controlled part of the injection pump. Truck appears to be fine,so I drove it home. The guages are still out. I'm fixing to check and see if alternator is charging. I doubt it. What in the heck happened and what do I need to check out? Am I looking at a dead PCM? Help me out guys. Thankfully I have my '99 to drive while I figure this thing out. I must admit I liked to have pooped in my pants. I couldn't imagine what would have happened with an engine running away w/ 4k gov springs in it. Well never mind. I know what would have happened. Big boat anchor. Any help would be appreciated. Thanks, Jason

 

[Heepdriver]

With the computer unplugged the alternator is not charging. the only thing that do this is the cruse control. Leave it unplugged ( are ours vacuem actuated? you could disconnect and block off vacuem source) and reconnect your pcm. ck your throttle spring by the tps and your throtle linkage for worn ball sockets and being connected.



good luck

 

[Jeff H]

Maybe the over valved forum would do ya?

 

[Bill Lins]

ck your throttle spring by the tps and your throtle linkage for worn ball sockets and being connected.

No TPS on a 12 valve w/5 speed.

 

[Heepdriver]

99, whoops didn't even look at his year, and yep no tps.

 

[strick]

My question is this. With the PCM plugged in I still don't have any guages whatsoever. The odometer is also blinking on and off. Is there some kind of reset? Is there anything to diagnose on the PCM or should I just get a replacement? Thanks for the help guys, Jason

 

[R.ebel]

Sounds like you might have a loose ground wire. Check all your connections.

 

[Howard Durand]

I believe the cruise control electronics is part of the PCM and, if so, you may have to replace it.

Have you tried disconnecting the controls in the steering column?

 

[strick]

I've got the cruise control cable disconnected from the injector pump to prevent this problem again, but I still don't have any guage readings with the PCM plugged in. The only thing I have is the odometer blinking. I guess I'll just throw a PCM at it and see if that returns guage functions. What specifications do I need for the PCM replacement? Obviously 12v, 5 speed. Are they year model compatible?

 

[Howard Durand]

If you have a dealer you can trust, have them run a diagnostic on the PCM before shelling out a bunch of money for a new one.

 

[MKinner]

Did you unplug the PCM with the batteries hooked up? If you did, the PCM will be fried... .

 

[outdoors]

Like R. ebel said...



If you know of a "decent" local dealer,

they usually know right where the problem ground connection is.

Someone here I'm sure has had this happen before.

You might try searching some "keywords" here.....



Being out two hours labor is always cheaper then a PCM.

And if they find the PCM as the problem, then problem solved too...

and you are back on the road.



Please let us know what you find out too. Good luck.