So after driving on the highway, where i keep it around 60, my truck stalls when i slow down. I get to the intersection at the end of the offramp, and when i come to a complete stop, it just cuts out.
Fires right back up, a little weakly, but drives away fine enough.

Any thoughts?

 

Sounds like an EGR problem to me. They will hang up and as soon as you loose vacuum when it stalls they will reset.

 

you think it is staying open?

 

cheapest i can find one around here is around 150.

im going to remove it so i can see if it sticks.

if i drive it without the egr (and block everything off) out onto the highway to recreate the conditions of it stalling before can i hurt anything? I know egr reduces the temperature in the cylinders so i dont want to blow anything up.

 

Yes I think your EGR is sticking in an open position. I made a plate to replace the EGR and seal off the opening just for testing. If it cures the problem with the plate in place you have isolated the problem to the EGR system. If this fixes the problem it could still not be the EGR itself but a sticking solenoid. To isolate the solenoid disconnect the vacuum line at the EGR and plug it. If it cures the problem it is probably the solenoid. My truck has 3 solenoids so I just change wires and the vacuum lines to another solenoid to see if it fixes the problem.

 

before i did that i decided to check the MAP sensor (because it monitors and adjusts for changes in speed, which are the locus of my problem). heres what i found.

I was reading OK voltages without vacuum (5 volts, as per the Haynes). when i ran the truck and checked the voltage it was supposed to be between 1.5 and 2.5 volts. I was getting 1.5 bang on at idle, but when i revved it the voltage jumped around from .8 to 2.3.

Any thoughts on this?

 

MAP sensors don't really monitor speed, they actually monitor engine load by measuring vacuum. The MAP is best tested with a hand vacuum pump for better control of the vacuum as it is applied. As you slowly and smoothly apply more vacuum the voltage should change smoothly. Any jumping or jerking in voltage or loss of voltage as the vacuum is applied will result in drivability problems. Smooth is the operative word here. The MAP is a variable resistor that changes voltage according to vacuum change ie engine load change. The range of 1.5 to 2.5 at idle is because resistors are all different and can change with heat and age. The actual voltage numbers are not really important but just guidelines for testing. The change tells the computer what load the engine is under. The smoothness of the change is what you must look for.

 

well my logic was that if the MAP is measuring the load wrong then itll throw of the engine. it seems fine though, smooth like you say it should be. I checked the EGR and it also seems ok. i dont always trust the guys at the parts desk, but he said it could be cause by the torque converter clutch soleneid cause the TC to stay locked up. I dont have an OD tranny, just a 3 speed. I dont know much about transmissions, (i cant find the TCC in my haynes) what do you think?

EDIT
i meant the lock-up control solenoid. My haynes just says its on some models and not others, without telling me where it is or what voltage i should see

 

Mine doesn't have a locking torque converter. My understanding is that if it doesn't unlock it would stall the engine when you stop. I have no manuals on it either. Try shifting the truck into neutral just before you stop. If it is the lock up the truck will continue to run when you stop in neutral. If it is an engine problem it will still quit in neutral when you stop. If the truck continues to run you may want to shut it off before shifting back into drive or you may damage your tranny.

 

ill try that. ive unplugged the part throttle unlock relay for fun. well see what happens tonight when i take it on a 30 minute highway run

UPDATE. removing the PTU relay made no changes for better or worse. i discovered that is because the relay is broken, im not measuring the 75 ohms in it im supposed to. dealer is looking for a new one. I dont think it is related to the stalling issue though. The reason i removed it was becuase i was thinking it was the torque converter lockup relay, and had a suspicion that the TC was not unlocking after highway driving and this is why it stalled. im not sure if my truck even has a lock-up TC (91 318 w/3speed).

im gonna have to sell my truck if i cant fix