This Expy has had this problem for weeks now. Already changed the fuel pump and strainer and fuel filter. The fuel pressure is 34 regulated and 40 unregulated(vacuum hose removed from regulator). Crank sensor was just changed too. The engine shuts "OFF" intermittently. It might go a week and then it might do it twice in one day. Fortunately it has always been on city streets and not on the interstate as highway speeds. It always restarts with no problem which is strange. The owner says the dash lites and radio are still working when the engine stalls. She said the last time it happened the steering locked, but I'm not convinced about that one. Everytime I've driven the vehicle it works perfect. It never shuts "OFF" for me and doesn't miss or hesitate so I haven't been able to see the symptom when it actually happens. I hope someone has a suggestions on this one because I'm guessing at this point. I also did some Voltage Drop checks, but didn't find any that were significant. I cleaned all the HOT teminals and grounds I could see. I did the BATT POS and NEG, HOT terminals on the starter relay which is also used by the ALT. output wire and supply wire the goes to the fuse box as well as all the ground straps I found. I didn't clean the main ground terminal coming from the BATT NEG. post to the block or chassis because I could only trace it part of the way before I ran out of time. Please HELP!

 

It sounds like a system failure like all the cops loose their signal at the same time. If it were one or two of the cops, then the engine would miss, not shut down. Looking at my ignition schematic, the subsytems that would kill the engine if they went bad are (discounting fuses) the crankshaft position sensor which you've alread replaced, the PCM itself, PCM power relay, and a PCM power diode. I would suspect that the diode is over heating and opening momentarily which would shut the engine off. Once the diode cools, the engine would restart. Unfortuantely, the schematic doesn't list the location of these modules.

 

Are the PCM diode and relay located in the underhood fuse panel. I don't have the vehicle here, but I assume that's where they are located which means I can use the swap method to eliminate those two as my cause. The last time I looked at the fuse panel I saw a couple of diodes beside each other. They each had one terminal facing N/S and the other E/W so the polarity couldn't get reversed. I can swap those and I'll have to find the PCM relay. It has to be low current unlike a relay that controls a motor. Thanks sbclemens for the suggestion. This Expy is starting to make me look like I don't know how to troubleshoot. I'm fishing at this point. When I see this Expy in the morning I'll sway the diode and relay.

 

I still haven't found the power diode on my '98. The schematic shows a red/lt green wire coming from the #30 fuse (under the dash) that t's off. One side comes from the coils and the other goes to the diode. The wire exiting the diode is white/lt blue. This last wire runs to the PCM power relay. Hope this helps. I'm been meaning to buy the factory schematics. Maybe nows a good time.

 

I found the User Manual and located the PCM relay and diode. The PCM is monitored by fuses 2 and 18. It is controled by Relay 304 and Diode 501. These are located in the underhood fuse panel. I swapped the PCM diode with the A/C clutch relay(502 with 502). Next I'm going to swap the PCM relay. I plan to try 302 with 304. That's the trailer relay(which is never used on this Expy) with the PCM relay. We'll see what happens

 

Sounds like a good plan. Keep us posted.

 

Any update?

 

No phone call yet which is good news because when the phone rings she is calling to tell me it shut off. That's been 4 days now which is good. If it reaches a week or 10 days I think we are out of the woods. I swapped the PCM diode with the A/C clutch diode and the PCM relay with the windshield relay and told her to watch for any strange symptoms from the A/C or wipers. I know she will be using the A/C all the time, but it may be a while before we get some rain to try out the wipers. I'd like to see a malfunction of either the A/C or wipers so I can point to either that relay or diode as the cause. This would just be a confirmation for me, but it would help other people with this problem in the future fix their problem quicker which is what this forum is all about.

 

Any Updates?

I have a 1999 4wd 5.4 and have been having the same problem. It always stopped on my wife. Today it stalled on me when taking off. I replace the cam sensor. Just grasping at straws at this point.


I replaced a cop on #3 cylinder a month ago. it ran real ruff on and off for a few days before it threw a code. Replaced and in a week the same problem.

This one was my fault. When installing a cop be careful the the connector is on going to hit anything when the engine rocks during acceleration.

 

Today makes one week with no failures. It never went that long before without shutting off. The cam sensor won't cause your problem, but the crank sensor could. This Expy did NOT have a DTC so I had to go fish. I tried the fuel filter(which needed to be changed anyway), the fuel pump and strainer(pressure was 24 lb. about 6 lb. low) and then the crank sensor. At that point I was really stumped. I got a suggestion to try the PCM diode and PCM relay which I did. I swapped them both at the same time so I don't know which one it was. It would be nice to know to help other people with this random stalling problem, but I was so desparate for a fix I did them both at the same time. You can do them one at a time to see if you get different results than I did. One week and counting so I'm not complaining. You have a DTC so you need to follow that path, but if you have random intermittent shut off problems you might consider the diode and relay.

 

If the AC and wipers don't draw the same current as the ignition system, the diode and/or relay may not open, so I would suggest calling the lady but then, you'll probably jinx it!

 

Considering the wipers have a motor and the A/C has a electromagnetic clutch I would think they both should draw more current than the PCM which has no motor or clutch coil. I'm waiting for her to tell me she has had problems with either the wipers or A/C, but so far everything is working. I told her to monitor them when I switched the diode and relay so in this case no news is good news. If anyone has this problem this is worth trying before you swap the crank sensor which requires dismounting the A/C compressor. Swapping the diode and resistor is less than 5 minutes to swap.

 

I have swapped the fore mentioned diodes and relays. The engine stalled again today. My wifes says it seems to stall and hesitate then starts running ok. I guess I will change the crankcase sensor this weekend.

 

Read eallanbogg's thread on changing the crank sensor. The sensor is located in an area that gets caked with road grime, grease, etc. Try cleaning the sensor and the connector first.

 

...and please start a new thread. It doesn't sound as if the issues eallanboggs had are the same as yours. With a new thread started, you'll probably get more help.