I'm he original owner of an 85 EFI SR5 4x4 truck. It's not my main vehicle and it hasn't been driven a lot in the last year or two due it not running good and also needing front knuckle rebuild and tires. A new TPS plus setting the timing got it running 1000% better. I finally got tires and knuckle rebuild done last week and now it has mysteriously started randomly dying on me. At first I thought it was bad fuel. I add stabil because it sits a lot and I added some fuel dry thinking maybe it was condensation build-up. You can be running along no problems at all and then it acts like you either shut off the fuel or the spark. Sometimes it will come back to life before it coasts to a stop of left in gear and ignition on...like bad gas If not then it usually starts back up after 6 to 10 tries and then runs like a champ. It will also do it sometimes on first start, like tonight Go to store, turn it off, come out and it won't start Today it died while my daughter was with me so I was able to test a plug wire. It was getting a small spark, nothing like when running though I was testing when it finally kicked over and it was easy to see that the spark was much stronger when it started up. Is that normal operation?

I don't really know if I have a fuel issue or an ignition issue. I had to fill up the tank today so it was 100% full of fresh gas when it happened this evening. It's been a long time since the fuel filter was changed so that is first on my list. The plug wires are pretty new as well as distributor cap and rotor.

Where should I be looking next and how do I test for it?

 

How many volts are you getting on the battery?
Could be your battery going out if the spark isnt enough to keep it going.

 

I'll check that but due to the randomness of it happening and it dying while driving, I don't suspect the battery, but worth ruling out for sure. I keep it on a battery tender when parked due to the infrequency I drive it.

 

Any stored trouble codes?

Could be a loose connection at the AFM:
- http://www.4crawler.com/4x4/CheapTricks/AFM/index.shtml

Try this and see if it helps:
- http://www.4crawler.com/4x4/CheapTri...shtml#FuelPump

Also, might try simply pulling, inspecting and replacing all the fuses in the various fuse panels. I had my '85 die once and doing that (and finding no bad fuses) fixed the problem and it has never done that since. Suspect I had oxidation on some fuse connector and the re-seating of that fuse cleaned off the contact.

 

Hmmm. fuse change is pretty easy. that may explain my mystery dash light problem where they don't come on with the light switch but come on randomly after I start driving.

 

check the pickup inside the distrubutor. you need an ohm meter, simply disconnect the wire at the distributor connector and resistance should be 140 to 180 ohms

 

I shorted out the fuel pump check connector and I've gone through one tank of gas with no random dying. it would have died several times by now. So, that seems to point to a malfunctioning fuel pump switch in the mass air filter. I guess I'll just pony up the $140 to buy a referb one

 

[QUOTE=DanDanTMM;51841595]I shorted out the fuel pump check connector and I've gone through one tank of gas with no random dying. it would have died several times by now. So, that seems to point to a malfunctioning fuel pump switch in the mass air filter. I guess I'll just pony up the $140 to buy a referb one[

if thats the case, check the circuit opening relay as well......

 

Almost sounds like the reoccurring German car disease, bad fuel pump relay. Or something in pump circuit. Possible lost ground from being parked?

 

[QUOTE=aalba92691;51841598]Wouldn't it still be dieing if it was the COR? The fuel pump check connector only bypasses the Mass Air Sensor fuel pump switch. I'm going to remove the jumper from the test switch and see if it dies. If it does and I jumper again and it quits, that pretty much tells me mass air sensor fuel pump switch.

 

*** UPDATE ***

So i ordered a rebuilt MAS from www.rockauto.com (great prices by the way) and my random dieing problem is no more. It also runs even better, which is surprising after the difference the TPS made. I compared the old one to the refurb and the flap in the original is harder to open. The ever so slight hesitation it had starting out in 1st is gone. I can also tell that it has more power because i'm not bogging down in 5th as much now. Plus, my gas mileage seems to have improved.

Now i just need to find where that faint antifreeze smell is coming from... It is probably time for a complete hose replacement.