2.5 starts but will not idle or run >1min

[Mcstiff]

Like the title says, it shuts off after 1 min or less and will restart after a few tries. It runs fine untill it dies. Seemes to be getting fuel (changed the filter today) and the accesseries stay on so its not power. I'm going to check the plugs, wires, cap, and rotor tomarrow.
Any ideas on things to check?

[Matthew Currie]

Is there a ballast resistor for the fuel pump? Some 4.0's have that, and if that's bad or poorly connected it will start but not stay running.

[Ghost]

Carbed, TBI or MPI? Each has a different system both fuel and electrical.

[rixXJphx]

Check the venting of the fuel tank.

If the tank is nearly full, there's not much air in it. If the vent lines (from the filler neck IIRC to the charcoal canister) is blocked or crimped, then the removal of a little fuel causes a 'vacuum' against which the fuel pump can't suck.
Eventually, enough air leaks into the tank to eliminate the 'vacuum'.

Most prevalent on carb'd engines, where the fuel pump is a low-pressure unit sucking from the engine as opposed to a higher-pressure FI fuel pump 'pushing' from the gas tank.

[Mcstiff]

It is TBI with no resistor. If I try running it w/o the gas cap will that tell me if it is the vent?

[Mcstiff]

Well no luck w/o the cap :mad: Checking plugs and wires tomarrow. Any other ideas?

[gettinbetterXJ]

maybe the vacum lines, I had a similar problem only it would start and run like CRAP until it died in a minute or so popped open the hood and there to the right of the fuel rail there is a little cluster of vacum lines two of them had come off for whatever reason while it was running I put them back on, idle calmed down , ran great haven't had the problem since. Wish I could be more technically informative as to what those are but I'm still learning.

[Mcstiff]

Thanks I'll look for somthing like that but I dont have a fuel rail.

[sternbal]

I'd look for something like an EGR valve stuck open or perhaps a bad TPS. Your setup has an Idle Speed Actuator motor which will usually keep the RPMs high for several seconds when it starts. It could be that when the RPMs drop back to normal, they're insufficient for idling. If at idle I push in my EGR or mess with my TPS, it will stumble, and sometimes die. The MAP sensor should probably be checked too.

[Mcstiff]

Replaced the vac line to the MAP (it was cracked) and now it will not start. I'm going to test the MAP, TPS, and EGR tomarrow. I'm thinking that this is a spark problem because it will not fire up even with starter fluid.

[Ghost]

Go get a spark tester from the auto parts store. They are less than $20 and really help diagnose spark problems.

[sternbal]

Will it start if you redisconnect the MAP to create a vacuum leak?

[Mcstiff]

I havent tried it with the MAP disco's but it did start agan, died after 40sec, and will nto restart right away.

[Mcstiff]

If you had to pick which of these sensors would stop the coil from sending spart to the dist.?

A: MAP
B: Crankshaft Position
C: Somthing else

[sternbal]

The CPS would be my first guess. You could also be looking at a faulty ignition module. MAP shouldn't affect the spark.

[HossHoffer]

You said it dies after a few seconds. Can you get the rpms to come up before it dies? I mean can you rev it a little before it dies or does it just shut off all of the sudden no matter what the rpms are turning? Is there any raw gas smell? Mine 2.5l acted somewhat the same when my fuel pump was dying. It got just enough fuel into it to start for a few seconds but not enough to run. Check your pump for proper pressure or it it is running at all. Good luck!:)

[Mcstiff]

Does the '86 have a ignition module? My POS chiltions says 87+ has the ignition module. My guess is the CPS.
The RPM's do not make a diffrence. I used a spark tester between the coil and dist it seemes like the coil turned off before the engine.

[sternbal]

The ignition module will be integral with the coil.

If you're sure its spark and not fuel, and you say you've already checked the cap, rotor, plugs, wires, then the only things left are the CPS, module/coil, ECU and wiring inbetween.

However, as HossHoffer pointed out, it isn't a bad idea to rule out fuel being the culprit before going and spending money on replacement parts. There is a pressure test point on the side of the throttle body. Remove the plug and I believe its a 1/8 npt fitting. You should have about 15 psi.

[Mcstiff]

I know it is not the fuel. It will not start with starter fluid so that pritty much rules out fuel and points to spark