'95 TBI Misfire?

[gothicsera]

My truck's developed a bit of an issue and I was wondering if anyone has had something similar before?

'95 K2500 5.7 TBI

It starts and runs just fine when its cold and it's ok when it's hot too. No problems. But if I stop and leave it parked for 30 mins or so and then fire it back up it has a misfire at idle, it will nearly die and then pick back up again. If you drive it then it intermittently feels like it has no power and then it will surge as it starts running right again. After a couple of minutes driving it clears up and runs perfectly again until you park up.

From a cold start it's fine.

It's not throwing a CEL or anything when it's got the symptoms.

Anyone have any ideas? I was thinking possibly a bad coil or injector connection?

 

[TylerZ281500]

starting ohming out sensors at the computers connector otherwise your just guessing

 

[east302]

Have you done a fuel pressure test?

 

[gothicsera]

Where is the pressure test point on these motors? I do have a gauge...

I had a prod around this weekend, rotor, leads and cap all look OK (and are only a few 1000 miles old).

I ran it until hot and then restarted it and it was acting up. Injectors looked to be firing OK. I unplugged the idle valve while it was acting up and it made no difference.

I went to it this morning and it was very reluctant to start - which is the first time it's done that. After trying a few times it fired up OK.

 

[east302]

I don't think that the TBI had a Schrader valve, so you have to put the Gauge inline somewhere...probably at the fuel filter or up at the TBI unit.

Are you getting spark at all cylinders when it's acting up? That could rule out ignition fairly quickly.

As a quick check, test the resistance of the coolant temperature sensor. It should change with temperature, a failing unit can cause hot start issues. Check a manual or online for the correct resistance vs temperature values. I'm not sure where it is on the TBI, but it's by the thermostat on the vortec models.


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[Breakdown]

The coolant temp sensor is next to the thermo housing on the tbi's as well. If it was carb'd I'd say it sounds almost like vapor lock with the fuel lines....

 

[gothicsera]

I've swapped the temperature sensor for a brand new one and it's made no difference to the problem.

Cold start is OK (apart from it not wanting to start at all earlier in the week it's been fine since)

Hot it runs OK. Until you shut it off for about 30 mins and then restarts. After that the engine speed hunts and it will die if you leave it. If you keep it running it settles down after about 5 minutes and will run fine again until you shut it off.

It's weird...