87 f-150 300 6 cyl missing and dies at idle?

[kpyro]

Ok I'll try and give as much info as I can about my problem I hope someone can help me. I have a 1987 f-150 300 6 CLY that starts right up and then dies after a few seconds unless the throttle plate is opened slightly. It also stumbles off idle and has a miss. If I play with the throttle a while I can get it to settle and idle sometimes. If I remove a cap from the intake manafold vacuum it will idle but still misses. Intake vac is about 16-17 in and does not fall at high rpm so cat is ok? The TPS tests good. I have cleaned the (idle bypass sol.) and it seems to be functioning Should this seal completely when no signal is applied? When I take the SOL off the valve will close completly but when I put it back on I can see the SOL plunger pushes the valve open slightly. Plugs look ok slight spot of redish area otherwise clean. KOEO 11 pass 11 pass CM 87 Fuel Pump CKt 33 EGR Pressure tested ok I dont remember valu but it was good EGR is probably junk. (KOER was done with vac leak it was the only way to keep it running for test) KOER 41 No HEGO switching detected always lean (SOMETIMES) 44 Thermactor Air Injection system inoperative (ALWAYS) I havent measured the out put of the O2 sensor yet but it shouldnt be in play when the engine is cold anyway. The air pump was shot even before I got the truck. Anyway any ideas here ? I just realized I forgot to test the ACT sensor I will check that if I can find it. Thanks for any help. Ken

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[Bluegrass]

My basic assumption comes from your OX sensor code. I tells a great deal about the root cause.
An alway lean is telling that the engine is detected as running rich.
Just the oppisite of what you may think.
It means the computer fuel tables are shifted lean and not the engine.
How does it get to running rich?
A. air leak into the intake, after the throttle body.
B. fuel regulator diaphram leaking into it's vacuum hose.
C. fuel pressure to high.
D. leaking injectors.
E. possible air leak into the exhaust ahead of the OX sensor.
Any one or more of these conditions are detected by the OX sensor to the point it no longer can switch in it's normal way because it it always out of range to much fuel in the exhaust gas (cool).
A cold start should go high idle then come down as the engine and exhaust heats up.
If this is not happening to begin, there may be more than one fault present at the same time..
Cold start opens the IAC to provide air. If there is a leak besides, it may close down and not contol the idle because there is no other way to do this.
At the same time the fuel is rich because the ECT and ACT has signaled the EEC to do that due to the cold temp.
This is all accomplished at the time the ignition switch is goes from OFF to RUN, then to crank.
Make a good investigation of every area where hoses, gaskets and mating surfaces could be open to air.

[Steve83]

Read this diagram & its caption.



Then try to determine if it applies to you. IIRC, there was another recall that affected many 4.9L EECs.

[kpyro]

Originally Posted by Bluegrass

My basic assumption comes from your OX sensor code. I tells a great deal about the root cause.
An alway lean is telling that the engine is detected as running rich.
Just the oppisite of what you may think.
It means the computer fuel tables are shifted lean and not the engine.

Yep I had that figured just backward.

Originally Posted by Bluegrass

How does it get to running rich?
A. air leak into the intake, after the throttle body.

Remember I had a vac hose cap off so it would stay running for the KOER test
so that may be why I got that code.

I'll check the other options as well.

Originally Posted by Bluegrass

A cold start should go high idle then come down as the engine and exhaust heats up.

At cold it starts and sounds like high idle for 1-3 seconds then falls and soon dies. I usally can't make it out of the truck to get my hand on the throttle to keep it running before it dies.

Originally Posted by Bluegrass

If this is not happening to begin, there may be more than one fault present at the same time..

With this truck I would bet on it

Originally Posted by Bluegrass

If there is a leak besides, it may close down and not contol the idle because there is no other way to do this.

During the KOER test it does seem to be able to control idle it raises it and lowers it during the test. If I can get it idle long enough to get into the test mode with the VAC cap on it will raise and the when it lowers the idle just before the dynamic response test it always dies.

Originally Posted by Bluegrass

At the same time the fuel is rich because the ECT and ACT has signaled the EEC to do that due to the cold temp.

I need to check both these with a meter and post results.

Thanks for the input I will get back to it soon and see how far I get.
Thanks
Ken

[kpyro]

Originally Posted by Steve83

Read this diagram & its caption.
Then try to determine if it applies to you. IIRC, there was another recall that affected many 4.9L EECs.

I'll look and see if it has had the update. I havent messed with the timing yet I couldnt find timing marks it has a tube where I thought the plate should be.

I have alway thought this truck ran RICH attaching a trailer with it running would burn your eyes like crazy lots of (I assume unburnt fuel fumes) but no black smoke though.

That EEC "training" procedure may be useful.

This truck doesnt get driven much 5-10 times per month 10 mile or less trips.

Thanks
Ken