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Stalling / backfire right after startup


Darel

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'86 BII 5sp

Having an annoying issue with my BII. When you go and start it cold, it will start and idle fine. High idle is OK, normal idle is fine too. However if you try to drive the truck anywhere, it just won't. It will gag and sputter and misfire, and backfire too under a load. Clutch in / no load and it idles and revs fine. Only when it's got a load on it.

However, this is only for the first 5 minutes or so. Once you manage to stumble a quarter mile or so, it'll be A-OK and run fine all day long, around town and highway driving.

So far, I've replaced the IAC and the coolant temp sensor (for the ECU). When I first got the truck two years ago, I also gave it a full tuneup and replaced the distributor with a reman unit, keeping the original Ford module because the generic module that came with the reman dizzy was bad.

I will also note, sometimes I get some gray/black smoke from the exhaust. Like, at first start, and when it's sitting idling for a long time - for instance, when I was charging up the A/C and it basically sat in my driveway idling for about two hours.

Any thoughts?

Thanks,
Darel
 


Darel

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Replaced fuel pump last month. New filter when I "recommissioned" the truck two years ago, no crud in tank when I replaced the pump. Also, it'd be worse when warm / floored and it's not. I'm not ruling out some sort of injector issue (more likely an injector control issue) but there's nothing that tells me the fuel system is bad.
 

Darel

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I should note, I am no stranger to brand new parts being bad out of the box, however the truck has done this since we've had it, and no changes I've made have had any effect at all. Could it be a timing issue? The backfire leads me to that.
 

littlefoot

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yeah if its the timing it could even just be an issue with the timing belt? unless you've changed that already as well?
I should note, I am no stranger to brand new parts being bad out of the box, however the truck has done this since we've had it, and no changes I've made have had any effect at all. Could it be a timing issue? The backfire leads me to that.
 

Darel

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These have a timing chain.
 

JerryC

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Thinking out loud...
First five minutes bad, then good - open loop issue then 02 sensor warms up and goes into closed loop and can correct fuel issue. So where is the problem? bad temp sender (replaced but not new at this point) or TS wiring, vacuum leak, TPS issue (could maybe be carbon buildup in throttle body keeping the blade from fully closing, ACT sensor???

Is the smoke part of the problem? Black smoke=fuel, grey=oil. If fuel, I'd look first at dirty injectors..
If grey, then I'd guess valve seals. Oil seeps in as the vehicle sits and will also build up in valve cover as the vehicle idles (probably lots oil gunk on the head slowing the return flow oil (my 86 had this issue).
 

Darel

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Hmmm.....vac leak. That's a possibility. What in the vacuum circuit is open in that first few minutes but then closes off?
 

JerryC

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Hmmm.....vac leak. That's a possibility. What in the vacuum circuit is open in that first few minutes but then closes off?
It's not that the vac leak goes away, but that the 02 sensor sees it and calls for more fuel to fix the lean condition. When I got my current BII a few years ago it had several small vacuum leaks through dry rotted hoses and bushings. I found those and then later the upper intake gasket cracked from old age (it made almost no power when this happened).
 

Darel

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Gotcha. Believe it or not I actually did smoke test this a month or so ago when it was acting up and didn't find anything, but I also didn't really put a lot of effort into it. I'll have to dig into that a little more. Thanks!
 

JerryC

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Check the ACT, Air Charge Temp sensor on the passenger side of the intake. It may be bad or just covered in goo.
 

Darel

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For $8 I just ordered a new one. Not even worth my time taking the old one out without replacing it. Will update. Thank you!
 

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