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Unread 08-02-2007, 07:15 PM   #1
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Default 1985 F150 with cold running probs

I have a 1985 F150 with the 300CI six, fourspeed overdrive manual. When warmed up, she runs about as good as she can for 195K on the clock. Starts on the second turn, stays running, no major missing or anything. When cold, however, it becomes quite finicky.

Sometimes, ittl fire up and go as if it were warmed up. Sometimes, when it starts, it sounds and feels like it's only hittin on 3 or 4 cylinders, then the remaining duds finally come online and off it goes. However, before it warms up, it misfires and stumbles when you abruptly give it gas. It will, however, spin right up without a miss if the throttle is gradually increased. This goes away when the temps come up. If it's in third or fourth gear, cold, and you give it sudden increase, it will acually completely die, throw you forward as if you had brakechecked, backfire and restart. Sometimes, this is accompanied with tirechirp. One day when it was paticularly ornery, I performed a power balance test and found that number 5 is barely hitting hard enough to make a sound. No RPM or smoothness change when that wire was disconnected, just an audible change in the exhaust note.

Other times, it just flat refuses to start. Took me 5 minutes straight to get it lit off one time. Again, once it's started, it wont stall and once warmed up, runs like a champ. When it's this much of a pain to get lit off, it usually behaves once it starts. It's only done this once so far.


Sometimes, hot or cold, it dies in corners. Right hand turns are the hardest on it. Other times it only sputters and misses, most of the time tho it just thunders on down the road as normal.


The last emissions check it had, which was taken while it was doing this, showed 35-40 HC's, 0.00% CO and ~20% CO2 at the tailpipe. I hesitate to trust this, however, as it's always had an exhaust leak. Post-test, one of the backfires from a stall acually blew a chunk out of the top of the muffler, giving it a nice growl and hardly any gases making it out of the tailpipe. I wonder if this is gonna fail it come January...


Any of you know what's going on under my hood and about how expensive the parts will be?
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Unread 08-02-2007, 07:42 PM   #2
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That happened to my jetta once, turned out it was the distributer was going so it wasn't igniting the spark plugs all the time. It stall out randomly while driving in the city etc. It could also be your wires or actual plugs, or even the distributer cap. I found out it was the distrubiter by jiggling the wires attached to the cap when it wouldn't start.
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Unread 08-03-2007, 04:01 PM   #3
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1985, hmmmm. I think that's one of the first years of EFI on the 300. I've seen various sensors and such cause similar problems on early 90's fords. Could be the coolant temp sensor reading too high causing a lean condition, egr valve sticking open, bad grounds to the engine or body, computer just wacko, throttle position sensor, ignition module, pickup coil, plugs, wires , cracked distributor cap, probably other things I can't think of at the moment.

The bad part about diagnosing fords is the early computer systems didn't store trouble codes, they won't give you a code unless the fault is there all the time, or it happens when the test is running. If your lucky the Key on engine off test will throw a code, because the key on engine running test requires that the engine be at normal operating temp(the Koeo test may, don't really remember). If that doesn't work the only way to find the problem is to test all the sensors with the engine cold, as there is no datastream capabilities on the early fords either.

So you might want to consider having it professionally diagnosed, by a shop that you trust. Or you could throw parts at it, might get lucky, but that approach never works for me.

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Unread 08-03-2007, 06:34 PM   #4
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Mine has the 1BBL electronic carb on it, and an EEC-IV computer, if that's any help. If I blip it a few times before I attempt to start it, it forgoes the hard starting, but still misses untill it's warmed up.
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Unread 08-03-2007, 07:04 PM   #5
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Well, since your truck has a carb, I would say probably a vacuum leak, egr valve stuck open a little, but most likely a problem in the electronic part of the carb. It doesn't really sound like a mechanical problem with the engine, unless the compression rings are marginal. I've seen that happen one time on a chevy 366. It would not start when it got below 20F, but ran fine once it warmed up. It really sounds like it's running way to lean when cold. Maybe a carb rebuild would help, might be some trash in a passage that adds fuel when the engine is cold. Or if it's possible to do it, maybe put an older model carb on without the electronics.
Next time I'm in town I'll ask a friend about it, see if he's ever run onto a problem like this, since he worked at a ford dealership in the mid 90's. He might have a few ideas about what it could be.

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Unread 08-10-2007, 10:18 PM   #6
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Something new popped up yesterday. Apparently, my float is getting stuck down. I fired it up and it pissed a quarter gallon of gas all over itself and blacksmoked like a diesel. Knocking on the carb made it run right and quit spewing fuel out of the vent. Would this be another signal that the carb's getting flooded with trash or is that just a sinking float?
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Unread 08-13-2007, 07:06 PM   #7
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sounds like you need a new float with a carb rebuild. It's probably trash in there causing your running problems.

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