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post #1 of (permalink) Old 01-29-2007, 11:27 AM Thread Starter
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Idle problem and miss/stumble/stall at altitude

1990 K-1500 Z-71, 350 cid, 700r auto, California Emissions
Rebuilt motor by local shop (known as a good one)
New distributor, coil, plugs, wires, fuel & air filters, 02 sensor,
Problem #1
Rough idle, seems to be "hunting", almost like a big cam at low idle. Starts fine and seems to be ok while on 'fast idle, warm up' but goes to heck after warmed up.

Problem #2
at approx 5000 elevation it has a miss/stumble/stall.
I live at 7000 ft and the problem occurs everytime at nearly the same location on the drive home from the valley (150 ft elev, 90 mile trip). The problem goes away after a few miles/minutes.

Three mechanics have looked at this, scratched their heads and don't want any more to do with it. (speed shop, smog station, tune up shop) All seem to think the computer needed to 're-learn' and to drive it awhile and see what happens. Some improvement but not much.

Need this cured because it Smog test time, actually overdue!
Thanks for any help, thoughts, suggestions. Or any other BBD's to post on?
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post #2 of (permalink) Old 01-30-2007, 07:42 PM
 
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Re: Idle problem and miss/stumble/stall at altitude

Yea. It sounds like your Controll module is relearning...
I have had a couple vehicl's that did that after the battery was disconnected for more than 30 seconds.
It suposedly takes 500 -100 miles for it to completly sync.
If it doesnt seem notably better after a week disconnect the battery so it starts over... Had a ford ranger that started blowing black smoke cause of this and once it started over all was better.
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post #3 of (permalink) Old 02-03-2007, 07:47 PM Thread Starter
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Re: Idle problem and miss/stumble/stall at altitude

Ok, here is what we found today, no codes in the computer.
Fuel pressure, sensors, TPS, O2, MAP, air flow, timing, plugs, distributor and injectors are all good! We even replaced the computer with a known good one.
Mechanic is at a loss (third one to check this out). He thinks with all electrical & fuel issues accounted for that the problem is mechanical, most probably a "tight valve".
Anyone ever heard of this? New one on me??
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post #4 of (permalink) Old 02-04-2007, 03:09 PM
 
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Re: Idle problem and miss/stumble/stall at altitude

Not sure if I buy the Tight Valve.... Easy to check tho.. Just do a compression test.. If you find a notably low reading on one cilinder then he is most likely right... Make sure you do it with the engin warm.
Still sounds to me like the comp is going through its learning curve hence the no codes... You might check the vaccume to...
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post #5 of (permalink) Old 02-05-2007, 09:26 AM
 
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Re: Idle problem and miss/stumble/stall at altitude

Another thing to check is your grounding. Sence your motor has just been out make sure all the ground straps got put back on and if they are missing or in real bad shape replace them, also make sure tey are tight. This is what I would lean tword first.
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post #6 of (permalink) Old 02-05-2007, 01:11 PM Thread Starter
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Re: Idle problem and miss/stumble/stall at altitude

I thought of the ground and installed an addition temp ground but no luck.
I was able to talk with the mechanics in person this morning (last time was on the phone relayed to me by my son-in-law).
Both are POSITIVE the fuel & electrial systems are good. That leaves vac leak or mechanical problems.
I'm thinking that the intake manifold is a 'full seal' and there may be a crack or leak on the underside? How do I test for this? Plug/close the PCV valve and flood some propane into the area via the oil fill cap? Any hazard to this?

Thanks
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post #7 of (permalink) Old 02-05-2007, 09:02 PM
 
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Re: Idle problem and miss/stumble/stall at altitude

There are a couple things you can do to check for a vaccume leak. You can buy a vac guage and hook it up at idle you should see around 18-22 in.Hg. Anything below that is a problem. Also make sure you are not connecting to a ported vaccume.. Use the break booster line for the most accurate results.
For external stuff like hoses and lines you can hit them with a shot of either..(Starting fluid) you should get an almost imediate miss.. Make sure and use the either sparingly as it is VERRRRY flamible...(Yes I have)..lol
Lastly try the compression test on the cylinders...
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post #8 of (permalink) Old 02-06-2007, 03:55 PM Thread Starter
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Re: Idle problem and miss/stumble/stall at altitude

OK, it passed the smog test today with no new changes! At least that is taken care of but still not idling right (surgings to nearly stalling) and I left it down in the valley this week, so I don't know about the altitude problem.
Family problems this week, so I'll have to put this on hold for awhile.
It's been on the dyno twice.
It still surges with the computer disconnected (connector on firewall).
Thanks for the input guys.

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