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post #1 of (permalink) Old 08-20-2003, 06:58 PM Thread Starter
 
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bad idle and miss after engine warms

hello, well i have an 88 zuk that is still running stock carb. the problem is that when the engine warms up, it loses its idle and hesitates badly. if i let it sit over night it will start, run and idle fine until i take it for a drive. after it starts to warm up, it will stumble and die. runs ok if i keep my foot into it and keep it reved up.

it has a nice sequential spark on all 4 cylinders, and the timing belt is dead on with the timing marks. fuel pressure is fine. so far i have done the following:

-swapped in two different distributors
-swapped on 3 different stock carbs, one was pulled from a good running zuk so the carb was good
-swapped in 5 different carb ecms
-swapped in 2 different coils
-i played around with unpluging all of the electrical items one at a time on the feedback carb, none helped
-checked for vaccume leaks with carb cleaner, none detected
-replaced fuel filter
-redid the grounds in the engine compartment.

i have a feeling that there is an electrical issue on one or more of the wires leading to the feedback carb. my next step is to install a full MECHANICAL carb such as a weber. if that doesn't work, i will assume i have a compression problem

what the hell am i over looking??
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post #2 of (permalink) Old 08-20-2003, 07:22 PM
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Re: bad idle and miss after engine warms

If you think it is compression I believe I do a compression check. But sound more like the carb to me, either rebuilded or replace it.
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post #3 of (permalink) Old 08-20-2003, 07:34 PM Thread Starter
 
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Re: bad idle and miss after engine warms

thats what i thought too. i pulled a stock carb off my bro's zuk (which ran fine cold or warm) and installed it on my zuk. started, ran, and idled great until i drove it and it warmed up, then it still had the same problem with it not holding idle and bad low end hesitation/miss. when the same carb is on my bro's zuk, it runs fine and does not exhibit the same problems as it does when it is installed on mine. i am at a loss and i do very much appreciate any reponses anyone might have.
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post #4 of (permalink) Old 08-20-2003, 07:49 PM
 
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Re: bad idle and miss after engine warms

When you said 2 coils tried, were either of them new? I have 2 bad ones that run, but inconsistantly.
Sami's seem to eat coils.

It's worth while to replace the coil with a good accell or equivelent.
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post #5 of (permalink) Old 08-20-2003, 08:25 PM
 
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Re: bad idle and miss after engine warms

Intake manifold gasket leaking
Exhaust leak......possibly the gasket or a defect in the pipe on the engine side of the convertor.
Bad plug wires.
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post #6 of (permalink) Old 08-20-2003, 08:50 PM Thread Starter
 
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Re: bad idle and miss after engine warms

in response to the coils...no they were not new. to be honest they came out of a FORD spare parts bin. i too have experienced inconsistant coils before. temp changes do effect a weak coil don't they...that slipped my mind until you brought this to my attention. now you got me anxious to pull a coil from one of my GOOD running zuks and give it a test, which i will do tomorrow.

i sprayed the entire carb/intake area looking for vaccume leaks and i did not notice any rpm change when spraying it with carb cleaner. i sprayed fairly heavily as i was concerned about the 12 miles of vaccume hoses. if i could ever get teh thing to idle slower, i would run my vaccume guage in an attempt to make diagnostics easier. i will however double check again just in case.

should i try swapping out the egr valve? i have not done so yet. again, thanks for the responses and keep em coming.
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post #7 of (permalink) Old 08-20-2003, 09:13 PM
 
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Re: bad idle and miss after engine warms

When was the last time the valves were adjusted? They tend to tighten up over time. When the motor warms up, they expand, this pops the valve open slightly. Just a thought.
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post #8 of (permalink) Old 08-21-2003, 02:50 AM
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Re: bad idle and miss after engine warms

Have you checked you PCV valve?

I was having a similar problem recently with my stock carb, and I'm sure that was what was causing it.

While I was putting on a weber carb I tested the PCV valve according to the FSM, and it was toast. That would explain the problem, and if you read the factory service manual, it lists all sorts of problems like hard starting and bad/no idle under symptoms of a bad PCV.

I took it off and plugged the manifold when I put on the weber, and at the moment I just vent into the intake above the carb.
When I get around to it I'll make breather bottle / catch can, and vent to that so my motor doesn't have to put up with the crappy low octane blowby gas.

You should get hold of a vacuum gauge and check the intake manifold vacuum to see if you do have a leak or bad PCV. I've tried the carb cleaner technique and it doens't always work.

Hope that helps


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post #9 of (permalink) Old 08-21-2003, 01:20 PM
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Re: bad idle and miss after engine warms

I've pluged my pcv before (with my finger) and it almost stalled the engine?! It pulled a heck of a vacuum though, is this good/bad??

Can I plug the pcv? I know it's a good thing that the engine has a slight vacuum inside, so the oil does not blow out the seals.
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post #10 of (permalink) Old 08-21-2003, 05:37 PM Thread Starter
 
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Re: bad idle and miss *PROBLEM FOUND*

well the problem has been found. the wires running to the stock carb electronics that are supposed to be "hot" when the ignition becomes energized are no longer "hot".

dieseltech came over and diagnosed teh problem in about 15 minutes, and i have spent two days and still couldn't figure it out.

well to test it out, we temporarily ran hot wires straight from the battery to the wires that are supposed to become hot when the ignition key is turned. amazingly the idle smoothed out and the horrible miss disappeared. now i just have to figure out a way to make a permanent fix for it.

the problem was since there was no voltage getting to the various sensors or whatnot, the feedback wires that go to the carb ecm were sending no signals.

thanks to everyone that gave me ideas, i am just glad this gremlin has been found.

[img]images/graemlins/40BEER.gif[/img]
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