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1989 idle humbs and 1500rpm hesitation
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Author:  Karpov [ Wed Feb 28, 2018 8:16 am ]
Post subject:  Re: 1989 and hard cold start + other problems like transmiss

Tried new plug wires again. Nothing.

Iac was good too.

Cleaned maf also.


Now i but new plugs because old ones was fueled. I must try start pilot too

Author:  Karpov [ Wed Feb 28, 2018 12:30 pm ]
Post subject:  Re: 1989 and hard cold start + other problems like transmiss

Is this normal sparking in waste spark? Same things in every wire.

https://aijaa.com/B3XX2f

There is video for my start with strobo.

Author:  MKMike [ Thu Mar 01, 2018 3:16 pm ]
Post subject:  Re: 1989 and hard cold start + other problems like transmiss

That doesn't look like I would expect it to.
Assuming this is not a problem with your timing light, then it's not getting spark sometimes.
Since you said this happens on all wires, the problem is not a single bad coil and it is not likely that all coils are bad.

You'll have to figure out if that is from a problem with the ICM or the crankshaft position sensor.

The pages here show you how to test these:
http://easyautodiagnostics.com/gm/3.8L/ ... sor-test-1
http://troubleshootmyvehicle.com/gm/3.8 ... k-sensor-1

Author:  Karpov [ Thu Mar 01, 2018 5:56 pm ]
Post subject:  Re: 1989 and hard cold start + other problems like transmiss

Can crank sensor do intermitted spark? Its usually shuts spark off?

Same spark in every six wires. I did not regonized that at short start but longer start it appeared.

Maybe spark is also too weak under compression?


Maybe i just order new icm and coil. New crank sensor is on my garage because i ordered it just in case.

Outside -30 celcius so wire and anything else works wont be nice :)

Author:  Karpov [ Wed Mar 14, 2018 12:36 pm ]
Post subject:  Re: 1989 and hard cold start + other problems like transmiss

New icm and coil.

No start :(

I check later that spark is coming (new parts allready broken?)


What is next to check?

Author:  96 SSEi [ Wed Mar 14, 2018 1:54 pm ]
Post subject:  Re: 1989 and hard cold start + other problems like transmiss

crank position sensor - check it

Author:  Karpov [ Wed Mar 14, 2018 4:44 pm ]
Post subject:  Re: 1989 and hard cold start + other problems like transmiss

96 SSEi wrote:
crank position sensor - check it

No start guide said that if spark is coming, crank sensor is fine. And that meaned both signals. Was this guide rubbish?



Is there hint for set new sensor right? I remember that i get plastic tool with it (my ex buick 3800 in 2014) but now there was only sensor.

I ordered it about 2month ago and i have it.

Author:  96 SSEi [ Wed Mar 14, 2018 5:39 pm ]
Post subject:  Re: 1989 and hard cold start + other problems like transmiss

check the sensor for signals again

Author:  Karpov [ Thu Mar 15, 2018 5:23 am ]
Post subject:  Re: 1989 and hard cold start + other problems like transmiss

I did the multimeter dc test on 3x and 18x wires.

Both wires had 9volts. I had bad socket so i didnt turn crank full turn.

3x was 9v all time but i think i didnt turn engine enought to get it 0 point.

18x gived 9 to 0 when i turned engine even little.

Crank sensor plug off, it gived 9 volts both wires (i didnt rotated engine this time).


With sensor plug of and normal start, spark was gone.

Sensor plug on spark was on all cylinders, but intermitted like before.

Author:  Karpov [ Thu Mar 15, 2018 8:03 am ]
Post subject:  Re: 1989 and hard cold start + other problems like transmiss

I get right socket and i rotated engine many times.

Now 3x gived 9 to 0 on off depending crank position.

But why 9 volts if guide says 5-6?

Author:  Karpov [ Thu Mar 15, 2018 10:43 am ]
Post subject:  Re: 1989 and hard cold start + other problems like transmiss

Compression test was fine. I start engine without plugs anf injectors plugged off. It throwed fuel in firewall.



I did that a while, then i installed 100miles driven dry plugs.

It said hyrsk hyrsk couple times but no start. Same problem that has been whole time.

Author:  Karpov [ Thu Mar 15, 2018 12:10 pm ]
Post subject:  Re: 1989 and hard cold start + other problems like transmiss

Got it run. I think its coolant sensor.

Author:  Karpov [ Fri Mar 16, 2018 2:54 pm ]
Post subject:  Re: 1989 and hard cold start + other problems like transmiss

Is there some relearn or adjust process for iac?

Author:  96 SSEi [ Fri Mar 16, 2018 3:37 pm ]
Post subject:  Re: 1989 and hard cold start + other problems like transmiss

try starting with the old iac to see what happens

Author:  Karpov [ Fri Mar 16, 2018 3:48 pm ]
Post subject:  Re: 1989 and hard cold start + other problems like transmiss

I have old iac. I dont have another iac.

Car starts fine but stalls. When i start with gas pedal then it keeps idle but it humbs often than early.

And d on it pulls faster than before.


I think engine was full of fuel and when i taked plugs of and run it with start (injectors plugged of) fuel went out and new icm/coil worked.


But idle is not good.

Author:  Karpov [ Wed Mar 21, 2018 5:30 am ]
Post subject:  Re: 1989 and hard cold start + other problems like transmiss

Started good and immediatelly after 4 days pause.

Idle is high and D position it goes about 30mph without touching gas pedal :)

Vacuum leak?

Author:  Karpov [ Thu Mar 22, 2018 5:38 pm ]
Post subject:  Re: 1989 and hard cold start + other problems like transmiss

Is it normal that when i start warm/hot engine, rpm is 1500 about nano second and then drops 700rpm?

Author:  96 SSEi [ Fri Mar 23, 2018 6:36 am ]
Post subject:  Re: 1989 and hard cold start + other problems like transmiss

with high idle, I would check the iac and maf

Author:  Karpov [ Fri Mar 23, 2018 9:26 am ]
Post subject:  Re: 1989 and hard cold start + other problems like transmiss

So normal warm/hot engine starts example 700rpm and stays here? Not even nano second higher rpm?

Author:  Karpov [ Fri Mar 23, 2018 2:15 pm ]
Post subject:  Re: 1989 and hard cold start + other problems like transmiss

Hot engine idle humbs but if you drive and then go park its ok and steady.

1500rpm stumble is back too. Oh boy.

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