84 Crossfire Missing Once It Reaches Temp - Help Please
Thread Starter
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Joined: Oct 2014
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From: Brisbane
84 Crossfire Missing Once It Reaches Temp - Help Please
OK guys, looking for some help please. I've posted this stuff under a different thread title here, but haven't had any responses so have changed the title and see how we go.
I've got an 84 CFI and the car runs beautifully when started and driven cold. All good. Once it reaches temp, around 195, it starts misfiring and running rough. If I manually activate the fan, it cools to below that and eventually runs OK again.
As I understand it, the car is running in open loop whilst cold, but it seems once it reaches temp, it enters closed loop and that's when it runs rough.
So, I've changed the coolant temp sensor (CTS). I actually found that it had already been replaced, probably by the PO trying to find the same issue I'm dealing with. The car looks like it's got a new O2 sensor, but I can't be sure it's working properly. I've tried pulling codes once it runs rough, but no fault codes present.
I guess it could be either a faulty O2 sensor, a faulty CTS or faulty ECM. My plan is to try a process of elimination. I've replaced the CTS, next will be the O2 sensor, then the ECM. If anyone has any other suggestions for me to try, or has experienced and then remedied a similar issue, I'd be REALLY glad to hear from you.
Thank you
Darren
I've got an 84 CFI and the car runs beautifully when started and driven cold. All good. Once it reaches temp, around 195, it starts misfiring and running rough. If I manually activate the fan, it cools to below that and eventually runs OK again.
As I understand it, the car is running in open loop whilst cold, but it seems once it reaches temp, it enters closed loop and that's when it runs rough.
So, I've changed the coolant temp sensor (CTS). I actually found that it had already been replaced, probably by the PO trying to find the same issue I'm dealing with. The car looks like it's got a new O2 sensor, but I can't be sure it's working properly. I've tried pulling codes once it runs rough, but no fault codes present.
I guess it could be either a faulty O2 sensor, a faulty CTS or faulty ECM. My plan is to try a process of elimination. I've replaced the CTS, next will be the O2 sensor, then the ECM. If anyone has any other suggestions for me to try, or has experienced and then remedied a similar issue, I'd be REALLY glad to hear from you.
Thank you
Darren
Burning Brakes
Joined: Dec 2014
Posts: 1,038
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From: Pensacola Florida
FWIW my 89 had a similar issue. When cold it would run fine but once at operating temp it would have a irritating miss at cruise and idle. It however didn't miss a beat when I floored it. Turned out to be a couple of bad injectors in my case.
Rick
Rick
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Joined: Aug 2014
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Dont forget or over look the basics.
My 84 had a similar issue.
After some trial and error (no codes were present) I went back to basics and gave it an old fashioned tune up.
Plugs / wires / cap & rotor / etc.
I dont know which part was bad, but the problem went away, and hasnt come back.
My 84 had a similar issue.
After some trial and error (no codes were present) I went back to basics and gave it an old fashioned tune up.
Plugs / wires / cap & rotor / etc.
I dont know which part was bad, but the problem went away, and hasnt come back.
Team Owner
Joined: Sep 2003
Posts: 25,394
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In your other thread I believe you mentioned you did have the newer CTS but you could always check the function of the CTS using hot water and seeing that there's actually a change in resistance. Not done often but it's certainly an inexpensive check.
Does it flash the 12 indicating the ECM is actually functioning?
An early ECM problem would generally be evident using the "tap test" - if the ECM is hanging and accessible you could certainly try the "tap test" and see what might happen.
Here's a NAPA explanation but something other than the "finger tips" was used.
http://www.napaechlin.com/GM-Tap+Test/Content.aspx
You just need to start with very basic checks and work forward. Do you have the FSM?
Since the cross-fire in the C4 was a single year option you might do better using your favorite search engine and checking for cross-fire diagnostics all SBC Chevrolet.
There used to be some very dedicated people who owned C3 L83 cars and of course the F-body cars.
You mention the O2 only appears new. You need to confirm the fact that it's working.
*** I'd think a resolder of the ECM board locally would be a better choice than maybe a purchase taking into consideration - your location.
A search of the CF "crossfire diagnostics" in the C3 section yielded 45 threads, in the C4 section 56 threads - should be some very good reads for you.
Does it flash the 12 indicating the ECM is actually functioning?
An early ECM problem would generally be evident using the "tap test" - if the ECM is hanging and accessible you could certainly try the "tap test" and see what might happen.
Here's a NAPA explanation but something other than the "finger tips" was used.
http://www.napaechlin.com/GM-Tap+Test/Content.aspx
You just need to start with very basic checks and work forward. Do you have the FSM?
Since the cross-fire in the C4 was a single year option you might do better using your favorite search engine and checking for cross-fire diagnostics all SBC Chevrolet.
There used to be some very dedicated people who owned C3 L83 cars and of course the F-body cars.
You mention the O2 only appears new. You need to confirm the fact that it's working.
*** I'd think a resolder of the ECM board locally would be a better choice than maybe a purchase taking into consideration - your location.
A search of the CF "crossfire diagnostics" in the C3 section yielded 45 threads, in the C4 section 56 threads - should be some very good reads for you.
Last edited by WVZR-1; Jul 14, 2015 at 10:15 AM.
Thread Starter
Advanced
Joined: Oct 2014
Posts: 74
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From: Brisbane
Thank you
Thanks guys, some very good suggestions there. I'll start with checking the plug leads for arching. Then I'll do the tune up stuff (plugs, leads, cap and rotor). Then I'll look into the other stuff. Yes, it does flash the 12 when in test mode, and yes I have an FSM.
I genuinely appreciate the help and it gives me a way forward. I might be back shortly looking for advice on how to test the CTS and O2 sensor if I google doesn't help and I'll certainly get back and report progress.
Thanks again,
Darren
I genuinely appreciate the help and it gives me a way forward. I might be back shortly looking for advice on how to test the CTS and O2 sensor if I google doesn't help and I'll certainly get back and report progress.
Thanks again,
Darren
Last edited by 70chev; Jul 14, 2015 at 10:56 PM.
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Melting Slicks
Joined: Dec 2009
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Here's a coolant temp sensor resistance chart. With the engine 100% cold it should read close to the outside temp. You'll need an ohm meter.
When it's up to temp measure it again, just so you know the coolant temp will spike up some when you shut it off b/c the flow stopped.
When it's up to temp measure it again, just so you know the coolant temp will spike up some when you shut it off b/c the flow stopped.
Thread Starter
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Joined: Oct 2014
Posts: 74
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From: Brisbane
Thanks Ex. So do I use the two prongs of my ohm meter on the two prongs of the CTS fitting, or do I need to place one of the ohm meter prongs on the body of the CTS? And that's with it still fitted to the car right?
Thanks again.
Darren
Thanks again.
Darren