91 hard start when hot no codes
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From: jax fl
91 hard start when hot no codes
My 91 auto is hard starting if at all when hot. Runs/starts fine cold when it gets hot it stumbles under acceleration and is hard to start.
Originally displayed a coolant temp sensor code and I replaced that but I continue to have the hard start problem. It is not displaying any codes other than the C12 (ok) code.
Hot it will not start at all until it cools down with no throttle or partial throttle. It will fire and run with wide open throttle, it will return to idle and run but when put in drive and you accelerate it dies. After it cools it will fire and run ok until it heats up.
My guess is throttle position sensor or MAP sensor. Any ideas? I will test the tps tomorrow.
Originally displayed a coolant temp sensor code and I replaced that but I continue to have the hard start problem. It is not displaying any codes other than the C12 (ok) code.
Hot it will not start at all until it cools down with no throttle or partial throttle. It will fire and run with wide open throttle, it will return to idle and run but when put in drive and you accelerate it dies. After it cools it will fire and run ok until it heats up.
My guess is throttle position sensor or MAP sensor. Any ideas? I will test the tps tomorrow.
Team Owner
Joined: Jan 2009
Posts: 73,568
Likes: 33
From: Somewhere in Mo
St. Jude Donor '09-'10, '14
Catalytic converter maybe. I'll look in my FSM and come back if I find anything
Seems someone else had this problem recently and it was the ECM maybe. I think someone else had a bad coil. But it may be a bad connection at the sensor as well.
Ok I checked my book. I have a 90 L98 so they should be the same car.
If you threw a code 14 for the Coolant temp sensor the book says there are two reasons. Bad sensor or bad ecm.
But the books don't alway tell the truth. I would do a fuel pressure test just to rule that out, along with the ohm test that Agent 86 is suggesting below.
If you do a search you may find a thread that was discussed here a month or so back. But this search engine is not the most user friendly so good luck on that.
Out of curiosity was it doing this before the sensor exchange?
Seems someone else had this problem recently and it was the ECM maybe. I think someone else had a bad coil. But it may be a bad connection at the sensor as well.
Ok I checked my book. I have a 90 L98 so they should be the same car.
If you threw a code 14 for the Coolant temp sensor the book says there are two reasons. Bad sensor or bad ecm.
But the books don't alway tell the truth. I would do a fuel pressure test just to rule that out, along with the ohm test that Agent 86 is suggesting below.
If you do a search you may find a thread that was discussed here a month or so back. But this search engine is not the most user friendly so good luck on that.
Out of curiosity was it doing this before the sensor exchange?
Last edited by RetiredSFC 97; Jan 18, 2010 at 08:35 PM.
Thread Starter
Instructor
Joined: Jul 2002
Posts: 172
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From: jax fl
Catalytic converter maybe. I'll look in my FSM and come back if I find anything
Seems someone else had this problem recently and it was the ECM maybe. I think someone else had a bad coil. But it may be a bad connection at the sensor as well.
Ok I checked my book. I have a 90 L98 so they should be the same car.
If you threw a code 14 for the Coolant temp sensor the book says there are two reasons. Bad sensor or bad ecm.
But the books don't alway tell the truth. I would do a fuel pressure test just to rule that out, along with the ohm test that Agent 86 is suggesting below.
If you do a search you may find a thread that was discussed here a month or so back. But this search engine is not the most user friendly so good luck on that.
Out of curiosity was it doing this before the sensor exchange?
Seems someone else had this problem recently and it was the ECM maybe. I think someone else had a bad coil. But it may be a bad connection at the sensor as well.
Ok I checked my book. I have a 90 L98 so they should be the same car.
If you threw a code 14 for the Coolant temp sensor the book says there are two reasons. Bad sensor or bad ecm.
But the books don't alway tell the truth. I would do a fuel pressure test just to rule that out, along with the ohm test that Agent 86 is suggesting below.
If you do a search you may find a thread that was discussed here a month or so back. But this search engine is not the most user friendly so good luck on that.
Out of curiosity was it doing this before the sensor exchange?
It threw a 15(think that was it) code for a low temp fault on the CTS. I looked it up in the FSM when it did it.
Yes it did it before the sensor change, I was sure that was the problem but turns out I was wrong.
I did not do an official fuel pressure test but when it would not start it would had pressure at the test port on the fuel rails.
Yes, the search engine was not my friend on this one.
The FSM lists the TPS and MAP sensor as possible under hard start sceanrios.
Many thanks to everyone for the suggestions. One of those times I wish I had a tech 1 to scan it with.
Team Owner
Joined: Jan 2009
Posts: 73,568
Likes: 33
From: Somewhere in Mo
St. Jude Donor '09-'10, '14
when you said you replaced the temp sensor I thought it threw a 14 code, which is also the temp sensor and or ecm.
There are going to be a few things that cause this so you are going to have to go through each one to rule them out.
The injectors could be the culprit so you'll have to run a test on them as well.
I will look around the search engine today and see if I find anything, if I do I will send those threads to you.
There are going to be a few things that cause this so you are going to have to go through each one to rule them out.
The injectors could be the culprit so you'll have to run a test on them as well.
I will look around the search engine today and see if I find anything, if I do I will send those threads to you.
Team Owner
Joined: Jan 2009
Posts: 73,568
Likes: 33
From: Somewhere in Mo
St. Jude Donor '09-'10, '14
I'm going to throw a few threads at you to ponder on
http://forums.corvetteforum.com/c4-t...bonkers-2.html
http://forums.corvetteforum.com/c4-t...idle-cold.html
http://forums.corvetteforum.com/c4-s...r-warm-up.html
Here a some threads I found that may help. The last one talks about bad injectors.
here's another one
http://forums.corvetteforum.com/c4-t...-this-out.html
http://forums.corvetteforum.com/c4-t...bonkers-2.html
http://forums.corvetteforum.com/c4-t...idle-cold.html
http://forums.corvetteforum.com/c4-s...r-warm-up.html
Here a some threads I found that may help. The last one talks about bad injectors.
here's another one
http://forums.corvetteforum.com/c4-t...-this-out.html
Last edited by RetiredSFC 97; Jan 19, 2010 at 09:32 AM.
Thread Starter
Instructor
Joined: Jul 2002
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From: jax fl
I'm going to throw a few threads at you to ponder on
http://forums.corvetteforum.com/c4-t...bonkers-2.html
http://forums.corvetteforum.com/c4-t...idle-cold.html
http://forums.corvetteforum.com/c4-s...r-warm-up.html
Here a some threads I found that may help. The last one talks about bad injectors.
here's another one
http://forums.corvetteforum.com/c4-t...-this-out.html
http://forums.corvetteforum.com/c4-t...bonkers-2.html
http://forums.corvetteforum.com/c4-t...idle-cold.html
http://forums.corvetteforum.com/c4-s...r-warm-up.html
Here a some threads I found that may help. The last one talks about bad injectors.
here's another one
http://forums.corvetteforum.com/c4-t...-this-out.html
The scan tool shows the coolant temp reading as expected say at 150 then 160 then it drops to a ridiculous number like 18 then back up to 160. Very sporadic as it gets hotter. Not sure if it is throwing a code or not will have to check it.
My guess at this time is a bad ground on the wire to the cts or a bad wire/connection on the cts. The other thought is maybe I have a bad ecm.
I will post another update when I have time in the light on a warm day to look it over!
thanks to everyone for the suggestions.
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Thread Starter
Instructor
Joined: Jul 2002
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From: jax fl
Just wanted to post an update. I bought an Auto Xray 2000 scan tool to view live data... great deal for $90 off of Amazon.
The scan tool shows the coolant temp reading as expected say at 150 then 160 then it drops to a ridiculous number like 18 then back up to 160. Very sporadic as it gets hotter. Not sure if it is throwing a code or not will have to check it.
My guess at this time is a bad ground on the wire to the cts or a bad wire/connection on the cts. The other thought is maybe I have a bad ecm.
I will post another update when I have time in the light on a warm day to look it over!
thanks to everyone for the suggestions.
The scan tool shows the coolant temp reading as expected say at 150 then 160 then it drops to a ridiculous number like 18 then back up to 160. Very sporadic as it gets hotter. Not sure if it is throwing a code or not will have to check it.
My guess at this time is a bad ground on the wire to the cts or a bad wire/connection on the cts. The other thought is maybe I have a bad ecm.
I will post another update when I have time in the light on a warm day to look it over!
thanks to everyone for the suggestions.
