Intermittant rough idle
10-27-2011, 07:09 PM
#1
Intermittant rough idle
Hi guys,
Owned my 91 Z since 93. American Stainless headers no cats but thats about the only mod to the drivetriain.
For several years the car has had an intermittant very rough idle,
so rough if you dont blip the gas it will quit running. At mid to heavy throttle (secondaries come on) roughness goes away all is smooth. Generally speaking, but not always, the problem occus when engine is hot, but less frequently does occur when it is cold.
I have changed many parts over the years searching for the cure. Off the top of my head: both fuel pumps, both O2 sensors twice, fuel filter, both coils vacuume lines under the plenum, plugs, new SP wires, new Accel primary injectors (Ohm check numbers below), TPS sensor, IAC sensor twice and probably a few other things I have forgotten.
Not one of these changes has had any effect on the intermmitant rough
idle. Very difficult to diagnose b/c sometimes it will run fine for 1-2 hours and then fall apart at low throttle settings (secondaries closed).
Now for some clues. 1. It always runs perfect when the secondaries pop open and at one other time - when you turn the key off then restart it always runs perfect for the first 3-4 seconds. If those are both Open Loop, does that suggest a problem with the O2 system that I have not found yet?
Clue 2: I ran a resistance check on the injectors today. I ran the car for almost an hour and then did the primaries first (engine in full heat soak) and then the secondaries (not quite as hot due to elapsed time).
Results: Accels installed in primaries in 2007:
1- 16.1 2- 16.2 3- 16.2 4- 16.2 5- 16.0 6- 16.1 7-15.9 8- 16.0
Original FIs in secondaries as follows:
1- 13.4 2- 6.1 3- 10.9 4- 13.2 5- 11.1 6- 13.2 7- 13.2 8- 13.2
Remembers I put in the Accels in 2007 chasing this same problem and that the car runs perfectly when the secondaries come to life. The primaries test near perfect (I think) and secondaries not so good, but car idles like crap when hot (sometimes). Wouls a bad secondary FI or two affect idle somehow?
Clue 3. I have noticed the instrument cluster lighting flickering pretty much all the time at idle now, even when the car is idling good. These are the back lights for speedometer, radio etc. Could a bad ground be effecting all this?
Thanks for any input. I have about come to the end of my rope with this thing so any help appreciated. Sorry for the long post.
Regards
Owned my 91 Z since 93. American Stainless headers no cats but thats about the only mod to the drivetriain.
For several years the car has had an intermittant very rough idle,
so rough if you dont blip the gas it will quit running. At mid to heavy throttle (secondaries come on) roughness goes away all is smooth. Generally speaking, but not always, the problem occus when engine is hot, but less frequently does occur when it is cold.
I have changed many parts over the years searching for the cure. Off the top of my head: both fuel pumps, both O2 sensors twice, fuel filter, both coils vacuume lines under the plenum, plugs, new SP wires, new Accel primary injectors (Ohm check numbers below), TPS sensor, IAC sensor twice and probably a few other things I have forgotten.
Not one of these changes has had any effect on the intermmitant rough
idle. Very difficult to diagnose b/c sometimes it will run fine for 1-2 hours and then fall apart at low throttle settings (secondaries closed).
Now for some clues. 1. It always runs perfect when the secondaries pop open and at one other time - when you turn the key off then restart it always runs perfect for the first 3-4 seconds. If those are both Open Loop, does that suggest a problem with the O2 system that I have not found yet?
Clue 2: I ran a resistance check on the injectors today. I ran the car for almost an hour and then did the primaries first (engine in full heat soak) and then the secondaries (not quite as hot due to elapsed time).
Results: Accels installed in primaries in 2007:
1- 16.1 2- 16.2 3- 16.2 4- 16.2 5- 16.0 6- 16.1 7-15.9 8- 16.0
Original FIs in secondaries as follows:
1- 13.4 2- 6.1 3- 10.9 4- 13.2 5- 11.1 6- 13.2 7- 13.2 8- 13.2
Remembers I put in the Accels in 2007 chasing this same problem and that the car runs perfectly when the secondaries come to life. The primaries test near perfect (I think) and secondaries not so good, but car idles like crap when hot (sometimes). Wouls a bad secondary FI or two affect idle somehow?
Clue 3. I have noticed the instrument cluster lighting flickering pretty much all the time at idle now, even when the car is idling good. These are the back lights for speedometer, radio etc. Could a bad ground be effecting all this?
Thanks for any input. I have about come to the end of my rope with this thing so any help appreciated. Sorry for the long post.
Regards
10-27-2011, 07:18 PM
#2
NCM Lifetime # 982
Your secondary injectors need to be changed.
The flickering lights check the battery and grounds. If they are good it's either a bad diode in the alternator or a BCM problem.
The flickering lights check the battery and grounds. If they are good it's either a bad diode in the alternator or a BCM problem.
Last edited by FU; 10-27-2011 at 07:20 PM.
10-27-2011, 09:21 PM
#3
Safety Car
Have you checked the battery voltage? These cars will run like crap if the battery isn't up to par. The flickering dash lights are probably caused by a bad diode in the alternator. I just had to have mine rebuilt due to the same symptom.
Like mentioned bdfore , check your grounds first.
Like mentioned bdfore , check your grounds first.
10-28-2011, 09:06 AM
#4
Melting Slicks
While testing the resistance of the fuel injectors did you back probe the yellow ECM plug with your volt meter?
I too had a rough idle that would come and go, seemed to be heat related and then sometimes not.
No clear pattern to the failure to ever get a solid diagnosis.
Took me much longer than I'd like to admit to finally figure out that I had stuck my volt meter probe into the holes of the ECM socket and had stretched out the female socket so bad that the male pins of the ECM only made intermittent contact.
I replaced all the female pins in the plug and my problems went away.
And do replace the 2* injectors.
#2 is definitely shot.
Good luck.
TomC
'Crabs
I too had a rough idle that would come and go, seemed to be heat related and then sometimes not.
No clear pattern to the failure to ever get a solid diagnosis.
Took me much longer than I'd like to admit to finally figure out that I had stuck my volt meter probe into the holes of the ECM socket and had stretched out the female socket so bad that the male pins of the ECM only made intermittent contact.
I replaced all the female pins in the plug and my problems went away.
And do replace the 2* injectors.
#2 is definitely shot.
Good luck.
TomC
'Crabs
10-28-2011, 06:50 PM
#5
Thanks for the replys.
This battery is not new but the car has been through several batteries during the course of this issue. That might be the fix for the dash lights
but I doubt it will help with the rough idle.
I realize I need to replace the secondary injectors. The issue here is not fixing the secondary injectors or the flickering instrument lights.
The issue here is "Will fixing those things fix my intermitant rough ide?"
Replacing the secondaries is something I can and will do. But I am
not spending another penny on this car unless it relates directly to troubleshooting this idle issue. Can bad secondaries affect idle? Logic
based on my limited knowlege of this car says that if there is an idle issue caused by bad FIs it would show up in the primaries. They tested bad in 2007 and so I replaced them thinking that would solve the problem. Actually I took all 16 injectors to an injector shop, had them all flowed and tested and asked them to pick the best 8 from the bunch. I put Accels in the primaries and took the "best" 8 and put them in the secondaries. If someone can tell me that changing the secondaries can affect idle then that will certainly be my next step.
As to my scattergun approach over the years, each item was replaced either because it was time (plugs for instance) or because I read about or talked to someone who had fixed an idle problem that way. Most of the things I listed (except the FIs) were cheap/easy to do so it was worth a shot. Over the years I have checked fuel preassure, spark at the plug each cylinder (all firing), vacuum leaks, and other basics and all checked good. I have also run through the ALDL codes in the past and gotten nowhere, although not lately so that is worth a recheck. I have also borrowed a friends 91 chip and swapped it in place of my chip. No help.
The car has been diagnosed in person by both Marc Haibeck and Gordon Killebrew, albeit briefly. Haibeck was at a car show at the Bowling Green drag strip. A mutual friend introduced us. I described my issues and he did a FI test on the spot. Gordon K had a free diagnostic tent set up at the Corevtte Museum a few years back. He also did the same test. Both had the same suggestion: Replace the primary injectors. I did so to no avail. Marc knows his stuff for sure but he is expensive and with 3 in college this year professional help is pretty much out of the question until I have exhausted other avenues (and thus my postings here)
I will also post on the ZR1 Registry site. I have been a member there since 1994 but have used the Z less and less over the years due to this annoying problem.
I am going to research which grounds might effect ignition, fuel preassure, ECM etc or maybe I will just check them all. Some look like they are on the back side of the motor and so hard to get at but I'll see what I can do. I also seem to recall having already done this years ago but can always recheck.
I still think the biggest clue I listed is the fact that the idle problem is NEVER present at start up, even on a hot restart. It can be in the throws of idling so badly that it will stall if I dont blip the throttle. Yet if I turn the key off, then re-start it runs smooth as silk during the initial start RPM surge, and then runs like crap immediately after. Why is that? What is different during the start sequence that allows it to run well? Open vs closed loop? Do all 16 injectors activate during the start sequence? Both fuel pumps? Different grounds? There is a clue there just have not figured it out yet.
Thanks for the replies.
This battery is not new but the car has been through several batteries during the course of this issue. That might be the fix for the dash lights
but I doubt it will help with the rough idle.
I realize I need to replace the secondary injectors. The issue here is not fixing the secondary injectors or the flickering instrument lights.
The issue here is "Will fixing those things fix my intermitant rough ide?"
Replacing the secondaries is something I can and will do. But I am
not spending another penny on this car unless it relates directly to troubleshooting this idle issue. Can bad secondaries affect idle? Logic
based on my limited knowlege of this car says that if there is an idle issue caused by bad FIs it would show up in the primaries. They tested bad in 2007 and so I replaced them thinking that would solve the problem. Actually I took all 16 injectors to an injector shop, had them all flowed and tested and asked them to pick the best 8 from the bunch. I put Accels in the primaries and took the "best" 8 and put them in the secondaries. If someone can tell me that changing the secondaries can affect idle then that will certainly be my next step.
As to my scattergun approach over the years, each item was replaced either because it was time (plugs for instance) or because I read about or talked to someone who had fixed an idle problem that way. Most of the things I listed (except the FIs) were cheap/easy to do so it was worth a shot. Over the years I have checked fuel preassure, spark at the plug each cylinder (all firing), vacuum leaks, and other basics and all checked good. I have also run through the ALDL codes in the past and gotten nowhere, although not lately so that is worth a recheck. I have also borrowed a friends 91 chip and swapped it in place of my chip. No help.
The car has been diagnosed in person by both Marc Haibeck and Gordon Killebrew, albeit briefly. Haibeck was at a car show at the Bowling Green drag strip. A mutual friend introduced us. I described my issues and he did a FI test on the spot. Gordon K had a free diagnostic tent set up at the Corevtte Museum a few years back. He also did the same test. Both had the same suggestion: Replace the primary injectors. I did so to no avail. Marc knows his stuff for sure but he is expensive and with 3 in college this year professional help is pretty much out of the question until I have exhausted other avenues (and thus my postings here)
I will also post on the ZR1 Registry site. I have been a member there since 1994 but have used the Z less and less over the years due to this annoying problem.
I am going to research which grounds might effect ignition, fuel preassure, ECM etc or maybe I will just check them all. Some look like they are on the back side of the motor and so hard to get at but I'll see what I can do. I also seem to recall having already done this years ago but can always recheck.
I still think the biggest clue I listed is the fact that the idle problem is NEVER present at start up, even on a hot restart. It can be in the throws of idling so badly that it will stall if I dont blip the throttle. Yet if I turn the key off, then re-start it runs smooth as silk during the initial start RPM surge, and then runs like crap immediately after. Why is that? What is different during the start sequence that allows it to run well? Open vs closed loop? Do all 16 injectors activate during the start sequence? Both fuel pumps? Different grounds? There is a clue there just have not figured it out yet.
Thanks for the replies.
10-29-2011, 08:45 AM
#6
Le Mans Master
Member Since: Oct 2004
Location: South-central Missouri
Posts: 6,314
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Cutting to the chase, electronic (feedback) loop systems require good steady voltage and ground references. They often determine the state of a sensor (for example) by the differential between the sensor signal and the reference voltage, and react accordingly.
Illustration: The height of the deck of a boat is dropping in relation to the pier. Q: "Is the tide going out or is the boat sinking...or both?" One set of circumstances are present IF the pier height is fixed. But, another set of circumstances exist if it is a floating pier. Get my "drift"? In short, it IS important to eliminate issues as they present themselves in order to clear the deck so remaining issues are more in the open - not obscured by other goings on. (This is especially true where feedback circuits are involved
)I still think the biggest clue I listed is the fact that the idle problem is NEVER present at start up, even on a hot restart. It can be in the throws of idling so badly that it will stall if I dont blip the throttle. Yet if I turn the key off, then re-start it runs smooth as silk during the initial start RPM surge, and then runs like crap immediately after. Why is that? What is different during the start sequence that allows it to run well? Open vs closed loop? Do all 16 injectors activate during the start sequence? Both fuel pumps? Different grounds? There is a clue there just have not figured it out yet.
If it does, then we can set aside the DIS (I didn't say eliminate...just yet), eliminate coils and SP wires and SPs themselves.
Now the focus is on the BLMs, the O2s, MAP, injector dwell time. If you had access to a wide-band O2 sensor, it would be interesting to see the "before and after" readings as the idle drops from normal to a bad miss. (From what you've told us so far, I'm wondering if it is related to CLOSED loop operation, and if so, is it a lean situation? Did we ever determine anything from reading the plugs? Or, is there just one/two cylinders affected or does it seem to be more random, with regard to the misfiring?)
I am going to research which grounds might effect ignition, fuel preassure, ECM etc or maybe I will just check them all. Some look like they are on the back side of the motor and so hard to get at but I'll see what I can do. I also seem to recall having already done this years ago but can always recheck.
Nuff for now. But, I'm intrigued... Some people like crossword puzzles. I enjoy ferreting out electrical issues. Sick, I know, but what can I say?
I must say too that although I can fall back on decades of experience in troubleshooting many kinds of electronic "stuff", I'm depending on those dearly learned, universal process more than intimate knowledge gained by those with considerable experience with the ZR-1/LT5 electronics in particular! So take it for what it's worth, and hence my suggestion to take this over to the Registry where ppl like Marc that have both the process and the experience to guide their thinking...would be worth considering.Wish you lived closer. Finding this problem sounds like fun!! (Tollja I was a sick bastard...
) Besides...Long as this has plagued you, I hate to think of how frustrating it must seem by now. Many would have thrown in the towel long ago!! So, I really hope the Brotherhood can come to a resolution with you!P.
10-29-2011, 11:32 AM
#7
Melting Slicks
Yellow91, seriously consider my suggestion above.
If there's *ANY* chance that the ECM plug pins have been probed by your or any one else, this will cause symptoms *EXACTLY* like what you describe.
I spent about 3 years trying to figure this little gremlin out, and spent more money on new parts than I'd like to admit.
It was so frustrating, you just can't believe. (well, maybe you can)
I was at the point of putting it on eBay and let the next owner figure it out.
Beg, borrow or buy the crimp tool and extraction tool, the pins will only cost you $20 or so.
If you were close to me I'd invite myself over and change all the pins myself.
TomC
'Crabs
10-29-2011, 01:08 PM
#8
Safety Car
Your older secondary injectors, while not active at idle, could simply be dripping.
One of the primary injectors, while electrically good, may be clogged and have a mediocre spray pattern.
The flickering dash light- mine has that- I think it's a voltage regulation problem, in part, but if you can maintain a steady idle- it's a little better off in general for alternator output. Vacuum leaks and PVC flow can contribute to a little high idle or an IAC target that is zero'd out and can no longer adjust idle targets lower.
Like was mentioned, it could be more than one cause and effect. I did all 16 injectors (new) when the Lucas ones were on promotion for 5 bills. it idled so much better after that. The plugs and vacuum leaks were all addressed with the plenum pull too. I would get a tech1 type of scanner and realtime monitor various sensors. The O2 sensor values bear looking at right to left as well as BLM's fuel trims etc.
I have a bad feeling about your injectors. Also do the fundamentals like compression checking and fouled plug inspection.
One of the primary injectors, while electrically good, may be clogged and have a mediocre spray pattern.
The flickering dash light- mine has that- I think it's a voltage regulation problem, in part, but if you can maintain a steady idle- it's a little better off in general for alternator output. Vacuum leaks and PVC flow can contribute to a little high idle or an IAC target that is zero'd out and can no longer adjust idle targets lower.
Like was mentioned, it could be more than one cause and effect. I did all 16 injectors (new) when the Lucas ones were on promotion for 5 bills. it idled so much better after that. The plugs and vacuum leaks were all addressed with the plenum pull too. I would get a tech1 type of scanner and realtime monitor various sensors. The O2 sensor values bear looking at right to left as well as BLM's fuel trims etc.
I have a bad feeling about your injectors. Also do the fundamentals like compression checking and fouled plug inspection.
10-29-2011, 05:48 PM
#9
Yellow91, seriously consider my suggestion above.
If there's *ANY* chance that the ECM plug pins have been probed by your or any one else, this will cause symptoms *EXACTLY* like what you describe.
I spent about 3 years trying to figure this little gremlin out, and spent more money on new parts than I'd like to admit.
It was so frustrating, you just can't believe. (well, maybe you can)
I was at the point of putting it on eBay and let the next owner figure it out.
Beg, borrow or buy the crimp tool and extraction tool, the pins will only cost you $20 or so.
If you were close to me I'd invite myself over and change all the pins myself.
TomC
'Crabs
If there's *ANY* chance that the ECM plug pins have been probed by your or any one else, this will cause symptoms *EXACTLY* like what you describe.
I spent about 3 years trying to figure this little gremlin out, and spent more money on new parts than I'd like to admit.
It was so frustrating, you just can't believe. (well, maybe you can)
I was at the point of putting it on eBay and let the next owner figure it out.
Beg, borrow or buy the crimp tool and extraction tool, the pins will only cost you $20 or so.
If you were close to me I'd invite myself over and change all the pins myself.
TomC
'Crabs
I would say initially I don't suspect my plugs to be bad because the only people to ever probe it are Haibeck, Killebrew and myself, and all of those were in search of the current problem. I have owned the car since it was a year old and am pretty sure noone was "probing" before me
. However, the connection could be bad for other reasons.I will wiggle it next time my idle falls apart and see if that helps.
Thanks
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Corvette Cool Guy (08-22-2019)
10-29-2011, 05:54 PM
#10
Your older secondary injectors, while not active at idle, could simply be dripping.
One of the primary injectors, while electrically good, may be clogged and have a mediocre spray pattern.
The flickering dash light- mine has that- I think it's a voltage regulation problem, in part, but if you can maintain a steady idle- it's a little better off in general for alternator output. Vacuum leaks and PVC flow can contribute to a little high idle or an IAC target that is zero'd out and can no longer adjust idle targets lower.
Like was mentioned, it could be more than one cause and effect. I did all 16 injectors (new) when the Lucas ones were on promotion for 5 bills. it idled so much better after that. The plugs and vacuum leaks were all addressed with the plenum pull too. I would get a tech1 type of scanner and realtime monitor various sensors. The O2 sensor values bear looking at right to left as well as BLM's fuel trims etc.
I have a bad feeling about your injectors. Also do the fundamentals like compression checking and fouled plug inspection.
One of the primary injectors, while electrically good, may be clogged and have a mediocre spray pattern.
The flickering dash light- mine has that- I think it's a voltage regulation problem, in part, but if you can maintain a steady idle- it's a little better off in general for alternator output. Vacuum leaks and PVC flow can contribute to a little high idle or an IAC target that is zero'd out and can no longer adjust idle targets lower.
Like was mentioned, it could be more than one cause and effect. I did all 16 injectors (new) when the Lucas ones were on promotion for 5 bills. it idled so much better after that. The plugs and vacuum leaks were all addressed with the plenum pull too. I would get a tech1 type of scanner and realtime monitor various sensors. The O2 sensor values bear looking at right to left as well as BLM's fuel trims etc.
I have a bad feeling about your injectors. Also do the fundamentals like compression checking and fouled plug inspection.
A clogged injector would be clogged all the time, not intermittant, right?
I have done fouled plugs and compression. All good there but again they would be fouled and compression bad all the time, not sometimes.
I will look for a used Tech1 on ebay.
Got to go. I am in New Orleans and its Saturday night!
Thanks
10-29-2011, 05:56 PM
#11
Yellow91, seriously consider my suggestion above.
If there's *ANY* chance that the ECM plug pins have been probed by your or any one else, this will cause symptoms *EXACTLY* like what you describe.
I spent about 3 years trying to figure this little gremlin out, and spent more money on new parts than I'd like to admit.
It was so frustrating, you just can't believe. (well, maybe you can)
I was at the point of putting it on eBay and let the next owner figure it out.
Beg, borrow or buy the crimp tool and extraction tool, the pins will only cost you $20 or so.
If you were close to me I'd invite myself over and change all the pins myself.
TomC
'Crabs
If there's *ANY* chance that the ECM plug pins have been probed by your or any one else, this will cause symptoms *EXACTLY* like what you describe.
I spent about 3 years trying to figure this little gremlin out, and spent more money on new parts than I'd like to admit.
It was so frustrating, you just can't believe. (well, maybe you can)
I was at the point of putting it on eBay and let the next owner figure it out.
Beg, borrow or buy the crimp tool and extraction tool, the pins will only cost you $20 or so.
If you were close to me I'd invite myself over and change all the pins myself.
TomC
'Crabs
Later
08-08-2019, 05:49 PM
#12
I have had this issue many, many years ago with my 85, Problem was the ECM - dealer fixed after grilled them. Car stayed with them for days so they could throw parts at it.
I do believe there was a service bulletin issued for the ecm (or maybe prom). for 85.
Other suspects as others will probably point out. MAF. Unplug the MAF and see if it run better. MAF burn off relay - unique to 85 could cause symptoms as well. Coolant temp sensor. You mention grounds, Could be that too.
Given the mix and severity of the problems, I don't think it is going to be the typical fuel, vacuum stuff.
Good luck and let us know how it works out.
I do believe there was a service bulletin issued for the ecm (or maybe prom). for 85.
Other suspects as others will probably point out. MAF. Unplug the MAF and see if it run better. MAF burn off relay - unique to 85 could cause symptoms as well. Coolant temp sensor. You mention grounds, Could be that too.
Given the mix and severity of the problems, I don't think it is going to be the typical fuel, vacuum stuff.
Good luck and let us know how it works out.
08-08-2019, 07:33 PM
#13
Le Mans Master
The #2 secondary injector looks to be the most out of range with the rest of the secondaries, and even they are off amongst one another. I believe Marc’s guide on back probing connector A for these readouts mentioned the injectors shouldn’t vary from one another, cold or hot by +\- .01 for resistance.
I had the primary on #8 act up once saturated entirely with heat. Before I settled on the injector issue, I attempted a 6th gear pull to test out if my issue was a coil, the car bucked quite a bit and refused to accelerate while the dash flickered just as you are describing.
it could also be a combo of issues. For acceleration before my injectors started acting up, I had an issue where the car would accelerate fine but coasting down to slow to a stop would cause the car to catch itself just before stalling or stall. Turned out someone had replaced the MAP sensor vac line with some flimsy rubber hose that got soaked with oil and collapsed when the throttle blades closed shut coming off the gas to coast down.
I had the primary on #8 act up once saturated entirely with heat. Before I settled on the injector issue, I attempted a 6th gear pull to test out if my issue was a coil, the car bucked quite a bit and refused to accelerate while the dash flickered just as you are describing.
it could also be a combo of issues. For acceleration before my injectors started acting up, I had an issue where the car would accelerate fine but coasting down to slow to a stop would cause the car to catch itself just before stalling or stall. Turned out someone had replaced the MAP sensor vac line with some flimsy rubber hose that got soaked with oil and collapsed when the throttle blades closed shut coming off the gas to coast down.
08-09-2019, 02:43 PM
#15
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Well I sure hope the OP got his issues resolved by now .....
09-03-2019, 08:07 AM
#16
Le Mans Master
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Location: South-central Missouri
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Yes, well in spite of the OP's thread being so old, the issue comes up on a regular basis still - especially with new ZR-1 owners. And, checking the O2s (when they're HOT, by the way) is still as valid as ever. You might say this is one for "the file", no?
