1992 misfiring badly at autocross
07-07-2014, 07:18 AM
#1
Racer
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Location: Peabody MA
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1992 misfiring badly at autocross
The problem:
It gets progressively worse as the car gets warmer. At operating temperature, just driving around normally, it'll buck a little bit at very low rpm at full throttle but be fine otherwise. At autocross, it was getting severe to the point where I couldn't race anymore, I had to let the car cool down completely before I could drive it home.
It appears to be temperature related. I'm not sure if it has something to do with entering closed loop, but the car still has the issue at WOT and partial throttle.
Codes:
I cleared the codes and drove the car fairly hard for 20 minutes to get it to act up. I got codes H21 (TPS voltage high) and H64 (right bank oxygen sensor detected lean conditions).
Solution:
I ohmed the old Multec injectors while cool, they all read about 16.6 ohms. When hot, they were all about 16.1. I'm not exactly sure what to check next, other than TPS voltage. Would the TPS voltage get progressively worse as the car became warmer?
I believe that heat is causing something electronic to fail OR I'm having some sort of fuel issue... I really hope it's not the Opti, which was replaced 45k miles ago. Car is daily driven and raced hard a few times per month at autocross and hill climbs. Any help is appreciated as I have a race this weekend, thanks in advance.
It gets progressively worse as the car gets warmer. At operating temperature, just driving around normally, it'll buck a little bit at very low rpm at full throttle but be fine otherwise. At autocross, it was getting severe to the point where I couldn't race anymore, I had to let the car cool down completely before I could drive it home.
It appears to be temperature related. I'm not sure if it has something to do with entering closed loop, but the car still has the issue at WOT and partial throttle.
Codes:
I cleared the codes and drove the car fairly hard for 20 minutes to get it to act up. I got codes H21 (TPS voltage high) and H64 (right bank oxygen sensor detected lean conditions).
Solution:
I ohmed the old Multec injectors while cool, they all read about 16.6 ohms. When hot, they were all about 16.1. I'm not exactly sure what to check next, other than TPS voltage. Would the TPS voltage get progressively worse as the car became warmer?
I believe that heat is causing something electronic to fail OR I'm having some sort of fuel issue... I really hope it's not the Opti, which was replaced 45k miles ago. Car is daily driven and raced hard a few times per month at autocross and hill climbs. Any help is appreciated as I have a race this weekend, thanks in advance.
07-07-2014, 10:35 AM
#2
Team Owner
Pro Mechanic
When my '92 did those symptoms, it was the Opti failing. Look at your tach when the symptom is happening....does the needle go crazy/bounce around/not follow engine RPM?
07-08-2014, 12:21 AM
#4
Team Owner
Pro Mechanic
Tach gets it's signal from the dist....so if stable/accurate, that is a good indicator. My opti went 150k, so...
Can you put a scan tool on it?
Can you put a scan tool on it?
06-09-2016, 12:55 PM
#6
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Location: Naugatuck CT
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My 92 LT1 had this symptom real bad this morning and I had to nurse it home 20 miles. the tach needle bounced randomly and I had frequent misfires. Up till now, the misfires would be rare and isolated to one or two per trip - especially when hot. Is it safe to presume that I need to replace the opti? I think it is original and we have 90,000 miles now.
06-09-2016, 05:21 PM
#8
or the coil or just your o2s. 