bad gasoline? (not!)
- Thread starter JD1964
- Start date
- Status
Vacuum line. V-A-C-U-U-M.
Please explain how a line under vacuum can expand to fit loosely on a fitting. 🤨
opti spark (booh on GM) haha
When it starts acting up check the spark at each cylinder with a timing light to be sure it's consistent.
You mentioned a possible valve train issue, but consistent vacuum - if you're vacuum is rock steady, then the valvetrain noise is most likely a symptom and not the cause of your issue. On the other hand, if the vacuum becomes unsteady and the valvetrain issue develops at the same time as the running issue, then I'd dive into that.
Good Luck (my money is on the opti spark, sadly)
A couple more things to check...
Is the EGR system still intact? A piece of carbon holding the pintle open will dilute the idle mixture but be less pronounced above idle.
I saw plenty of those Multec injectors fail. Didn't always cause a dead miss. Sometimes just an unsteady idle and a stumble just beyond. Usually an ohm test of each injector would point out the bad one.
Is the EGR system still intact? A piece of carbon holding the pintle open will dilute the idle mixture but be less pronounced above idle.
I saw plenty of those Multec injectors fail. Didn't always cause a dead miss. Sometimes just an unsteady idle and a stumble just beyond. Usually an ohm test of each injector would point out the bad one.
Thanks for all the suggestions. I’m leaning back towards intermittent electrical problem of some sort. In addition to the hot idle stumble it’s also missing under moderate acceleration. It will stumble then randomly smooth out perfect, then stumble again.
I have spare PCM’s and I’ll try that. Also plan to check for voltage fluctuations at the sensors and injectors.
The Opti was rebuilt during the swap and it has the desired OEM Mitsubishi sensor. It was also converted to vented which is an upgrade. I’m not ruling out the opti just yet, however a great deal of attention was paid to it during the swap process to minimize the known troubles it can have. And there’s probably only been a thousand miles out on the car since the swap.
I have spare PCM’s and I’ll try that. Also plan to check for voltage fluctuations at the sensors and injectors.
The Opti was rebuilt during the swap and it has the desired OEM Mitsubishi sensor. It was also converted to vented which is an upgrade. I’m not ruling out the opti just yet, however a great deal of attention was paid to it during the swap process to minimize the known troubles it can have. And there’s probably only been a thousand miles out on the car since the swap.
PCM was tuned but still has full capacity to throw codes on any of the critical operating stuff. Despite the stumble I’m experiencing, it’s not throwing any codes.
The EGR has been deleted and a block off plate installed. EGR control is turned off in the tune.
The EGR has been deleted and a block off plate installed. EGR control is turned off in the tune.
A bad OPTI will break up in the upper RPMs, that's what I've seen with the LT1. Bad ICM will break up at idle and light load when it's hot, sometimes not even start.
My first car was a 1995 Z28, did a few things to it and worked on quite a few LT1 cars. Then got tired of it and swapped in a 408ci LS Engine. 🙂
My first car was a 1995 Z28, did a few things to it and worked on quite a few LT1 cars. Then got tired of it and swapped in a 408ci LS Engine. 🙂
- Status
Similar threads
