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roadmasterBlue



Posts : 25
Join date : 2013-06-07

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PostSubject: Getting a little desperate...   Getting a little desperate... Icon_minitimeThu Jul 16, 2020 2:22 pm

95 RMW 132k. Developed skip in the engine which continued to get worse until it really ran rough when idling at stop or while slowing to stop. Took it to a local mechanic where he has replaced fuel pump, new wires and plugs and it still runs rough. He says there’re a dead misfire on cylinder 3 and maybe others. Spark is good on 3 so he thought it might be the injector. He changed that, and still misfires. He’s kind of at a dead end and doesn’t know where to go next. Looking for suggestions. Any help would be greatly appreciated. Also if anyone knows of a good LT1 mechanic in Central Florida, let me know. Opti was replaced about 1 month ago.
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silverfox103
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silverfox103

Posts : 3166
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Age : 71
Location : Littleton, NH & St. Simons, GA

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PostSubject: Re: Getting a little desperate...   Getting a little desperate... Icon_minitimeThu Jul 16, 2020 2:46 pm

If it is an aftermarket replacement from China, I'm guessing that is your problem. Lot of guys who have tried them, don't have good luck. OPTI's (original) get blamed for a lot of problems but are seldom the problem.

Tom
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roadmasterBlue



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Join date : 2013-06-07

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PostSubject: Re: Getting a little desperate...   Getting a little desperate... Icon_minitimeThu Jul 16, 2020 3:08 pm

It was AC DELCO. I thought it was NOS. So it’s likely the opti?
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Rev Bob



Posts : 311
Join date : 2016-05-24

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PostSubject: Re: Getting a little desperate...   Getting a little desperate... Icon_minitimeThu Jul 16, 2020 5:04 pm

"" So it’s likely the opti?""

""get blamed for a lot of problems but are seldom the problem.""

Its easy enough to disconnect the wire to the suspected cylinder and plug in a spare spark plug to see how it fires. Even the stock ignition has enough oomph to fire across a wide gap.

If it gives a good spark, its not the cause of a dead cylinder.

Any good mechanic can troubleshoot the LT1. There is nothing magical about their basic operation.
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roadmasterBlue



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Join date : 2013-06-07

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PostSubject: Re: Getting a little desperate...   Getting a little desperate... Icon_minitimeThu Jul 16, 2020 6:14 pm

I think he’s done that and the spark was fine. What could be the cause of a dead cylinder if spark is ok and fuel is there? He said compression is good and spark seems ok.
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sherlock9c1



Posts : 2225
Join date : 2009-05-28
Location : Huntsville, AL

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PostSubject: Re: Getting a little desperate...   Getting a little desperate... Icon_minitimeFri Jul 17, 2020 9:39 am

Gas engines need spark, fuel and compression to run. It's gotta be one of those three.

If he replaced the fuel sending unit, have him check fuel pressure. There was a recent run of delco/delphi sending units with an incorrectly spec'd hose that doesn't handle pressure.

On an LT1 I'd also replace the coil and ignition control module.
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sherlock9c1



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PostSubject: Re: Getting a little desperate...   Getting a little desperate... Icon_minitimeFri Jul 17, 2020 10:22 am

How did he verify the injector is firing? I usually use a big screwdriver and put the tip on the injector body and the handle against my ear and you can hear it clicking.

I think it was on LT1s that if you disconnect an injector while the engine is running, then plug it back in, the PCM will NOT turn that injector immediately back on.
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Rev Bob



Posts : 311
Join date : 2016-05-24

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PostSubject: Re: Getting a little desperate...   Getting a little desperate... Icon_minitimeFri Jul 17, 2020 1:14 pm

""What could be the cause of a dead cylinder if spark is ok and fuel is there?""

Before roller lifters, shaved cam lobes would cause a dead cylinder. Roller lifters can still fail, though.

If you are certain the spark is OK, and that the injector is chattering, a compression test has to be the next step.
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sherlock9c1



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PostSubject: Re: Getting a little desperate...   Getting a little desperate... Icon_minitimeFri Jul 17, 2020 4:12 pm

If you have a wiped cam lobe, you'll have a pair of dead cylinders - 3-4, 5-6, etc. Been there diagnosed that.  And the motor will be making death noises while it's idling. Just had to pull the valve covers and you could see which rockers weren't hardly moving.
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roadmasterBlue



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PostSubject: Re: Getting a little desperate...   Getting a little desperate... Icon_minitimeSat Jul 18, 2020 10:25 am

Spoke with the mechanic yesterday afternoon and told him I’d like to see what kind of responses I’d get from this forum over the weekend before trying anything else. Luckily, I’m in no rush and he’s willing to keep the car while looking for next steps. To summarize what’s been done so far; new fuel pump, new plugs and wires, new injector on dead cylinder #3. None of these have solved the misfire issue. Any suggestions appreciated. Right now it looks like the most likely next step is coil/icm.
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Rev Bob



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PostSubject: Re: Getting a little desperate...   Getting a little desperate... Icon_minitimeSat Jul 18, 2020 12:54 pm

Compression test?
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roadmasterBlue



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PostSubject: Re: Getting a little desperate...   Getting a little desperate... Icon_minitimeSat Jul 18, 2020 4:05 pm

He’s done that and said compression was good. Not sure what it was but he said it’s good. Any chance you could have this problem with bad vacuum line?
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Rev Bob



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PostSubject: Re: Getting a little desperate...   Getting a little desperate... Icon_minitimeSun Jul 19, 2020 8:14 am

Probably not. Anything that uses vacuum would not affect only one cylinder.
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dmg4
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dmg4

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PostSubject: Re: Getting a little desperate...   Getting a little desperate... Icon_minitimeSun Jul 19, 2020 8:48 am

Not to be mean, but is there any possibility that wires were switched at the plug or opti end? That could likely cause 2 dead cylinders, but perhaps not. You'd still get spark, but not at the right time.
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sherlock9c1



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PostSubject: Re: Getting a little desperate...   Getting a little desperate... Icon_minitimeSun Jul 19, 2020 3:13 pm

I would also try swapping the injector and spark plug from cylinder three to (two) different cylinders, then see where the misfire goes.
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dmg4
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dmg4

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PostSubject: Re: Getting a little desperate...   Getting a little desperate... Icon_minitimeSun Jul 19, 2020 3:25 pm

Ah yes, I had missed the fact that the injectors had also been serviced. It's an easy mistake to make, and fortunately also easy to diagnose.

But, if this turns out to be the issue, find another mechanic. It's OK to make this mistake, but not to figure out the cause if it's your job.
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roadmasterBlue



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PostSubject: Re: Getting a little desperate...   Getting a little desperate... Icon_minitimeFri Jul 31, 2020 7:48 pm

I hate to say, the problem has not been solved. The only thing that’s been done is replacement of coil/icm. He’s gone on vacation for a week starting tonight for a week, but he was nice enough to put the car inside since we are under hurricane warning. So, I’ve got more time to decide what to do next. He’s convinced there’s nothing mechanically wrong - good compression etc. Just rough running with misfire. He’s suggesting next step should be opti but I’m not sure since it was just changed a couple of months ago. Any ideas appreciated. I think it’s driving both of us nuts. I really love this car and want to keep it going for an least a few more years. Other than the current issue, it’s been a great car and is in overall excellent condition. In Florida and garaged it’s whole 25 years. Even the mechanic says it’s in great shape. Just need to get this current problem figured out. Many thanks in advance.
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booster



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Join date : 2020-04-21

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PostSubject: Re: Getting a little desperate...   Getting a little desperate... Icon_minitimeFri Jul 31, 2020 9:04 pm

If it was one of the Chinese replacement optispark distributors, having a failure in only a few months seems to be pretty common from what I read when I was looking for information on them after getting the RMW. If it doesn't have the Mitsu sensor in it, which it won't in new ones they seem to be quite unreliable.
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roadmasterBlue



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PostSubject: Re: Getting a little desperate...   Getting a little desperate... Icon_minitimeSat Aug 01, 2020 12:54 pm

First of all, I apologize for being so ignorant on thes things. While trying to research the whole opti thing on the internet, I keep seeing mention of cap and rotor only vs the “whole opti”. Can somebody explain what this means. The part I replaced a couple of months ago was:
ACDelco D8301 GM Original Equipment Ignition Distributor Cap and Rotor Kit with Housing, Seals, and Bolts. Sounds like maybe I just replaced the cap and rotor. What else could be replaced that may be causing the problem? Again, thanks in advance
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Rev Bob



Posts : 311
Join date : 2016-05-24

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PostSubject: Re: Getting a little desperate...   Getting a little desperate... Icon_minitimeSun Aug 02, 2020 6:17 am

Those are pretty much the only "wear" parts in the opti. The pickup that passes the camshaft signal to the ECM would not cause a problem on only one cylinder.
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goldwolfnhn



Posts : 149
Join date : 2019-07-11
Location : De Pere, Wisconsin

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PostSubject: Re: Getting a little desperate...   Getting a little desperate... Icon_minitimeMon Aug 17, 2020 7:18 pm

had a performance issue with my 94 rmw and had my mechanic take a ride in it with me when it was acting up and he said it was a miss but I was too cheap at the time to pay for the shop to do a proper diagnostic on the car, but I replaced the coolant temp sensor that reports to the pcm, not the one that reports to the gauge, the air intake temp sensor and those both helped but when I just recently replaced the mass air flow sensor the problem went away completely, but on my car it never threw any codes.

so my recommendation would be to have your mechanic check those sensors to make sure they are reporting right, it might be a long shot but it's better then nothing.
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sdowney717



Posts : 67
Join date : 2017-01-01

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PostSubject: Re: Getting a little desperate...   Getting a little desperate... Icon_minitimeMon Oct 05, 2020 9:40 am

Has he check to see if the missing cylinder is getting a spark?? If so, then how could it be the opti.
I have 224,000 miles on my original opti.
One thing maybe none of you have done for a performance improvement, for my 1994, when I changed my water pump, I took off my opti and ground the 3 mounting holes oblong wider in the direction of advancing the opti  distributer, and it worked, the engine picked up more power, it was easy to tell when driving. And no pinging either. I was able to advance opti a little more than 1/8". All 3 bolts still hold it on fine, you grind so that distributer moves against direction of crank rotation. Apparently there is enough slop in the knox  sensor programming (regular fuel too) to advance without detonating.
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