'95 LT-1 Engine stumbles under high load
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Joined: May 2003
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From: fort mill sc
'95 LT-1 Engine stumbles under high load
Posted this before. Got advice it might be OPTI. Replaced plugs this weekend and 75% problem is gone. Previously, any high load - high RPM (> 4500) was a problem. New plugs have completely eliminated problem when auto trans is NOT in 1st gear. Only remaining problem is 1st gear >4500 RPM and full throttle. If I back off accelerator 1/4 inch it WON"T stumble. High speed downshifts into 2nd NEVER stumbles or backfires. The BOSCH dual electrode plugs run great. Any ideas why only problem in 1sr gear and at WOT (wide open throttle)?
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Re: '95 LT-1 Engine stumbles under high load (rmd8136)
Two separate cases happened to me with what you describe.
Case #1, my '95 was missing at anything over 4500 rpm, but only under load(can't explain why really), but in neutral I could take it to 5000 without a stumble.
Also I would have a no start condition. Turned out to be the coil wire rubbing on the waterpump.
Case #2, my '93 was missing at anything over 4500 rpm, again only under load. Two plug wires were touching the exhaust manifolds. New plugs and wires solved that problem, but only in dry weather. After a hard rain or long period of inactivity, the car would act up. Ended up being the opti. Didn't change it, but did a conversion to the LS1 setup. That solved the problem(although a little pricey at $725)
For your '95 I'm fairly confident that if you replace the opti, all will be well. The opti in my '95 was replaced only becasue the waterpump was being done at the same time, so I didn't want to do it twice. No problems (except for the coil wire) in 53,000 miles.
Case #1, my '95 was missing at anything over 4500 rpm, but only under load(can't explain why really), but in neutral I could take it to 5000 without a stumble.
Also I would have a no start condition. Turned out to be the coil wire rubbing on the waterpump.
Case #2, my '93 was missing at anything over 4500 rpm, again only under load. Two plug wires were touching the exhaust manifolds. New plugs and wires solved that problem, but only in dry weather. After a hard rain or long period of inactivity, the car would act up. Ended up being the opti. Didn't change it, but did a conversion to the LS1 setup. That solved the problem(although a little pricey at $725)
For your '95 I'm fairly confident that if you replace the opti, all will be well. The opti in my '95 was replaced only becasue the waterpump was being done at the same time, so I didn't want to do it twice. No problems (except for the coil wire) in 53,000 miles.
Racer
Joined: Jul 2003
Posts: 287
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From: sykesville md
Re: '95 LT-1 Engine stumbles under high load (rmd8136)
My 92 is doing the same . I replaced the opti , wires & plugs . I think i maybe floating valves . I had the rev limiter raised thought i could hitting that not the case. Two mechanics never saw anything like it. :skep:
Team Owner
Joined: Aug 2000
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From: San Pedro CA
Re: '95 LT-1 Engine stumbles under high load (bstirn)
load versus no load have a HUGE impact on how a car will run.
Under load is the only way to effectively test an engine... without load, it will just spin and any ignition or fuel delivery problems are lost in the inertia.
With load, that inertia is not present, so the engine has to work... and if something does not, then you have a problem.
Bstirn - raising the rev limiter is not a good idea, unless you have enough valve train to work with it. Beleive me, when you hit the limiter, you HIT IT. HARD. It is not confused with a miss or high RPM stumble.
The rev limiter will retard timing and stop fuel for an instant... you will know it... even if there is a misfire, the compression and heat in the head could be enough to ignite some of the charge, however, when there is no fuel, no fire.... major misfire!
I would agree the opti is the main source of the problem...
Oh, I talked with Bob from LTCC about the wires, to quote, or, at the very least, accurately paraphrase: "I need to update the web site, get the Taylor cut to fits".
Under load is the only way to effectively test an engine... without load, it will just spin and any ignition or fuel delivery problems are lost in the inertia.
With load, that inertia is not present, so the engine has to work... and if something does not, then you have a problem.
Bstirn - raising the rev limiter is not a good idea, unless you have enough valve train to work with it. Beleive me, when you hit the limiter, you HIT IT. HARD. It is not confused with a miss or high RPM stumble.
The rev limiter will retard timing and stop fuel for an instant... you will know it... even if there is a misfire, the compression and heat in the head could be enough to ignite some of the charge, however, when there is no fuel, no fire.... major misfire!
I would agree the opti is the main source of the problem...
Oh, I talked with Bob from LTCC about the wires, to quote, or, at the very least, accurately paraphrase: "I need to update the web site, get the Taylor cut to fits".
Racer
Joined: Jul 2003
Posts: 287
Likes: 1
From: sykesville md
Re: '95 LT-1 Engine stumbles under high load (bogus)
What do you think could be happenin. I give up. Unless valve springs help. Should i replace them and do 1.6 RR while im there Youre input is appreciated.
