'95 Vette LT1 - low RPM pinging?

[zeitgeist57]

Just this week I've noticed that when I'm shifting gears and pushing the gas in any low rpm (2k or below) driving situation usually around town, the car makes a terrible pinging clatter. Sounds almost like it's dieseling. I'm not pushing the throttle hard at all. It's just pinging like crazy without bogging down.

 

I can't feel any loss of performance, nor does it hesitate, have difficulty starting up, or miss in the upper RPM's. Please help!

 

EDIT: P.s...the Optispark and wires were never changed as far as I know (bought it with 49k miles on it). Spark plugs replaced last summer with Bosch +4. Car now has 66k miles. Only mods are a Jet performance chip and a K&N air filter. Always running 93 octane and synthetic oil.

[rl]

part throttle detonation is most generally linked to a poorly functioning EGR valve.

[Nate1647545505]

Clay,

 

First - Thank you for coming out last night to campus and helping out. Your meal is still on me next time out.

 

Second - Is there anyway to unplug the vacumn signal to the Opti? Pinging is usually the effect of to lean fueling, and/or to advanced timing. If unpluging it kills the ping, then there is to much advance under vacumn

 

Usually if the Opti fails completely, it leaves the car on the side of the road, and won't start. It would be pretty obvious if spark timing was off in brisk accelerations, also.

 

HTH,

Nathan

[Nate1647545505]

Originally posted by rl:

part throttle detonation is most generally linked to a poorly functioning EGR valve.

thats what I was just about to add

[nathan]

The Jet chip is probably the causal agent as it is advancing the timing to get more HP. The SES would come on if the EGR was malfunctioning since he has an LT1.

[ORourke]

Originally posted by nathan96:

The Jet chip is probably the causal agent as it is advancing the timing to get more HP.

+1

 

LT1's have an aggressive stock timing curve, there's no need to advance it with the stock cam. Go back to stock and see what happens. You might also try running some race gas to make sure it's actually detonation and not something else making that noise.

[zeitgeist57]

Damn.

 

I thought it was cool that the Jet chip was on the car, but I've heard from others and now CR that it's a worthless piece of crap.

 

Removing it when the rain dies down...

 

Is the Jet chip something I would want if I was running a nitrous wet kit? smile.gif

[ORourke]

Hell no, put it on ebay. Advancing the stock timing and then spraying it is a bad idea. If anything you'd want an msd box or something similar to retard the timing a bit depending on how much nitrous you're using.

[nathan]

+1 retard timing so you will not go BOOM! Check out madz28.com or pcmforless.com for programming solutions. You should be able to cover the expense of programming by selling the JET chip

[Lustalbert]

also, check the tps with a vom. see if it is smooth all the way through the throttle progression. it could be developing a bad spot in the lower throttle openings, since that is where is spends most of its time.

if its an intermittent deadspot, the computer could be seeing a closed throttle and be cutting the fuel emough to lean it out and ping.

[Guest TGrant]

Originally posted by Lustalbert:

also, check the tps with a vom. see if it is smooth all the way through the throttle progression. it could be developing a bad spot in the lower throttle openings, since that is where is spends most of its time.

if its an intermittent deadspot, the computer could be seeing a closed throttle and be cutting the fuel emough to lean it out and ping.

You arent really going to be able to tell if it is smooth or not on a dmm. If you know anyone that owns a shop or works in one they should have access to an oscilliscope. This would be the proper way of checking your the voltage signal coming from your tps. But try getting rid of your chip first.

[Dave1647545494]

I would hook it up to a scanner and then drive it so you can watch all the values in real time. if the ses light is not the detonation is probably from the chip... I ran the same kind of chip on my dakota with spray but only to eliminate the speed limiter...

[Nitrousbird]

#1: Remove the Jet programming. Hell, I think I am able to tune your car via Tunercat I have; I have the 95 cable, unless the Vette PCM is different enough not to allow it. Assuming you really need any sort of tuning anyway; it's pretty good from the factory on a stock setup. I do have Datamaster EE Beta that can do the scan.

 

#2: Possible bad gas.

 

#3: I doubt it is the EGR systems. I could not tell any sort of difference w/ the car when I removed the EGR system. My roomate never had a problem w/ his gone...nor have I found anyone having a problem going !EGR on the reaseach I did before I decided to go do it. You could always pull the plug to the unit itself (back driver's side of the intake manifold) to find out.

 

#4: Though the Opti is unfairly blammed for everything, and you do have the better vented 95-97 Opti, it could be starting to fail.

 

I'd say if you noticed it just this week, try some new gas first. Then pull the Jet Programming (it's not a chip people). Always go w/ the easiest solutions first.

 

Also, does it do this when cold, or only when the car is warmed up??

[nathan]

Joe, I disagree, the Jet Chip plugs into the harness before the PCM on his car. They do not do custom PCM programming at JET as far as I know, they just sell those modules. That is why I suggested he contain Ion or Bryan. Also the opti would most likely be felt more at high rpms. It is commonly the culprit for the high miss that a lot of LT1 owners complain about. I suppose if the gas really wasn't the octane that it stated, that could throw off what the JET chip is expecting to see creating the detonation problem too.

[Nitrousbird]

Originally posted by nathan96:

Joe, I disagree, the Jet Chip plugs into the harness before the PCM on his car. They do not do custom PCM programming at JET as far as I know, they just sell those modules. That is why I suggested he contain Ion or Bryan. Also the opti would most likely be felt more at high rpms. It is commonly the culprit for the high miss that a lot of LT1 owners complain about. I suppose if the gas really wasn't the octane that it stated, that could throw off what the JET chip is expecting to see creating the detonation problem too.

I didn't realize Jet was a piggy-back module (as not many people run these); I figured it was the same as a Hyperjunk, just a PCM flasher. Regardless, unplug it.

 

When my Opti went, I never had a high miss, it actually ran like crap in lower RPM's. That said, the Opti died VERY soon afterwords (like later that day).

 

Bad gas doesn't necessarily mean low ocatane. Could be simply too much water in it. I'm no gasoline expert or anything, but I know I've had a couple of bad batches in daily drivers that the car just doesn't run as well until my next fill up, and fine from then on.

[zeitgeist57]

Jet, bad gas, or Opti are probably the possible reasons. It hasn't really done it these past few days as far as I can discern. I still haven't done it yet, but I'll yank the Jet module this week and see if anything improves.

 

The Opti is scaring me at almost 67k miles on the odo. I'm half tempted to get the Delteq stand-alone ignition system just so that I don't have to fuck around with swapping out the Opti or just a cap and rotor.

[Nitrousbird]

Originally posted by Zeitgeist:

Jet, bad gas, or Opti are probably the possible reasons. It hasn't really done it these past few days as far as I can discern. I still haven't done it yet, but I'll yank the Jet module this week and see if anything improves.

 

The Opti is scaring me at almost 67k miles on the odo. I'm half tempted to get the Delteq stand-alone ignition system just so that I don't have to fuck around with swapping out the Opti or just a cap and rotor.

The Delteq Stage I (haven't checked to see if the stage II setup has been released yet...probably not) and LTCC both still require the use of the optical side of the opti, so if that is going, you are still screwed. But 67k isn't really that bad; my non-vented lasted until 80k of abuse, 30k of that w/ an aftermarket coil and ignition.

[zeitgeist57]

Still got the aftermarket coil and ignition? smile.gif

 

My other option is to slap on an MSD box and roast that Opti to kingdom come smile.gif I've never done an MSD install though.

[nathan]

Hadn't thought of water in the gas, that could be a problem too. Those Coil Pack setups are great if you are turning over 7k, but for most of us they are really not a high priority. The pain of the opti is the cost and the install. Where did you fill up, so that we can all avoid that place?

[Nitrousbird]

Originally posted by Zeitgeist:

Still got the aftermarket coil and ignition? smile.gif

 

My other option is to slap on an MSD box and roast that Opti to kingdom come smile.gif I've never done an MSD install though.

Yeah. I run a Mallory Hyfire IV and an MSD coil. I am one of the lucky ones who has never had a problem w/ their MSD coil. I went through 3 MSD Digital 6+ (good warranties, thank god)boxes before selling it for the less expensive and far more feature rich Mallory unit.

 

Unless you are going w/ a power adder, or a big dollar N/A setup, an aftermarket igntion and coil would be a complete waste of money. The Delteq and LTCC units aren't really useful for near stock cars either. And at $190 shipped for a new vented GM opti, it's not all that expensive to replace.