girvin02

Like several people on here, my LT1 is giving me fits. I first thought I had a fuel pressure problem. Now I think it is a spark problem. The car does not throw a code, so I am shooting in the dark here. Here is a summary of what I have done thus far:

My 1994 A4 Corvette was running very rough at idle & at part throttle (severe hesitation/miss) but ran ok at WOT.

1. Replaced spark plugs (AC Delco standard plugs - not of the platinum variety - gapped @ .050"), fuel filter & air filter. No change in performance.
2. Replaced distributor cap/rotor, plug wires, PCV valve, coolant temperature sensor. Car ran worse - same problems as before, but now underpowered (felt like running on 7 cylinders). Noticed a very loud "clicking" fuel injector.
3. Replaced all injectors with Ford Racing "blue top" 24# injectors (matched set). Car regained full power but still ran rough once it reached normal operating temperature (erratic idle & part throttle hesitation/miss). Also noticed engine cutting out at high RPM.
4. Used paper clip to pull codes: 4. H77, 9. H72 (nothing indicating engine trouble).
5. Replaced (2) front o2 sensors - no noticeable difference.
6. Replaced ignition coil & ignition module - no noticable difference.
7. Fuel pressure checked out ok (45 psi @ idle, 43 psi @ WOT).
8. Replaced opti-spark distributor w\ cheapo Al Cardone ($139) remanufactured unit. This fixed the erratic idle. Part throttle hesitation remained. High RPM surge felt different. Now it is a noticeable miss, sometimes actually causing backfire (popping sound).
9. Removed old (stretched out) top throttle body gasket. Used Permatex (black) gasket maker to seal throttle body cover plate (also known as the clean air plate). This cured the part throttle hesitation and greatly improved throttle response. Car now runs better than ever up to 5,000 RPM, where it starts missing/popping until I let off the gas (only once engine has reached normal operating temperature).
10 Cleaned MAF sensor - no noticeable difference.

I have read of at least one other forum member who had bad luck with a remanufactured opti-spark. Is that the most logical place to start? The only other thing that I can think of is to put less gap in the spark plugs and see if that cures the high RPM miss (in which case, I would replace them with platinum plugs). Any ideas from someone who has tackled a similar problem would be MUCH appreciated.

onedef92

My advice? When it's time to replace your LT1's Optispark distributor, don't settle for a remanufactured unit when you can buy a brand new one. Opti's have come down considerably over the last six years.

GM Performance Parts offers new replacement Optispark distributors that are guaranteed to fit and perform like the General intended.

You can also get high-quality units from DynaSpark and MSD, although the latter only recently appeared on the market and long-term results are pending.

pcolt94

Where did you ever find a rebuilt opti, never knew on existed.

Here is another option

If your interested, here is a site for a GM unit for about $300 brand new. I got mine here and the site is reliable.

http://cgi.ebay.com/ebaymotors/92-93...spagenameZWDVW

SJW

I'd suggest that you check the connections to the ECT sensor. You noted that you've already replaced the ECT sensor, but the temp-related aspect of this makes me suspect that the ECM may not be seeing accurate ECT inputs, so double-check the connections at the sensor.

I'd also run a sweep test of the TPS, although I doubt you'll find the source of your problem there.

Be well,

SJW

DougSilver

Other items in the list of usual suspects might include coil and/or coil module. What about the egr--is that operating correctly?

Randy93

Like so many have said before me, STOP throwing money at the problem. Take the time to track down your problem, I have the same problem as you and I have come to realize I have a bad wire somewhere, plus blocked cats and maybe something else but not sure.
I am tracking the wire down and then will tackle the cats and then will see. When cars get older, these tiny wires do break or get corroded, so start there and work your way to the problem.

DougSilver

How did you end up realizing (suspecting?) that you have a bad wire somewhere? My impression about these cars is that diagnostics can be next to useless due to the fact that (1) the car can run like absolute garbage and still not throw a code and (2) most mechanics these days that might have the right type of diagnostic equipment will not have the patience to start tracking down an intermittent problem. This might date me but I long for the good old days when a mechanic could look and listen to a car for a minute or two and know what was wrong--no such mechanics seem to exist today.

Randy93

I started OHMing the wires one at a time, for my IAC and O2, etc and noticed when I moved the wire while trying to keep my balance, the OHM meter bounced to 0 and then backup. So I started moving the plug while keeping keeping my leads on them and everytime it bent a certain direction, the needle would drop to 0. Ask other people, I am a beginner when it comes to electronics and do some searches. There is a lot of knowledge on this form.

girvin02

onedef92, good advice. The saying, "You get what you pay for" comes to mind.

I ordered it through a company called Murrey's Auto Parts (chain of stores in the mid-west or perhaps just Michigan). It appears to be an OEM unit that was remanufactured in Mexico by a company called Al Cardone. I paid $136 if I remember correctly and it did not come with cap/rotor (which I had already replaced with AC-Delco pieces for $250 ). I would not recommend going this route, considering my current issues. Even with the original (failing) opti, it never cut out this bad at high RPM, leading me to believe it is in fact the remanufactured opti, causing the problem.

Looks like I will be purchasing a NEW AC-Delco unit in the near future. I was thinking of ordering it from Summit ($379.88) but instead will probably order it from the ebay seller that you provided a link for - Thanks pcolt94!

SJW, the ECT connector is firmly in place and in good condition. I have not done a sweep test of the TPS, but also doubt that is the problem, as the car idles perfectly.

Dougsilver, the coil is new (and tests good) and if by coil module you mean the ignition control module, that is new also. I have not tested the EGR, and to be honest, do not know the correct procedure to test it.

Thanks for the input guys.

LT14FUN

Just got done putting a Dynaspark in my '92 - yeah, I've been through them mill on this. Original Opti crapped out at 60K - no codes - replaced with an AutoZone remanufactured unit - ran fine UNTIL it got to operating temp - then it would die just like the ignition was turned off. Again, no codes.

Turned out the remanufactured Opti had a open circuit when hot - had a one year warranty, but was void since I modified it to vent it.

Bought an AC-Delco from Superior - supposed to be OEM, but I've heard these are remanufactured too. It lasted 2 years - car died without even a wimper - no start - no codes. You can check my other thread on this (search my user name LT14FUN).

The Dyna is in as of today and she runs better than ever - now I have a warranty just in case. Good luck on yours -

bowtie350_428

Hey girvin02, have you got an Update? I am in the same boat you are with my 94 TA. I replace pretty much the same as you and still no luck. Let us know.