HellaciousA

I drove the car for 3 weeks back and forth to work 5 days a week in traffic and running errands on the weekend without doing any changes to the car. I went through 2 tanks of gas, battery was never disconnected, and the problem still persists.

I just swapped o2 sensors from right to left, and the driver's side cat is still getting up to extremely high temps. The cat's themselves are brand new with less than 500 miles on them. When I inspected the o2 sensors, they both looked the same color and did not appear to have any damage.

Red 91

Check fuel pressure, and see how long it holds with engine off.

cardo0

I believe a red hot cat would be rich on that driver's side and you say you verified swapping O2 sensors that didn't change. So your batch fire on the driver's side is very rich and a scan should show longer injector pulse width on driver's side injectors. Integrator and BLM for driver's side injectors should be a small number much less than 128. Small number is lean and large number is rich. You could have open wire leads to the driver's side O2 sensor giving the ECM 0 volts from that O2 sensor indicating lean so the ECM will go very rich on that bank to richen it and that extra fuel is whats burning up your cat.

What I'm saying is you really need to get a scan and post it for us.

whalepirot

Read up on diagnosis using a vacuum gauge. It can help find restrictive exhaust, (cat or other), poor valve timing, plus vacuum leaks, etc., which can cause the EMC to 'see' a lean condition, then dump in more fuel. The overheating cat may or may not be toast (nice pun, eh?), but this looks like a left side problem. Pull the plugs and 'read' them, color and condition. Motor, and other manuals usuallly have a pictoral guide in the back.

There's more to testing FP than static idle (45 psi is ok) or bleed down time (leaking injector or seal). That original fuel pump is ok. There's variation with load, i.e. less vacuum which equals MORE fuel as manifold vacuum nears atmospheric pressure, like at full throttle.

Throwing parts is rarely the proper path and you're correct; hardly anyone wants to actually troubleshoot and fix a problem not ID'd by a code, and solved by a component swap. Ask how I know; repeatedly.

With all the mucking about by the 'pros', ensure ALL wiring and connections to sensors are clean (electronic sprays can help), unbroken and neither pinched(short) or broken. I found a pinched injector wire (constant ground) which was akin to an ECM signal to open the injector(s)- constantly! Hell, you already saw leaks after they were 'fixed'!

No experience with Optis, but also not a fan of MSD. There are spark testers that show the strength of current flow to each plug. Not an expensive tool.

Old school testing still applies in this ECM age, and some of those old tools, unfamiliar to new age techs, can find issues the ECM doesn't tag; nay, may try to cover up.

cardo0

Ok I went back to post#1 and see you changed your injectors. Did you change the tune for the new injector spec. Pulse width and injector constants need to match the injectors. I don't think there is a nice way to say what happened here so I will just shut up.

scotth48

Double check with Jon at fic to make sure you have the right injectors.
Also adjust asr cable. If slightly loose can cause throttle body not to send correct amount of fuel to match with what the computer maybe saying it needs.

scotth48

The '93 had two different injectors used with a difference in impedience values. Jon can explain that. He sent me the correct injectors and car ran great. Had many of the symptoms you were talking about.

HellaciousA

I appreciate the feedback--no need to hold back. I'm not a master tech with a full tool box of snap on tools. I'm just an average joe who is trying to help his mom fix a problem.

Here's the injectors Jon sold me:

https://fuelinjectorconnection.com/products/93-lt1

Before purchase, he verified this what I needed, so that's what I ordered. After installing the injectors, there was no change in the car's performance or driveability. It acted exactly the same once coolant temps went above 140 degrees.

I need a copy of datamaster to re-scan the car, but I can't find the setup file anywhere online. scan9495 doesn't provide clean data for you guys to help give me a better recommendation.
c

96GS#007

First I've heard of this in messing with these cars since new.

The pre-LT1 injectors ('85-'91) are different than the '92 & up LT1 injectors but I'm aware of no mid-year change to injector impedance during the '93 model run nor do the Factory Service Manual or any of the tech bulletins make mention of this.

What documentation shows this?

Only the aftermarket has offered different things depending on the style of injector being purchased.

HellaciousA

I followed page 6E3-A-81 of the service manual, and it was still showing about 1.1-1.2 volts bank 1 o2 sensor voltage with temps around 160-180 degrees. I disconnected the sensor and put my DMM in the connector and grounded it, and voltage showed .5 to .7 volts. On scan9495, the data wasn't clear, but on the chart for that bank, it was almost always at or near 1 volt, with bank 2 showing a more normal range. Per the service manual, it states to replace the ecm if the voltage doesn't go below .35 volts.

I fully expected to see an SES light show up, but none appeared. But I did get "Service ASR" and "Service Ride Control". Sounds like it's time to get a new ecm and hopefully once and for all this sorts it out.

qwiketz

this whole thing sound eerily like my situation for the past 5 years with my car. There was a break in the o2 sensor wiring (the connector sheered off). The car would run bad because timing was retarded and it would run very rich, like high tens to 11 when warm. Once fixed, car goes right to 14.7ish once into closed loop.

https://www.corvetteforum.com/forums...g-correct.html

edit... I should add that when I pulled codes on the dash, nothing showed up. My tuner spotted it when reviewing one of my datalogs. I do have a copy of datamaster setup for my 92. If you're ever down this way (kinda far) we could hook it up to the car. I rarely make it to the other side of LA though.

9T3VETTE

x3

My 93 had alot of the same symptoms and it was the ECM

MatthewMiller

Yep. My car is a 1996, but I normally run a 94/95 PCM. Even with that almost-OBD2 PCM, it didn't give me a code when my O2 sensor went out. When I threw the 96 computer in, that was the first time I got a code. So the lack of a code doesn't mean the OP's ECM is getting a good O2 signal. You can see it on a proper datalog, however.

Yeah, that's exactly what I was trying to explain earlier. Maybe I missed it, but I don't see where the OP has actually tested the wire from the O2 connector to the ECM for continuity. If that's damaged (open circuit), then it doesn't matter how good the actual sensor is - the ECM is never going to see the signal. In addition to the continuity test, a good visual check of both connectors (sensor and ECM) is in order.

ETA: I'm not saying it's impossible that the ECM is bad, and I don't know much about the pre-94 computers. However, I am skeptical that a bad ECM would really affect only one bank of the engine, and would only affect it in closed-loop operation. If the OP can locate a known good ECM really cheap, then it's reasonable to swap it in as a diagnostic test. They are super easy to swap, after all. But I wouldn't advise throwing a multi-hundred-dollar part at the problem until I did the rest of the diagnostics.

qwiketz

Edit, I meant to say knock sensor above.once again the 92/93 ecm's definitely have issues. I have had mine redone by SIA (I think that was the one) and it cost $175. It didn't fix my problems although I had hoped it would have.

You'd be amazed how brittle this wiring is now that it's 25 years old and is right next to the exhaust. Mine is worse than most due to the long tube headers, but one of the connectors crumbled in my fingers as I was trying to remove it from the sensor. I don't believe that the sensors fail that often and there is a reason that they sell replacement wiring harnesses.

As a side note, during this whole thing I learned that when you retard the timing that much, then it does cause the fuel to be unburnt to a degree and igniting late and therefore causing crazy wide band reading and glowing cats. One of my cats got so hot that it melted my racedeck flooring in my garage.

Good luck with the fix but my recommendation is check for continuity of the knock sensor wiring before burning more cash.

MatthewMiller

Oh, yes, this all makes good sense too! Very good point. If the timing is heavily retarded the engine will feel "soggy," with no snap to the throttle response. But it shouldn't run rough - it should feel luxuriously smooth, actually. IME, if the ECM is looking for a good knock sensor and none is present (no signal at all getting to the ECM), then it goes to a fail-safe mode of pulling a bunch of timing back. But you're right that it will result in still-burning mixture exiting into the exhaust, and it will heat up EGTs quite a bit and possibly overheat the cat.

That last part fits with his symptoms, but not the symptom where he says it's running rough. Still, that's an easy and worthwhile thing to check. You are sure right about the wires/connectors being subject to brutal exhaust heat, especially with headers. You're also right about the ECMs suffering breakdowns of internal circuits and even devices. It happens, no doubt. Like you, I'd like to see the OP really run the full diagnostic process before throwing more parts at the problem.

HellaciousA

I just checked continuity of both the o2 sensor wiring to the ecm and it was good, and same for the knock sensor wiring/connectors. The car has only 64k miles on it and has been garaged for most of it's life. I don't see any dry/brittle connectors really anywhere on the car. I agree that throwing money at parts to fix the problem is pointless. But I've done my best to look for frayed or damaged wiring, connectors, and grounds and can't find any. The service manual points back to doing other tests if the o2 voltage is in range, but it's pretty blunt about pointing to the ECM.

9T3VETTE

I chased wiring connections all over my car and found nothing when I was having problems. Finally I bit the bullet and sent out the ECM to SIA, hoping that was the cause (which it was).

You may have to do the same. Good luck

PatternDayTrader

What happens if you disconnect the drivers side o2 and drive the car ?

Red 91

Post #22

HellaciousA

No discerniblec change in drive quality--still bucking/surging.