1990 exhaust manifold issue...

[bdw18_123]

Ok, guys, got a bit of an issue here. Kinda kickin myself in the azz for not catching this before reassembly, but what is done is done.

My Z had been driving great, but after a couple high speed runs, started getting a check engine light. The first time it came on, it took awhile for it to come on again the next time I drove it. But then after several more drives, it pretty much started coming on within 5 minutes or so of turning the car off, then on again to get the light to go out. If I disconnect the battery long enough, it takes awhile for the light to come on again on subsequent drives, presumably because doing that wipes the learning that the ECM recorded. Also, after the light comes on several times, I notice that the instant fuel mileage is worse than before the light comes on. I happened to be under the car and I noticed that the passenger side cat rings like a bell when hit with a wrench. Driver's side doesn't do that, is a dull thud sound. Obviously, the substrate is gone on the passenger side. Dammit!!

After pulling the codes several times, I keep getting codes 44 (left oxygen sensor circuit - lean exhaust indicated) and 55 (fuel lean monitor), which seems a bit odd since it's the right side that has the substrate missing. I figure these codes are most likely the result of having substrate in one cat and none in the other causing an imbalance, especially at higher rpm's. This is also most likely why the mileage starts to suffer, since the ECM is probably trying to compensate for the lean condition.

Being that the going rate for a full set of stock exhaust manifolds is around $300-$400 (depending on mileage), it doesn't make sense to get those. I can't afford it anyway. However, if I went with the $450 OBX headers (from what some here have reported, quality is pretty good for the price), I'd most likely have to change my whole exhaust system (putting headers with stock exhaust doesn't make sense either) and I REALLY can't afford that. I'm in Cali, so those are illegal anyway.

Question - Will it damage my engine to drive it like this? Since as I said, I can't afford $300+ for stock manifolds or the headers, but I want be able to drive the damn thing, I worked on it for over 2 years.

What say the ZR-1 experts?

[GOLDCYLON]

This thread came to mind


http://www.zr1.net/forum/showthread....ght=converters

[Ccmano]

or these (not mine) $200....

http://cgi.ebay.com/ebaymotors/1991-...item415ab7ed0c

H

[bdw18_123]

Goldcylon - Interesting thread, but my engine doesn't seem to smoke or use oil. I did have chips in the nikasil coating on one liner on the RT side, but I replaced that liner with a not-quite-new one and the piston rings (a used set) on that piston that Jerry sent me. The engine runs great and has good power (when the check engine light is not on).

Ccmano - Those might be worth looking into, except that they are in Michigan and that listing says pick up only. So that wouldn't really work.


So I'm still left with my question, will it harm my engine to drive it with no cat internals on the RT side?

[XfireZ51]

I think your motor is going lean on the left side. The cat wouldn't affect that. Is it happening at just cruise or during WOT? May want to ohm out the injectors as a start. Your mileage is suffering because with a lean condition, the ECM is pulling timing.

[GOLDCYLON]

Originally Posted by Dynomite

40 miles from you sitting out by mail box (only 50K miles 91' Z) ....you have a PM....they are free. A rarity in CA since no one removes stock exhaust systems......except me on a 90' (L98) and on a 91' (LT5)

Cliff

Nice offer Cliff !

[bdw18_123]

Cliff - Wow, what can I say, that is extremely nice of you to offer those and only 40 miles away too! I will take them. The ZR-1 Brotherhood is awesome!

Xfire - So you don't think that having no cat substrate on the right side would have any negative effect at all on how the engine runs? Hmm...

Well the injectors are replacements from FIC (Bosch II's, yellow/silver body), I sent the ones that came with the car back to him, since they had been sitting for several years and he said he didn't like how they performed so he sent me back a different set of rebuilt set of Bosch II's at no charge, so I'm pretty sure those are good. Though I suppose it wouldn't hurt to check anyway.

The ECM that came with the car (was a replacement, done in 2001) was determined to cause misfires (credit for that discovery goes to tccrabs as I had loaned him my ECM back aways, thanks Tom!), so I have another GM original, non-rebuilt ECM in the car that I got from Sgreg that he said came from a Z (think it was a '91?) with only around 30K miles, with the PROM swapped in from the ECM that came with my car.


Besides injectors, what else might be the cause of a lean condition on the left side? The first time the light comes on is usually after I go to higher RPM's (like between 5-7 or so), just before it comes on, I can feel the power cut out, probably 'cus the ECM is trying to compensate. But once it starts coming on more often, it comes on even at cruising.

[XfireZ51]

Originally Posted by bdw18_123

Cliff - Wow, what can I say, that is extremely nice of you to offer those and only 40 miles away too! I will take them. The ZR-1 Brotherhood is awesome!

Xfire - So you don't think that having no cat substrate on the right side would have any negative effect at all on how the engine runs? Hmm...

Well the injectors are replacements from FIC (Bosch II's, yellow/silver body), I sent the ones that came with the car back to him, since they had been sitting for several years and he said he didn't like how they performed so he sent me back a different set of rebuilt set of Bosch II's at no charge, so I'm pretty sure those are good. Though I suppose it wouldn't hurt to check anyway.

The ECM that came with the car (was a replacement, done in 2001) was determined to cause misfires (credit for that discovery goes to tccrabs as I had loaned him my ECM back aways, thanks Tom!), so I have another GM original, non-rebuilt ECM in the car that I got from Sgreg that he said came from a Z (think it was a '91?) with only around 30K miles, with the PROM swapped in from the ECM that came with my car.


Besides injectors, what else might be the cause of a lean condition on the left side? The first time the light comes on is usually after I go to higher RPM's (like between 5-7 or so), just before it comes on, I can feel the power cut out, probably 'cus the ECM is trying to compensate. But once it starts coming on more often, it comes on even at cruising.

Fuel Pump. Sounds like you're running into issue of going lean at WOT and setting a lean code. After that, the secondaries are disabled so when you push it, it stumbles.

[sammy]

i agree you might ck the fuel strainer thats on the pumps, if i remember correctly your car sat for about 2 yrs ,you could have some crud in the tank from sitting that long .you could just use a siphon to take all the fuel out once and get her clean.so you know for sure . .i have seen so many guys have trouble with their car if they sat for a couple of years. heck when i got my 68 mustang running after 3 yrs down .it plugged the fuel filter in about 50 miles . hence my thoughts on what your problem might be

[bdw18_123]

The exhaust manifolds I got from Cliff are installed, I kept my original exhaust system though because it has smaller muffler cans which I think would be a bit louder than the bigger ones. Unfortunately, I still have the issue with the check engine light. Grrrrr... At first I thought I had found the source of that problem because I found that the O2 sensors in my original manifolds were only barely tight, the metal gasket wasn't even crushed. And the left sensor did seem to be a bit looser than the right.

I think that did solve part of the problem because now the check engine light is behaving a little differently than before. Before, once the light came on, it wouldn't go off until turning the car off then on again and it would usually come back within several minutes of doing that and then stay on.

But now, when it comes on after driving a ways with it on, it goes off by itself for awhile and then comes on again. It did this several times the last time I drove it and when I got home, it was idling a little rough. Then the light came on and instantly, the idle got better. With the light on, is the ECM using a base/default program to run the engine as opposed to the normal one? What would be bypassed in this case that would make it idle better in that instance?

Also, I don't seem to be able to rev much past say 5K rpm or so before the ECM shuts the secondaries off. The light does come on even at cruising though, so I don't know that the problem is coming solely from the secondary system. I need to drive it with the power key off and see if the light comes on with the secondary system disabled from the start.

Xfire - I don't think it is the fuel pumps, I replaced both with brand new ones. Plus, being that it is always only the left side throwing the lean code, I don't see how it could be that. Wouldn't a bad pump affect both sides?

sammy - The strainers are new, I replaced them when I did the pumps. Fuel filter is also new.

The only thing I can think of that would cause all these issues is maybe some of the fuel injectors on the left side are somehow bad, or not flowing as much fuel as they should? Maybe I should pull them and send them back to FIC to be checked again? Jon from FIC sent them to me in around May of this year I think, maybe I let them sit a little too long?

This problem is a bit maddening, when the secondaries are on, the thing pulls like a freight train, but the stupid ECM keeps shutting them down after a certain point. Arrg.


Maybe I'll go drive it right now with the power key off like I said and see if the light still comes on to see if it is just the secondaries or not. I'll report back what I find...