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!! :mad::mad:

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.php?t=14805&highlight=converters

[Ccmano]

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

http://cgi.ebay.com/ebaymotors/1991-CORVETTE-GM-ZR1-EXHAUST-MANIFOLDS-PIPES-/280694877452?pt=Vintage_Car_Truck_Parts_Accessorie s&hash=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]

http://i287.photobucket.com/albums/ll142/dynomite007/ZR1/ZR1Exhaust.jpg

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) :D

Cliff

Nice offer Cliff ! :hello:

[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! :cheers:

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]

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! :cheers:

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...

[a1991zr1]

check the fuel pumps and also see if injectors are leakin down on left banks. to do this pull the plugs are any fouled. with the pugs out turn the key on 10 secs then off then one more time. smell the plug holes do you smell fluid. could be leaky injectors or secondaires not seating completely. also check fuel pumps and pressure i would check the fuel pmps connector i have see these fail or become loose. pm me if this doesnot work

[bdw18_123]

Ok, just got back from a little drive. I cleared the codes first (was the same 44 & 55) and I kept the power key off the whole time. For awhile, the check engine light wasn't coming on just cruising at normal rpms, so I figured maybe get the revs up and see what happens.

So kept it in 4th and got the engine to just about 5K and then shortly after the light came on. So this isn't just a problem with the secondaries, it affects the primaries too. Got home and pulled the codes and yup, the same 44 & 55. Always the same, only the left side. The right side never throws any codes. However, from reading what the manual says on code 55, this code seems to be only for when the secondaries are enabled. How could I get this code with the power key off? Another mystery to unravel...

Several of you have suggested checking the fuel pumps, but as I have stated they are both brand new. Now I know brand new things can be bad, but like I have already asked, how can a bad fuel pump only affect the left side so consistently? That just doesn't make any sense at all.

a1991zr1 - If the injectors on the left side were leaking down, I would think I'd be getting codes indicating a too-rich condition, not a too-lean condition. I think the problem may in the injectors, but I think maybe they are not flowing enough at the higher rpms.

I haven't pulled the plugs yet, so I think tomorrow I will pull the right side and left side plugs and compare them and see how they look.

[a1991zr1]

You have a fuel problem if injectors leak down the Idc could be over compensating to much air and if secondaries are stuck open it would run lean

[Paul Workman]

It definitely sounds like a fuel related issue; similar to O2 issues and injector issues. For what it is worth, I've had a fuel pump fail right out of the box!

Note: While studying failure rate as part of a paper I was doing on MTBF, I came across several statistical analyses showing two high risk periods in the life of (both animate and inanimate) objects: Failures are low until the object reaches a certain point in it's life. At some point, the rate of failure begins to climb; gradually at first, and then the failure rate begins rising ever more quickly - don't we all know it! But, by far the most failures in a very short time occur at the onset of the object's life - resulting in the phrase, "infant mortality". It seems to defy logic: "It can't be the (so and so), it's brand new..." (And, so it was too with a new fuel pump I installed...Bad out of the box!)). Bottom line? Completely forget about age of an object...Verification is the only way to be sure it is working!

Read the plugs and compare each bank. And, if you could data log (scan) it while driving, you could gather a plethora of information about what's going on in REAL time, e.g., O2 cross counts, right and left BLMs (and injector dwell).

Injectors: Haven't seen where you've measured resistance across each injector (after the engine is good and warmed up). If they are the stock injectors, they need to be replaced. (Mine were replaced, at my request, the day before I took delivery from the dealer. Problem was, as I found out later, the were replaced with NOS and the problem with alcohol showed up again when I gave the car to Marc H for tuning. I was chagrined :o to say the least! But, I digress...) They need to be of uniform resistance (usually within a spread of an ohm), around 12.5 to 13.5, by most accounts.

All of this to say that you'll want to get to the bottom of the lean condition right away. Otherwise, you might be looking at burning a valve (or worse) and if $300 is hard to come by, try overhauling the head on an LT5! Its hard to say what could happen for sure if one side is less restricted than the other; it would depend on circumstances. The LT5 is not cheap to fix, so I would not be wanting to stress it until the known issue was resolved.

FWIW,

P.

[mike100]

it would be interesting to see what you get with a Tech1A hooked up to see what the O2's read. I would repair the bad cat to have equal restriction on both banks and possibly replace an oxygen sensor if one is lazy...at least have a 3rd one for diagnostics.

can you swap O2 sensors from left to right to see if the problem moves?

[mike100]

Outside of checking the compression and ohming out the injectors per Mark Haibecks procedure, I would scan it to see the sensor data. Of course a miss is obvious by feel and sound.

I kind of suspect a bad o2, one bum primary injector, or an air leak falseing one side or the other with a bad reading.

If you get in a bind, I do have a Tech1A that made fixing a couple of things on mine a lot easier- just have to arrange for a quick return as I wouldn't know what to do without it for long.

[bdw18_123]

Ok, please don't take this the wrong way guys, as I don't have any bad intent here, but judging by some the suggestions you are making, clearly my posts are not being read carefully enough.


First of all, 4 cats? Um, no, there are only 3 intact ones. The passenger side cat on my original passenger side exhaust manifold has NO substrate! It is just an empty can, totally empty, which is the whole reason why I put Cliff's cats on in the first place. So that manifold is useless. The driver side cat on my original driver side exhaust manifold is still totally intact, but has 140K miles on it. Using it instead of the one with only 50K doesn't make any sense.

Now the cats in the 50K exhaust manifolds from Cliff are both totally intact, I visually inspected them on both sides (thru the O2 sensor hole and thru the exhaust pipe where it connects to the rest of the exhaust system). I'm fairly sure the cats are not the issue here. Yes, I could have a bad O2 sensor, but I think that is not a very high possibility considering the type of failure and how it occurs.

Now on the fuel injectors, like I have already stated several times, they are not original. They are rebuilt Bosch II's that I got from Jon at FIC. Read my previous posts for the story on those.

As for the fuel pumps, still no one has answered this question: How can a bad fuel pump so consistently cause only the left side of the engine to be lean? It feeds both sides! It just doesn't make sense to me in this case that it would be the pumps.

Back to the original problem, I agree that it is most likely a fuel issue. We can forget about exhaust issues, I have Cliff's 50K manifolds on there, those aren't the issue.

I have a cable I made and a program that I can try to do live datalogging with on my laptop (I used it on the '93 LT1 Corvette I used to have), but I don't really know how to interpret the O2 readings, BLMs of the injectors, ect. I'll post it here when I get around to trying it, maybe one of you guys will know how to interpret it. If that doesn't work, I may need to borrow that Tech 1A of yours, Mike100. I'll have to see.


I think I may take a break from trying to figure out this problem and mess with it later. It is discouraging and I kind of don't want to deal with it right now...

[bdw18_123]

Problem is FIXED!!! :thumbsup: :dancing

Holy crap, you guys aren't kidding! When these things are running right, they do indeed pull like a freight train! I mean, it did have power before, but I could never get past 5K before the CEL came on. My ZR-1 now has the full 375HP on tap 100% of the time, with no stupid 'Check Engine Light' to shut down the fun!

Did a quick blast to 6500RPM & 140MPH in 4th (had the laptop hooked up, taking a Datamaster recording). Still gotta hit that magical 7000 number, though I was within 500RPM of it that time!

So what was the cause of the codes 44 & 55? Bad left O2 sensor! Before I replaced it, I had taken a Datamaster recording and I noticed that the left O2 sensor kept dropping to 0 volts, especially during hard acceleration. The long term fuel counts were also high on the left side at lower throttle openings (like 150-160 or so), indicating that the ECM was trying to richen the mixture on that side to compensate for what it thought was the left bank being too lean.

I showed that recording to my buddy Evan (who I work for at his performance car shop) and he agreed that it was most likely a bad left O2. I just wanted to make sure that the sensor was the issue before I went spending more money I don't have. That's why the CEL kept coming on shutting the secondaries off every time I got close to around 5K RPM. I also ohmed the left O2 sensor harness to the ECM and didn't find any issues - grounds were there and the signal line was good and not grounded.


So, I'm taking my Z on it's first Corvette Run that my other friend Pete (PLRX from the 'other' forum) is doing with a bunch of C5 & C6 people, Evan is going too. It is going to be in the mountains in my area. So there will be 2 C4's and 1 C4 ZR-1 there to remind those guys where their cars came from! :mrgreen:

[mike100]

I bet you can pass smog easily now. with a fresh valve job especially, combustion should very complete.

where's this run? I just got back in town.

[bdw18_123]

where's this run? I just got back in town.

It's here in the Sierra Nevada Mountains in Central Cali. Most of the group is actually from down south where you are, they came up here on Saturday and are staying until Tuesday (a few are going back Monday). I actually didn't even know about this run until like Wednesday of this last week and since it was in my area, I figured it would be a perfect first Corvette run for my Z.

They had runs planned in different areas in the mountains near where I live for Saturday, Sunday and Monday. Saturday's and Sunday's (today) runs were awesome, my ZR-1 has been performing great! Weather has been absolutely perfect also! Seems to be a pretty cool group of people. We all went to dinner after the runs too. Me, Pete and my buddy Evan were the only C4's.

I'm going on the run with them tomorrow (Monday) too.

[mike100]

well, I just missed it as I was flying back from Wyoming on Saturday.

Now you know the dead O2 wasted the catalyst. People shouldn't ignore check engine lights, but they do. Had you ever owned a c4 before this car? Just curious as I had a '95, but the very first Corvette I ever drove was a 91 ZR-1.

[bdw18_123]

well, I just missed it as I was flying back from Wyoming on Saturday.

Now you know the dead O2 wasted the catalyst. People shouldn't ignore check engine lights, but they do. Had you ever owned a c4 before this car? Just curious as I had a '95, but the very first Corvette I ever drove was a 91 ZR-1.

Yeah, the guy I bought my Z from, bought it new from the showroom floor. He isn't much of a mechanic, I had to undo a lot of f'd up stuff he did. I don't know how the cat in the original passenger side manifold lost the catalyst, I just know it is completely empty. My Z is running great now though, so that is all water under the bridge.

And no, this isn't my first C4, I used to have a '93 LT1 6-speed. Guess you didn't read my sig? :mrgreen:

Just got back a couple of hours ago from the 3rd day of the 3-day in a row Corvette run I mentioned. Had a blast, took tons of pics and got to know some great Corvette people.