1990 exhaust manifold issue...

[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 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!!!

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!

[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]

Originally Posted by mike100

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.