Need help getting 1991 back in operation
 

History:
Original owner, un-modified 1991 with 85k miles - been stored for last 10 years. Trying to get it back on the road.

Issue:
Failing smog test for nitrous oxides [697 ppm vs max 545 ppm at 15 mph. OK, but only just at 25 mph] - CO percentage is twice the max at both speeds and hydrocarbons [103 ppm vs 78 max at 15mph, again just OK at 25 mph]
I sense a very slight occasional surging around 2000+ rpm cycling at around 50 Hz. Don't get anything unusual on the tech 1 using snapshot.

Recent maintenance:
New fuel pumps & filter
New plugs
Repaired vacuum line that was disconnected
New fuel injectors

No codes

Diagnostic Circuit Check with Tech 1
All items in range except:
Blk Learn Enable has value YES and should be NO
Spark advance is 11 degrees and should be 0 degrees

Checked fuel pump operation:
Intial pressure peaks at 58psi and immediately drops to a steady 50 psi and holds. [I assume this means the pump is generating plenty pressure and the regulator valve is also working]
At idle get around 45-46 psi. [I think it's supposed to drop 3-5 psi but not certain]

To do's:
Check spark
Check A.I.R.
Replace O2 sensors - maybe?

Any suggestions? [Other than CA smog test sucks :)]

Appreciate any help.

Cheers,
Don MacLennan

Re: Need help getting 1991 back in operation
 

I would give Marc Haibeck a call and discuss it with him. Marc has put together some calibrations along with a few other tricks to get California cars compliant, so I'd start with Marc, the ZR-1 Specialist.

Re: Need help getting 1991 back in operation
 

Is this in Closed Loop? What do the O2 sensors say?

Re: Need help getting 1991 back in operation
 

Yes. Closed loop.

O2 sensors are reading from about 100 mV up to 700 mV or so. Hard to say precise numbers. Snapshot gave mid 300 mV on both.

Thanks

Re: Need help getting 1991 back in operation
 

Absoluteley. Used his video to do the injectors. Want to make sure all the obvious stuff is done first.

Re: Need help getting 1991 back in operation
 

Ok, so if its C/L, then what are the BLMs like?

Re: Need help getting 1991 back in operation
 

L. INT 127; R. INT 126
L. BLM 122; R. BLM 125

Thanks

Re: Need help getting 1991 back in operation
 

Where in CA are you? Just so you know you are not alone in having great difficulty getting these cars to pass on CA. It has been reported many times over that CA has actually tightened the qualification numbers to a level well under what was required when the cars were new. The state in its over zealous new age thinking is actively trying to get older cars like ours off the road. They make no exceptions like other states do for “classic” cars.

Along with what others have posted I suggest you check what chip your running. Many owners have “upgraded” to a performance chip. So let’s check for obvious first. I’ve seen quite a few that current owners had no idea they were there. Undo the 2 nuts that hold the ECM in place, lift it out and turn it over without undoing the wire connections. Undo the plate underneath and look at the chip. There should be a paper tag on the chip with the code BFXB. Performance chips will typically have the makers name and such.

The info you posted does indicate your on the rich side of things. Xfirez51 will no doubt chime in on that.
H
:cheers:

Re: Need help getting 1991 back in operation
 

I'm in San Jose. Haven't taken it to Northstar Corvettes yet, but that's my only option locally that I'm aware of if I can't solve it myself. I still have a lot of leads to work on so I'm still hopeful

I'm the original owner. No performance chips (yet.)

I agree that there is an indication of richness, however the high nitrous oxides bother me most. I can probably get to the bottom of the rich issue.

Thanks for your help.

Cheers,
Don

Re: Need help getting 1991 back in operation
 

Don,

I would go w Hans' suggestion and look at the chip. All LT-5 MY have 2 calibrations for them. If urs is AXFK, then its the original calibration and GM issued a second one which is the BFXB calibration. So I would make sure that u have the revised cal to begin w.

Re: Need help getting 1991 back in operation
 

OK. Did not know that there were 2 calibrations from GM. Do you know what the BFXB changed? It's an original CA car and passed smog through 2001 at least, possibly as late as 2009. I'll check on the chip and get back.

Thanks,
Don

Re: Need help getting 1991 back in operation
 

Im curious, do you have any of the old smog test results sheets? It would be interesting to see the old specs the state used compared to what they expect to now.

If 2009 was the last time, I assume you got all the old gasoline out and put all fresh gas in. I also assume, since you previously got it smogged there, you had it tested with the power key off, even removed, so that secondaries don’t operate.
H
:cheers:

Re: Need help getting 1991 back in operation
 

Went looking but can't find any old smog tests. Had a look at one for our 2001 XJR and almost all the requirements for it are lower than required for the ZR-1.

Can't remember about the fuel but I think I put the 5 gal or so that was pumped from the tank in my Denali - may have put it back in the ZR-1. Filled the tank completely before the first smog - that was before I pulled the plenum and she wasn't running very well. Only failed the Nitrous Oxides test on the first smog. HC and CO were well under the limits. After fixing the vacuum leak and installing new injectors I put another 10 gallons in before the second test. That's where the HC fails as well as NO. Both CO and HC emissions jumped way up after the plenum pull and new injectors. NO came down a bit. Even though CO jumped up it is still half the max.

Cheers,
Don

Re: Need help getting 1991 back in operation
 

Imagine it will be tough to get through current Cal emissions test without EGR. That was my experience in Northern VA which has the same limit values

Re: Need help getting 1991 back in operation
 

Mine is the AXFK chip. Guess I'll need to add a new chip to the repair list. Anyone know what the second chip changed?

As an update, I checked the ignition today - spark seems good on all 8. Also checked the A.I.R system using the tech 1. I can hear the pump come on for a few seconds and the O2 sensors drop to 0 mV on the left and 18 mV on the right. Seems to be working OK.

When doing the spark check, I did notice a hissing sound near the rear of the engine that lasted for 10 sec or so after shutting down. Something leaking? Is this normal?

Will investigate further.

Cheers,
Don

Re: Need help getting 1991 back in operation
 

What injectors did you install? I think I asked before but are you smog testing with the power key off or out of the car?
H
:cheers:

Re: Need help getting 1991 back in operation
 

Bought the injectors from Gerry's Gaskets. FIC.

Key was off for smog test - I think it was in the ash tray.

Cheers,
Don

Re: Need help getting 1991 back in operation
 

Got advice from Marc and I'm in the process of changing the O2 sensors. Left one was easy. Got the right one out easily but i am having difficulty getting the electrical connector installed. Another older thread suggests removing the k-frame brace. There are 4 bolts attaching the brace to the frame and a nut that appears to be attached to the engine mount. Does this nut get removed too?

Any ideas on how to get the connector re-connected?

Planning a long run with CRC 05063 after the O2 sensor is re-attached then another smog.

Cheers,
Don

Re: Need help getting 1991 back in operation
 

Bfxb was not specifically different for emissions. That likely won’t make a difference for you. Save the money.


Sent from my iPhone using ZR-1 Net Registry

Re: Need help getting 1991 back in operation
 

Yes, the nut has to come off. While it is the nut for the engine mount, it and the “K” member do not support the engine. After you have the O2 sensors in take it for a long hard drive to get the cats good and hot. Its likely the cats got a bit contaminated from that old gas, long inactivity and frequent startups without really driving it. When I still lived I CA I found that a few good full throttle runs to redline immediately before taking to the smog station brought the numbers down somewhat.
H
:cheers:

Re: Need help getting 1991 back in operation
 

Thanks, it looked a bit scary. Will get to it tomorrow and plan to empty a tank of gas to clean everything out before the next smog.

Cheers,
Don

Re: Need help getting 1991 back in operation
 

What part of California are you in? I’ve had to really work to get my bone stock 25,000 mile 91 to pass,it’s failed twice.

Re: Need help getting 1991 back in operation
 

San Jose. Plan to go to the smog shop in Mountain View. I think they test the Corvettes for Northstar Corvettes. Any suggestions on what to do to get it to pass would be appreciated. I have 85k miles on mine but it is stock too.

Re: Need help getting 1991 back in operation
 

I’m in Fremont,you need to start the registration process,get a temporary moving permit and put some miles on the car. I’ve got to get mine smogged in a few weeks. Send me a P.M. for some tips and I’ll give you my number.

Re: Need help getting 1991 back in operation
 

Getting the connector to seal is a real bastard. I used a long screwdriver,a wad of dumdum on the end of it,stuck to connector on the end of just to get the connector to line up with the other end. Once it’s lined up I used something long to oust it all the way on until it’s locked in place. Dumdum is that black seam sealer stuff used in the automotive trade.

Re: Need help getting 1991 back in operation
 

Precision Motive in Hayward has experience with ZR-1s,if you have to take it somewhere that’s an option.

Re: Need help getting 1991 back in operation
 

Take out the K frame to get to the right O2 . It is a brace only. It supplements the motor mount rigidity. It does not hold up the motor. Pulling it out does not affect motor position.
I bought another connector and made an extension for mine. Next time will be easy peasy.

Re: Need help getting 1991 back in operation
 

Whatever happened with this?

Re: Need help getting 1991 back in operation
 

Just got it smog tested yesterday - passed with flying colors. Here's what I did based upon input from Marc H.

1. Replaced O2 sensors - even though no codes.
2. Changed oil and filter. Might have helped hydrocarbons a bit.
3. Put CRC Emissions Systems Cleaner in 3/4 full tank and drove it in 4th gear for about 100 miles (about 3500 rpm) with some WOT exercises. Then normal driving for another 100 miles to finish off the tank of fuel. Filled her up and drove to the smog station. Passed with no problems. Note - this was a different smog test location from the previous one and he used lower gears for both the 15 and 25 mph tests. Interesting!! Hydrocarbons are now better than average and NO gases only slightly higher than average. Both well under max allowed.

Thanks to all on the forum for your help and a BIG thanks to Marc H for his advice.

On to fixing everything else now :) Tires, brakes, suspension.....

Re: Need help getting 1991 back in operation
 

After modifying my 84 Xfire, I spent a year trying to get it passed. The “clown” doing the driving kept lugging the motor in 4th at 20mph, so my HC numbers spiked on decel.

Re: Need help getting 1991 back in operation
 

I see your car is 637,my 91 is 634 and 633 was in Livermore for awhile.

Re: Need help getting 1991 back in operation
 

I wonder if 635 and 636 were also CA originally.