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.