I just picked up a 93 Z28 with about 150,000 miles. This is a summary of the vehicle history:

12/19/1993 Odometer Reading
1996 Title
1998 Title
1/23/02 110,573 Failed Emission Inspection
10/07/2002 Title
10/01/2004 Title
08/22/2005 135,169 Failed Emisson Inspection
08/22/2005 135,177 Passed Emission Inspection
9/19/2005 Title
1/25/2006 Registration Event
2/22/2006 Title

Note it failed emissions twice, only passed once, and when it did pass it did it on the same day after traveling like 8 miles. When the person I got it from drove it on the day I picked it up, there was smoke coming from the engine, and it was obviously coming from burnt engine oil. Looking at the engine, there was oil coming from the area around the oil fillter cap. It looks like it was just seeping out and falling onto a hot component in the engine compartment, producing the smoke. There was also a bit of oil coming from the rear of the valve cover, and it appeared to be seeping out of the area around the pcv valve. Looking at the valve cover on the other side, there appeared to be oil on that one too. While driving it home, the have engine serviced light came on. It seems to run very well, and idles and accelerates without any problem. When I had it taken in for emissions today, it failed Hydrocarbons having 85 PPM while the limit is 53, and failed CO with a .58% where the limit is .28%. NOx was good, 72 out of a max of 614 PPM. As far as I know, the only major mods are a K&N short intake and an SS exhaust. Could it be something simple like a bad sensor? I will have the check engine indicator diagnosed as soon as I can get it into a shop. That might obviously help in trying to figure this out. In the meantime, can anyone guess exactly what could be going on here? Is the oil possibily related to the check engine light and the poor emissions performance? Why did the car fail emissions, only to pass the same day after the owner drove a couple miles somewhere? If anyone has any thoughts on this I would appreciate the input.

Thanks

 

sounds like o me you have a high mileage motor, that someone didn't take care of. I'm guessing you need to place the cats, but I thing I would try doing a full tune-up first and change the oil. Then take it down for a retest.

 

Looks like who ever owned it, failed the test, took it somewhere and either had a buddy pass it for him or tipped off the worker there to pass em.

 

As said above do a full tune up and change the oil so you know what you have. Have the engine light checked out and go from there. It could be just a bad oxygen sensor.

 

I just figured that I could get the OBD I codes myself just by reading the light flashing on the dash. The codes it is registering are 26- Evaporative purge control solenoid circuit: EVAP purge control solenoid circuit is faulty. Check the wiring harness, and code 28- Transmission Range (TR) Check the transmission range control circuit. The evap system consists of the charcoal filled evaporative emissions canister and a control valve. My service manual says to check the canister and replace it if necessary. I'll take a look at it to figure out what is going on. I know it is not the gas cap because I just purchased a new one and I still got the check engine light. I also just bought a new oil filler cap. I'll see if the oil leaking problem goes away or diminishes with this new cap. Some new plugs and wires sounds like a good idea and certainly could not hurt. Anyone have any idea what a transmission range warning would be? I have the six speed gearbox.

 

And yes, it does kind of seem like the guy drove down to his buddy's place and let him pass emissions.

 

or the place that smogged it, fixed something on it, test drove it, then retested...could be a possibility if it wasn't taken to a Test Only Station.

 

You've got the code desciptions wrong. For the correct codes, use the list on Shoebox's website. Be sure to look at the "93" column on the right side - the 93 codes are different from other years in many cases:

http://shbox.com/1/Dtcs.htm

DTC 26:
Quad-Driver Module (QDM) #1 circuit
applies to:
- AIR pump relay circuit
- EGR solenoid
- EVAP solenoid

DTC 28:
Quad-Driver Module (QDM) #3 circuit
applies to:
- fan control relays
- a/c relay

Appears you need to look at a few other systems to determine which one failed and which needs to be serviced/replaced.

The oil leaks at the oil fill cap, at the vent line at the back of the passenger side valve cover (that is not the PCV valve..... its just a plastic elbow to connect the vent line from the throttle body - the PCV valve is on the driver's side of the intake manifold), and at the drivers side valve cover may indicate excessive crankcase pressure. This could be the result of a plugged PCV valve. Check it and make sure its not plugged. Could also be the sign of excessive blowby on the rings. Too much blowby and the system should vent the excess pressure to the throttle body line, which will put oil into the intake air charge.

High HC and high CO, combined with low NOx generally indicates an excessively rich mixture. Misfires, exhaust leaks before the O2 sensors and faulty O2 sensors can contribute to that problem..... not to mention large amouns of oil being sucked into the throttle body. And a saturated EVAP canister can also contribute to a rich condition.

Sounds like a really "tired" engine.

 

Thanks, I would never have know about those specific '93 codes. I think I probably have a vacuum leak at one or more locations. I will look at my PCV valve, all the hoses and the EGR valve.

 

A vacuum leak will make it go lean.....

I would look at doing a tuneup on the car...and also check the evap purge solenoid, if it sticks open the car will show slightly rich, which is what it looks like to me....

 

based on those 'special' '93 engine codes which narrow the faults down to either "it is this specific O2 sensor", or "it could be anything else in your entire engine compartment" (unfortunately, a code 26 on a '93 car tells you absolutely NOTHING), would I see only Electrical faults in the emissions systems? for example, if the evap purge solenoid was malfunctioning, that could vary the signal being sent back to the computer and trip a code. However, if say the EGR valve itself were damaged or not functioning correctly, would that necessarily trip a fault code in the computer on this fairly early diagnostics vehicle where the EGR valve is not as electronically integrated as it might be on a more modern car. would it take an electric component out of the complete EGR system such as a solenoid or valve in order for older computer to register a fault even if there were problems elsewhere in the system?

 

The 93 Quad driver module codes are related strictly to the electrical circuits involved. The ECM is checking the circuits for the AIR pump relay (bad fuse), EGR vacuum solenoid and EVAP purge solenoid. It is also checking the Quad Drive Module itself (a sub component of the ECM).

There is no other function check on the AIR or the EVAP systems in OBD-I. There is a functionality check on the EGR which would set DTC 32 if the PCM does not see the MAP change when it cycles the EGR solenoid, indicating no flow = faulty valve, leaky vacuum lines, stuck solenoid, etc.

AIR, the fan relay and the AC switch are not causing your problem. Its probably running rich. The EGR stuck open, or the EVAP stuck open and pulling on a saturated EVAP canister might make it run rich. You can check the EGR valve fairly easily.... if its wide open at idle the engine would be stalling, if its open a bit, it might just cause a rough idle. You can push the valve open at idle to see how it affects the engine. Your EVAP could be checked simply by pulling a vacuum on the line that goes from the EVAP solenoid to the throttle body. It should not flow air at idle.

 

My friend did manage to open it while idling and it did effect the engine somewhat. Could not get it to open all the way and cause the engine to stall. Would it hurt to try Engine Restorer? I haven't heard anything BAD about it, just exclaimations of "damn, your engine isn't even broken in yet. don't put anything in it." since this engine is most likely pretty worn out as noted by several people, would it hurt to try this? if there are gouges in the cylinder walls, they could be causing a blowby condition, and this product would help in filling those scratches to at least some degree.

 

i love engine restor on my old trucks but im talking 200k and 300k plus miles
i never used it on a car before them

 

As an update to anyone who saw this thread- finally brought it in today. Guy said half the computer was fried. Tested it on two separate diagnostic units with the same result. It had been operating on limp home mode the whole time I've had it (3 weeks). So basically, it needs to get replaced before we know if anything else is wrong. He said that it may not have even been processing the signal from any of the O2 sensors so that would explain any behavior that would look like I had a bad O2 sensor. The guy said he'll try to get a new computer tomorrow. I hope it doesnt cost more than $400 or $500.