WobblySausage

Hi,

I just bought a new to me '95 Z28 Automatic (4L60E AFAIK). I'm currently in the process of making the car reliable, and I was wondering what the cause of these issues may be:
- There are small fluid leaks all over the place. I've had the car for 3 days so I haven't figured out exactly where they're coming from (if multiple places), or what the fluid is yet. I went ahead and picked up an oil pan gasket to be sure, but I haven't installed it yet.

- It's a little slow to turnover when the engine is cold, despite "hot" weather. After the car has been running it starts up pretty quickly.

- Strong fuel smell from the exhaust when running.

- Service light comes on and off intermittently.

- ASR light on, ASR button near center console does not work.

Does anyone have any advice on what/how I should start? My goal is to get the car in a reliable/easily maintainable running shape, before I worry about doing anything fun with it. I'm getting a moving permit for it tomorrow, so my first step after that will be changing the fluids, but I'm honestly a little lost at even how to approach these. I was thinking spark plugs, and spark plug wires just so I know what's in there, and when they went in.

There's also a transmission type of issue which I posted in the appropriate Drivetrain forum.

There is Borla exhaust (I believe the headers are stock) if that makes any difference for the fuel smell. I'd probably like to fix this first, as I'll be driving my baby son around in it with me sometimes.

Thanks for the help if anyone can offer it.

Edit: vvv noted and will do. Thank you.

Injuneer

See my response on your trans post, outlining the need for a scan, and recommending Scan9495.

WobblySausage

Not sure if I should keep both threads going. If not just let me know or close or whatever.

Here are the logs I ended up with:
https://www.dropbox.com/sh/2hulr78du...I1BxyQLKa?dl=0

36kb log is the engine log.

Now I didn't drive around with this on or anything, so idle only readings. However if it matters the battery hasn't been disconnected since I've bought it.

Here are the fault codes as reported by the software:
https://i.imgur.com/SkA571s.png

Some more info: It starts really well in the cold. But in the heat it definitely takes a good 3-5 seconds of starter churning to turn over.

Injuneer

Downloaded and set them up, formatted for review, etc.

Barometer reading appears to indicate you are located at 4,000-ft above sea level. Is this correct?

Even when idling, or when driving, you need to run it at least 206 seconds, for the PCM to transition to closed loop. I'd say do a minimum of 5 minutes for a log. You want it in closed loop to evaluate the A/F ratio control system. The three requirements for closed loop are coolant above ~118*F, O2 sensors active (heated to about 600*F) and the timer from startup timed out (usualy about 206 seconds).

Your Bank 1 (left/drivers side) O2 sensor shows a static reading in the range of 0.453 - 0.457 volts. That indicates an open circuit, confirming DTC 13. Could be the sensor, could be the wiring. Check the harness. One way to test is to swap the two O2 sensors side-to-side and see if the code moves to Bank 2 (DTC 63), indicating a faulty sensor, or stays on Bank 1 indicating a wiring problem.

In addition to the 5 codes you listed in above, in one frame it also shows:

DTC 11 - SES lamp fault

DTC 16 - Loss of low resolution signal from the cam position sensor in the Opti

Those could be just spurious data. I need to look to see if there is any other suspicious data in that frame.

DTC 29 for the AIR pump sets when their is an open or short in the control side of the AIR pump relay. That code usually sets when the fuse for the AIR pump blows. Even if the AIR pump has been deleted, in OBD-1 you will not get a code as long as there is a good fuse in the control circuit. Check fuse #7 in the underhood box.

The AIR pump status flag in the data log shows a request for the AIR pump, so that may be a "stored" code and not an active code. Pull the "PCM BAT" fuse in the underhood box for 30 seconds, restart the engine and see if the code comes back.

DTC 32 indicates the PCM cycled the EGR vacuum solenoid, and there was not the expected change in manifold absolute pressure (MAP). The EGR vacuum solenoid is electrically OK, or that would set code DTC 27, Someone may have deleted the EGR valve, disconnected the vacuum line, there is a leak in the vacuum line, the EGR valve has failed or the EGR vacuum solenoid is plugged up.

DTC 48 indicated the PCM sees that the engine is running, but is not seeing the variable frequency signal from the mass air flow (MAF) sensor. When this happens, the PCM defaults to speed-density mode to calculate the mass air flow into the engine. Might not even notice any difference in operation. Check for +12V on the pink wire at the MAF sensor harness connector (connector off the sensor), check for a solid ground on the black/white wire at the connector. If your multi-meter has a frequency scale, look for a signal around 2,500 Hz at idle, on the yellow wire.

There is a value for mass air flow in the data log, and I don't know if that's an MAF sensor reading, or a calculated value. If it's an MAF sensor reading, your code is "stored" and not "active".

DTC 61 sets when the PCM determines the refrigerant charge is low.

Looking at the rest of the log:

OK:
-MAP sensor, assuming you are at 4,000-ft elevation
-system voltage
-CLT and IAT temp sensors appear to be working and rational
-TPS volts, assuming you blipped the throttle very briefly at about 600 seconds
-spark timing appears stock
-IAC position
-Bank 2 O2 sensor appears to be operating, but it could be evaluated better in closed loop.

Other than the thing mentioned above, don't see any problems. But you need a more complete data log, getting it into closed loop, and then actually driving it on the street.

I don't see any transmission codes, so you need to drive it for that as well. The trans data log would be more meaningful, but I'm not an auto trans expert, so my analysis would be very limited.

FredM

I would start with all essential fluids and filters. I did same thing with my car. Its 20 years old with great paint and interior. But everything else was still 20 years old. Replaced all fluids, filters, sensors and some suspension parts so far. This winter will be all bushings and mounts, mostly worn out rubber parts.

WobblySausage

Thank you. While I parse the information you posted, can you clarify what you mean by closed loop? On a drive with Scan9495 running should I push the car hard, soft, both? How long of a drive should I take?

We are at around 4,400 feet, yes. I also did nudge the throttle a bit during the test.

The transmission is shifting much better after a service (I didn't feel like doing it myself). I believe it was low on fluid. There's a small leak per the technician, but I'll keep an eye on it until I can replace whatever is allowing leaks.

Alright, I believe the only thing left would be a brake fluid change as far as essential fluids.

The interior on my car has a small tear on the driver's side seat. I think that's pretty common based on other used car listing I've seen. I'm going to try to sew it up.

The MAF sensor is expensive, so I probably won't replace that unless I need to. The previous owner installed a CAI so I wouldn't be surprised if something happened on accident with the wires there. I've got 6 days to work on the car next weekend, so I'll be trying the L/R O2 sensor swap as mentioned by Injuneer to see what's going on there. I'll be doing some comprehensive inspections when I get the car on some jack stands next week. I'm not sure what's been replaced yet.

Thanks again. I can't wait to get this car up and running well. Then I can think about getting into some mods beyond trunk/hatch hydraulic shocks.

Anyone have a good recommended book to work on this car, preferably year specific? I'll be doing most things solo so some diagrams would help when I'm working on it.

Injuneer

"Closed loop" means that the PCM is reading the O2 sensors, and adjusting the fuel supply to achieve the target A/F ratio.

The engine starts in "open loop". The PCM ignores the O2 sensors, because they are too cold to work, and their values would indicate very lean, because of the AIR pump forcing air into the exhaust system. The AIR pump helps the O2 sensors heat up faster, by helping to burn the high excess fuel in the exhaust, from the rich A/F mixtures used for cold start. It waits until they are hot enough to produce readings, and then switches to closed loop operation.

When you go wide open throttle, the PCM switches to "power enrichment" mode, and sets a richer target A/F ratio, to produce better HP and torque. Again, the PCM ignores the O2 sensors with regard to adjusting the A/F ratio. They will still set codes if they reach an extreme lean condition. The stock, narrow band O2 sensors are not accurate at the richer A/F ratios required to produce max power and torque. The flag for "closed loop" will remain at "1" in a scan, since the closed loop operation is enabled, even though it is not being used. But there's another flag for PE Mode, and that will switch to "1" when you have hit the right combination of throttle percent and RPM to enabler PE mode.

Shbox.com has a ton of info on the LT1 engine, and 4th Gens in general. Rob (Shoebox) has a 95 Z28, so a lot of his photos and documents are common to the 95. Because of the similarities between the 94 and the 95, the 1994 factory manual will be useful. You can get a free download here (another great effort by GaryDoug):

LINK: 4TH GEN SERVICE MANUALS; 82-02 PARTS DIAG; 99-02 WIRING DIAG - Fourth Generation Pontiac Firebird (1993 - 2002) - Firebird Nation

Shoebox also has a link to downloads of the year specific Owner's Manuals, if your car did not come with one.

A great book for engine specific issues:


An interesting article:

Rebuilding the Chevrolet LT1 Engine, Doug Anderson, Automotive Rebuilder, September 1999

And most of the info on this site is correct, although there are a few errors:

4th Generation (1993 - Present)

I should really just "sticky" this list sometime.