marlar98

Good evening.

I'm in a particular vehicle in my area, but I don't know much about Chevys. I've even an Oldsmobile man for many years, but recently I've come across a 94 Camaro z28. It runs fair but rich. According to the owner, he says on cold start it will run fine for a few minutes but shortly after that it starts to hesitate and sputter but maybe after 15 or 20 min of running the check engine light will come on and it will run fine. He's changed the spark plugs and wires the opti egr valve and the coolant temp sensor but other than that, he hasn't replaced anything else.

It has the typical bolt ons, K&N CAI, air foil, elbow, headers, cat-back exhaust. The hesitation and running rich issue happened a month ago according to the owner. The car is priced fairly IMO, but I'd like to get an idea of what could be the issue from those who are more familiar with these cars. I appreciate your input.

Thanks.

Injuneer

At any point has anyone scanned it for codes? That's a lot of money to invest in parts replacement without doing some diagnostics.

Surprised he didn't replace the O2 sensors as part of playing "parts replacement roulette". Would seem to be the likely source of the problem. But don't just start playing his game. Scan it for codes.

You will need an actual OBD-1 scanner. Unlike the 93 LT1, you can't flash the codes on the SES light by shorting the pins in the ALDL connector for 94 and newer. An older Auto X-ray scanner works best. The Innova dual OBD-1/OBD-2 scanners will not work.

An even better alternative is free Scan9495 software, get a cable, and run a data log of the PCM from cold start, through warmup, and a few miles of normal driving. The are a couple of us who can interpret the data log for you.

See the Scan9495 "sticky" thread at the top of the "computer diagnostic....." Forum.

marlar98

Thanks for your input. I thought about the O2 sensor as well when he told me everything he's already done. I'll look into the scan9495 thread.

marlar98

Well I pulled the trigger and purchased the car, and I couldn't be any happier. It's still running a little rich, but it runs 10x better than Saturday when my brother and I test drove it. On Saturday it bogged quite a bit and would barely spin the tires. So I asked the guy a few more questions between yesterday and today. He was putting 87 & 89 octane in it. On the way home, I actually ran out of gas. I went to the gas station and filled it up with premium gas and a can of seafoam. Seemed like after a couple of minutes of letting the car run the idle noticeably smoothed out. The car ran SO much better.

On top of that, the guy has a K&N cold air intake, I noticed he didn't have an air filter on it. After I exchanged funds with the guy, I asked him how long has he been running the car without an air filter. He said he didn't know the air filter was missing. I immediately went to the parts store and put a K&N replacement filter on it.

I'm sure with all the misuse and poor maintenance I'm going to need clean or replace the mass air filter and possibly fuel filter. The oil looked pretty dark so that's getting done also. I added a half can of seafoam to the crank case and will add the other to the intake through the brake booster vacuum line. Anything else I should consider?

Thanks

With

Injuneer

Every fluid in the car should be changed - oil, trans, differential, coolant and brake fluid.

Replace PCV valve.

You've already identified the filters.

Don't let it run out of gas again. Can cause sudden death of the fuel pump.

Get as much grime as you can off the engine. Do not use a high pressure spray, and do not get the Optispark distributor wet.

Check the harness connector for the MAP sensor - they dry out and crumble.

Check the vacuum lines for leaks - the lines are brittle and can crack at the age of these cars. There should be an emissions routing diagram on the radiator top cover/support.

I would still run a Scan9495 data log. There are a couple of us that can help you interpret it. Important to verify all sensors are reading and responding correctly. O2 sensors can be a problem with high mileage. The data log will tell us if the A/F ratio is correct, and how much adjustment the PCM is having to make based on O2 sensor feedback to keep it there.

Check all suspension components for worn bushings and damage.

Check brake pads and rotors.

Verify all dash lights are working. If you don't have an Owner's Manual, go here:

1993-2002 F-body Owner's Manuals

You can also get a download of the factory 1994 shop manual:

LINK: 4TH GEN SERVICE MANUALS - Firebird Nation

If you are not familiar with the details of the LT1, and some of the other features of the car, Shoebox's website has most of what you need:

4th Gen LT1 F-Body Tech Aids

Some insight into the history of the 4th Gens:

4th Generation (1993 - Present)

Some fairly old, but still valid dyno tests of modifications:

WS6.COM LT1 Trans Am

If you want info on your specific car - production date, all options (RPO), and what each RPO code means, go here (used to be free, now I think they charge you $5 for up to 4 lookups):

Comprehensive Chevrolet VIN Decoder

Good luck!!

marlar98

Wow Injuneer! Thanks for the info.

Injuneer

A caution on the fuel gauge - the calibration is terrible. Full, the needle will be above "F" and hang there for about 2 gallons. Tank holds 15.5 gallons. When the gauge reads "1/2" you only have about 6 gallons left. When it reads "1/4" you may only have 2 gallons or less left.

Shoebox has a good article on the fuel gauge in his "how to" page.

marlar98

Thanks for the heads up. My brother and I found out the hard way lol

WS6_Keith

Well, I'm glad to see some people are still getting use out of the old dyno runs from back in the day. I suppose it validates why I keep the site up and running, even though the car has been on jack stands since 2000.

I really hope to get back to that thing in the next few years.

Injuneer

I saw your name on the topic listings, and couldn't believe it... a voice from the past. Good to hear you still have the WS6, even if it's on blocks. My Formula has been unused for about 5 years, and hasn't been to the track in 10 years.

Yes, people still use your dyno info, and I like to post a link to the cracked cross-drilled brake rotors/cryo once in a while.

WS6_Keith

Good to see you're still out there too Fred. I still have my dreams of a twin turbo, 1000+rwhp play toy. One day it might happen. The longer I wait, the easier and cheaper it seems to be able to put one together. Haha.