Hi all. I just replaced the cat, y-pipe, and exhaust manifolds on an original 94 Z28. The car ran sluggish before the cat replacement but it indeed runs better now. It is very sluggish when pulling out, but after that it seems fine. It feels like it is being held back.

It is the original engine with 189K miles and I reused the O2 sensors swapped from the original exhaust manifolds. It seems to rev fine but pulling out is a chore.

Any thoughts or suggestions?

Thanks in advance,

Greg

 

Have you checked the fuel pressure?

Have you scanned it for codes?

Any evidence of misfires?

 

a quick question.. you have a muffler on it?

 

No, I haven't checked the fuel pressure. It revs fine, it just struggles pulling out. Sorry, I'm new this "modern technology". Do I need a scanner to get the codes, or do I look for a repeating set of flashing lights? No misfires.

Thanks for the ideas.

I like the fuel pressure idea. I'll pursue that first and check into how to scan for codes.

Could the O2 sensors possibly cause these symptoms?

Greg

 

Yeah, new cat hooked to original mufflers. You thinkin' clogged muffler?

Thanks,

Greg

 

nope, when i first got my car, the redneck who owned it previously didnt have a muffler on it, the car had absolutely no bottom end.. i put a muffler on it and it helped alot..

 

do you own a laptop?

if your planning on keeping the car, you can gain alot of self help by purchasing an aldl cable, and getting freescan..
its free ,it reads codes/datalogs/monitors.... its well worth the $60 for the aldl cable..

my car is an auto with 2.73 gears, it was a dog out of the hole before i added the stall, it still needs gears bad...

 

93 was the last year you could flash the codes on the SES light by shorting the ALDL pins. You need a "real" OBD-I scanner - and not the $30 Actron "code reader" that says it works on 94's but will not, its just a switch that shorts the ALDL pins. Actron and Auto XRay make real OBD-I scanners, and some of the newer OBD-II scaners also include the capability to read OBD-I as well.

FreeScan, mentioned above is good for data logging, as it TTS DataMaster:

http://www.ttspowersystems.com/

 

Have you replaced the spark plugs? Maybe starting to foul.

 

Thanks, I'll do some research and check this out.

Greg

 

If you have any service records on the car it would be worth your time to look into how old the ignition components are. Might be time for new plugs, wires, and distributor.

 

Awesome information! Thanks. I will do a search on this site's sources and the site you listed and see what I can come up with.

Greg

 

Yeah, I forgot to mention that I also replaced the plugs with NGK TR55s while I had the exhaust manifolds off. Actually, none of the old plugs looked fouled or anything.

I've seen references to the optispark being a problem. Can a bad one cause this sluggishness?

Sorry for the newbie questions, I plan to do some more research today and see what sort of symptoms and resolutions I can find.

Thanks,

Greg

 

I did replace the plugs but not the wires.........I should have done this while I had the thing apart.

I will look into the distributor (is this the optispark?).

Thanks,

Just call me newbie Greg

 

Yes... the Optispark is the distributor. The front half has the conventional high voltage spark distribution - cap and rotor. The back half includes an electronic optical pickup for cam position. It sends cam position to the PCM so the PCM can time the spark and the sequential fuel injection. If you have a problem with the optical cam position sensor, it will set codes... but those codes don't turn on the SES light, so you don't know they are there unless you scan it. If the cap/rotor has issues - moisture, carbon tracking, burned contacts, etc. it will not set any codes. It will be down on power and will typically misfire. The 96/97 cars have misfire detection via OBD-II and the added crank position sensor, but the 93-95 OBD-I cars do not include misfire detection.

A missing muffler should not reduce power or torque on a fuel injected engine. In effect, what you are saying about the lack of a muffler causing it to have "no bottom end" might be true on a carb engine, where the improved volumetric efficieny has not been addressed by rejetting the carb. But on an EFI engine, the PCM is fully capable of adjusting for improved breathing (VE). In effect, if lack of a muffler cost bottom end, opening a cutout would be a disaster. It isn't.