UofACATS

I just purchased a well-used 91 LS400, 150K miles. It will idle when given a slight amount of gas, but without will die usually. When floored, the RPMs rise very, very slowly. The car has NO power, and can barely move around. When we were first looking at the car, while idling the cats were glowing red with heat.

It was theorized that the cats were destroyed and clogged, thus no air could escape resulting in the above symptoms. I pulled the front two cats and they looked fine. I started it with the cats off and the poor idle/no power symptoms remain. I checked for codes via the CEL flash method, and none were stored. The CEL is not on either.

Any ideas?

Thanks

PureDrifter

iTrader: (10)

the cats ARE dead, any time they reach the "glowing red hot" stage they are useless. check the maf, and make sure it isnt running rich. also check the o2 sensors. while ur at it check to make sure theres nothing blcoking the exhaust.

UofACATS

Thank you for the response.

First thought about the car was it was probably dead, blocked cats. I suppose the next logical question is can I tell by looking at the cats if they're dead or not?

I looked through the cats and could see a little light if this is revelant. Also, thing is, the poor idle, no rev problems are the same even though the cats are removed and there is no exhaust restriction. Additionally, with compressed air, I pressurized the exhaust through both sides when the cats were previously located, and it travelled through the exhaust out the rear tips.

My thoughts are if the o2 sensors are dead, the the CEL would be on, but maybe not, I've owned the car for 2 days and I don't know how "smart" the computer is.

I pulled the sensor that sits on top of the MAF and it didn't look like it could be cleaned or anything. The connection seems good.

One tech suggested the car was running lean, thus the red hot cats.

RA40

iTrader: (6)

Welcome to CL.

Pull the neg battery terminal and leave it off for 30 seconds to reset the ECU's. (You'll lose seat memory, radio stations etc...) Then start the car and see how it runs. If it still dies, then you'll systematically need to go through checking fuel delivery, ignition to verify function. If a CEL shows, then you have an error code that can be diagnosed.

If that cats are removed, this makes it easier since you know they are having issues.

UofACATS

Thank you, I will do that monday.

19psi

you could be running very rich which would cause a misfire and excessive carbon emissions, which the cats will try to get rid of but won't be able to keep up with. make sure you dont' have any vacuum leaks. if possible, get a scan tool and check the fuel trims.

Balling

or you could be having a timing issue as well. Extremely retarded ignition will cause the same problems you described

UofACATS

[QUOTE=PureDrifter;3072381]check the maf, and make sure it isnt running rich. also check the o2 sensors. [QUOTE]

How do I test these?

UofACATS

[QUOTE=RA40;3073439]..If it still dies, then you'll systematically need to go through checking fuel delivery, ignition to verify function. QUOTE]

How do I test these?

UofACATS

The only scanner I have access to is ODB2. What scan tool should I buy?

Should I have the dealer scan it?



Thanks for the assistance.

PureDrifter

iTrader: (10)

you have an OBDI car (pre 95) so the scanner wont work.

go to Lexls.com and read the tut on reading engine codes.

UofACATS

Thank you!

19psi

the factory scan tool can read and monitor the ecu. you may just want to pay them an hour to diag the car and then you can fix it yourself. it might end up easier and cheaper that way.

LiCelsior

iTrader: (32)

or u can pull the codes from www.lexls.com with a 20cent part and 5minutes of ur time lol.

Dutch

i concur with the whole dead cat thing, the best thing i could reccomend is taking it to the dealership and paying for their diagnosis