: Service engine light



The Noel
12-02-11, 12:53 AM
I just bought a 99 Deville D'elegance from a dealer auction last week and decided to keep it for myself. The car drove very nice, however it would hesitate during idling and would take forever to start sometimes. I had a mechanic check it over and he said all was good except for the fuel pressure regulator. So I bought a new one from the Cadillac delar I used to sell for and installed yesterday. After that my Deville idled perfect and started up with no issues. Today this evening the service engine soon light comes on, but it's still running fine, and starts with no issues. So I go home and pull the codes from the dash display. I get P0171 and P0174. What did I do wrong? Before I changed the part I took off the fuel cap, depressure the fuel rail line, and after replacing the part I did the procedure to pump fuel before starting and running the car. I'm stumped!

RippyPartsDept
12-02-11, 01:08 AM
what are the definitions of those codes?

The Noel
12-02-11, 01:31 AM
P0171 Fuel Trim System Lean Bank 1
P0174 Fuel Trim System Lean Bank 2

iflipcars
12-02-11, 01:33 AM
Lean condtion, bank 1 and 2. Lean conditions are usually caused by a vacuum leak downstream from the MAF sensor, or a dirty MAF sensor. If you have a set of safety torx bits, u can pull the MAF out of the housing and clean the filament that way also ! Safety torx fasteners have a small nipple in the middle that doesn't allow a normal torx to get hold of the screw. I wouldn't recommend it, but I have seen techs use a needle nose vice grip to get the screws out....I would get a set of safety torx bits for the job. Use Brake Clean to clean the MAF btw, not carb cleaner.

An easy way to check for vacuum leaks is with a can of brake clean / carb spray. With the engine idling and the air cleaner still assembled (to reduce overspray from messing up your test) spray the entire intake near where the runners meet the intake, and all the vacuum lines. If the engine begins to rev higher when spraying, u have a vacuum leak !! Don't forget to spray the EGR also.

The Noel
12-02-11, 01:36 AM
Lean condtion, bank 1 and 2. Lean conditions are usually caused by a vacuum leak downstream from the MAF sensor, or a dirty MAF sensor. I looked at the MAF sensor on my 98 N* the other day, and it seems to be one where the filament is hidden from being easily cleaned, but I didn't look at it long. It may be possible. An easy way to check for vacuum leaks is with a can of brake clean / carb spray. With the engine idling and the air cleaner still assembled (to reduce overspray from messing up your test) spray the entire intake near where the runners meat the intake, and all the vacuum lines. If the engine begins to rev higher when spraying, u have a vacuum leak !!

If you have a set of safety torx bits, u can pull the MAF out of the housing and clean the filament that way also ! Safety torx fasteners have a small nipple in the middle that doesn't allow a normal torx to get hold of the screw. I wouldn't recommend it, but I have seen techs use a needle nose vice grip to get the screws out....I would get a set of safety torx bits for the job. Use Brake Clean to clean the MAF btw, not carb cleaner.

I do have the saftey torx bits. It used to own a mercedes v12 and did most of the work on it. I'll try that. I'm just puzzled why that would happen right after replacing the FPR>

Ranger
12-02-11, 01:52 AM
Maybe you knocked a vacuum line loose. Otherwise it is unrelated.

The Noel
12-02-11, 01:59 AM
Maybe you knocked a vacuum line loose. Otherwise it is unrelated.

That's what I'm starting to think I did. I hope you are right. I'll check it in the morning.

The Noel
12-02-11, 04:38 PM
I did the spary test and at by the front right corner of where the intake meets the base the idle stated surging. So I gona go to the Caddie shop and get the intake manifold gaskets, get a new Plenum, (and since I the manifold out) replace the valve behind the power steering pump. Thank you all for your help!

Submariner409
12-02-11, 04:51 PM
Click on my username, open my profile. Two picture albums with a slew of pictures and diagrams of what you'll be getting into. If you're doing the '99 it will be a bit different from the 2000 and later, but the pictures will help.

That intake manifold is a plastic composite - those bolts only take 7.5 ft/lb of torque. Careful............

iflipcars
12-02-11, 09:54 PM
Glad you found problem !! Just noticed I double posted, the 2nd being a "clean up" of the first, DOH !! :)

Ranger
12-02-11, 10:52 PM
I was going to delete one, but noticed that they where different so I left them. Do you want one deleted?

iflipcars
12-02-11, 11:26 PM
Yes, the first one is messed up....please wack it :)