: 99 SLS runs funny



goinbig78
12-26-06, 05:26 PM
I have a 1999 SLS and in the last month or so performance has been steadily decreasing. I have noticed that at times that the car would seem to hesitate as if the motor was about to die (especially under load). Recently it has started to backfire.

I changed the fuel filter as the problem seemed to mimick a vehicle running out of gas but this had no effect.

Please help.

Ranger
12-26-06, 05:51 PM
Start by pulling the codes. Then check fuel pressure and FPR.

eldorado1
12-26-06, 06:02 PM
Second the fuel pressure check

Sounds suspiciously like a fuel pump problem, but could just as easily be a sensor (MAP or TPS...)

STS127
12-26-06, 06:13 PM
Try a tune-up. Plugs, maybe clean throttle body or run a fuel system cleaner like 44K or Techron.

goinbig78
12-26-06, 06:17 PM
Honestly ive never done any serious work on this car. I have done all the work on my cars but am not familiar with the Northstars.

Do I need any specific tools for the pressure test?

Ranger
12-26-06, 06:36 PM
Just a fuel pressure guage. The tap is on the fuel rail. Looks like a tire valve. Use a guage with a long hose and tape it to the windshield. Watch the pressure when you drive and see what it does under the conditions that cause the problem. If pressure falls greatly when you throttle up, the pump is going south.

dp102288
12-27-06, 03:22 PM
goinbig78, were you able to pull the codes?

goinbig78
12-28-06, 04:18 PM
My sisters boyfriend claims to have gotten no coes on his scanner. If it trully is not throwing a code then what next.

Ranger
12-28-06, 05:11 PM
See post #2. If that is OK, then it's probably time for plugs & wires (A/C Delco).

clarkz71
12-28-06, 05:21 PM
AC Delco wires # 748N, AC Delco plugs 41-950.

goinbig78
12-28-06, 05:37 PM
How do I test the FPR

eldorado1
12-28-06, 09:44 PM
http://www.cadillacforums.com/forums/cadillac-tech-tips/61600-how-check-faulty-fpr-fuel-pressure.html

dp102288
12-28-06, 09:50 PM
^^ This thread has good info

There is also a good thread on the FPR in the Seville/Eldorado sub-forum.

goinbig78
01-02-07, 04:24 PM
Ok, I checked the FPR and noticed no fuel around the vaccum line so based on the great spreads regarding this, there is no problem. So once again we hooked up the scanner and did a KOEO test and got no codes. I then hooked up a fuel pressure guage and the while in idle the guage bounced between 40 and 46 psi, the same happend when the vehicle was put in drive and the rpms brought up. The car even hickuped just as it has been doing and the guage did not fluctuate.

Im at a loss. Ive had fouled plugs on other vehicles but never had symptoms similar to these so I am scepticle to think it is plug related. If its throwing no codes, FPR seems good, and fuel pressure seems ok then what do I do next.

eldorado1
01-02-07, 04:49 PM
I would use the "dash scanner" vs some storebought unit, just in case. It should at least have some history codes. This is a case where "no news" really is "bad news".

goinbig78
01-02-07, 05:09 PM
Youll have to forgive me but what is a "Dash Scanner" vs. "store Bought"

Ranger
01-02-07, 05:15 PM
Ok, I checked the FPR and noticed no fuel around the vaccum line so based on the great spreads regarding this, there is no problem. So once again we hooked up the scanner and did a KOEO test and got no codes. I then hooked up a fuel pressure guage and the while in idle the guage bounced between 40 and 46 psi, the same happend when the vehicle was put in drive and the rpms brought up. The car even hickuped just as it has been doing and the guage did not fluctuate.

Im at a loss. Ive had fouled plugs on other vehicles but never had symptoms similar to these so I am scepticle to think it is plug related. If its throwing no codes, FPR seems good, and fuel pressure seems ok then what do I do next.
Change the plugs & wires. Get them from http://www.rockauto.com. See post #10.

eldorado1
01-02-07, 05:53 PM
Youll have to forgive me but what is a "Dash Scanner" vs. "store Bought"

http://www.cadillacforums.com/forums/cadillac-tech-tips/55172-how-pull-codes-got-codes-warning.html

goinbig78
01-03-07, 10:47 PM
It gave me codes. Here they are, what do they mean?


P0603 - Control Module Long Term Memory Reset
P1520 - Transmission Range Switch Circuit
P1527 - Transmission Range to Pressure Switch Correlation

eldorado1
01-03-07, 11:27 PM
There are two sets of switches in/on your transmission. There's a box sitting on top, and a set of pressure switches inside. What your codes are saying, is that they don't match. When one says you're in drive, the other says you're in 3rd (for example)

Probably just means it needs adjustment, and isn't a big deal. The long term memory just means the computer was reset (codes cleared).

Keep driving it, and try to get it to act up. All you need is one code to help point the way, and it doesn't look like you have it yet. It seems like it should set a misfire code if it's running as bad as you say it is.

goinbig78
01-04-07, 12:23 AM
Thanks a lot for your help. I drove it around this morning and as soon as I put it in reverse it felt like it was trying to accelerate down the driveway in short bursts.

After running another scan I got P1520 - (Transmission Purge Circuit) and U1064 - (Loss of ccommunication with DIM)

It seems to me that the problem is this purge circuit. Is this something that can be fixed easily?

goinbig78
01-10-07, 12:59 PM
Im desperate, can anybody help

Cad tech
01-10-07, 04:31 PM
Dont worry about the p1520 they always set with external PRNDL and will not set cel, ses light it usally runs in conjunction with p1527 . This vehicle uses an electronic gear indicator display. There are four inputs which are switches to ground that each have a unique switch pattern. All four of these inputs are housed and operate together in the Transaxle Range Switch. The PCM uses the combination of the switch patterns to determine the gear selected by the driver. This information is then sent by serial data to the IPC for gear indicator display. This diagnostic test monitors the transaxle range switch for false outputs. The DTC will set if: the transaxle range switch is indicating a gear that the PCM does not recognize or the transaxle range switch input does not match the input of the transaxle pressure switch. That is not your problem...Power brake the vehicle and see if there is a misfire...if there is thats your problem and without a tech2 you will not be able to tell which cyclinder it is......So as the others had said check your spark plugs checke for gap and condition they should be platinum tipped 41-950 (ac)if they are not AC Delcos change them any way....alsocheck for carbon scoring (a black tracer on plug Shaft) if the tracer is there replace wires and plugs. check this then post back with findings.............

clarkz71
01-10-07, 04:39 PM
AC Delco wires # 748N, AC Delco plugs 41-950.


Like Ranger & I said 12 days ago.........:yup:

goinbig78
01-10-07, 05:08 PM
Should have just listened I guess, ill do that this weekend and see what changes there are.

Thanks for all your input guys.

clarkz71
01-10-07, 05:10 PM
Good luck and let us know what happens.

eldorado1
01-10-07, 08:29 PM
Tested the fuel pressure already?

goinbig78
01-18-07, 12:45 PM
Ok I replaced all the plugs and checked the plug wires and the problem is still there. It seems to be a little better now but I really notice the problem as soon as I start to drive up hill.

I checked the fuel pressure but do not have a hose long enough to check it while I drive so I had to do it at idle then in gear and it staye at 40-45 psi.

What now?

Cad tech
01-18-07, 04:54 PM
lightly mist the coil pack assm with water, while it is running,check for arcing on coil packs. if you can get a hold of a tech2 try a injector leakdown test...

clarkz71
01-21-07, 01:10 PM
Ok I replaced all the plugs and checked the plug wires and the problem is still there. It seems to be a little better now but I really notice the problem as soon as I start to drive up hill.
What now?

I thought you were going to replace the wires.