View Full Version : 94 SLS back cyls spark, don't fire, smoke

94 SLS
05-03-07, 10:55 PM
I have a 94 SLS with 138,000 miles and a 4.6. To start it, the gas pedal has to be put down an inch or so. After a few seconds it starts and kind of putt putts. There is some black smoke that is noticeable at first. After a minute or two, and especially if you get on it, it pumps white smoke. The back four cylinders have spark to the spark plugs, but if each plug wire is pulled, there is no difference in the sound or performance. The 1,3,5,7 spark plugs are wet and white(new) when removed. The front 4 are dry and car stalls when plug wires are removed. At idle it is hard to rev up. It will barely drive and feels like it has a governor set at 10mph. I checked the injectors and the fuel pressure regulator for leakage three different times, but couldn't see any. The code is 034, the map sensor, which was just replaced by the previous owner, who also just replaced the intake gasket. I noticed a tiny bubble on the map sensor, not sure if this is ok or not. The code went to history for a couple of days, but did not improve performance. Little help please? Thanks.

05-04-07, 12:12 PM
Do you have the spark plug wires on the right cylinders?

94 SLS
05-04-07, 12:42 PM
Thank you for the reply. I have double checked that the wires are on the right coil twice, but because you said that, I am wondering if the last guy switched the coil packs. They are numbered starting at the passenger side, 6/7 4/1 8/3 5/2. I am looking in a manual and It looks like it should be 5/2 3/8 1/4 7/6. It looks like the coil pack is upside down. I will switch it and get back to you. Thank you.

94 SLS
05-04-07, 01:16 PM
After looking at it, it doesn't just switch and I was looking at the 4.9 coil pack picture (can't find one for 4.6). One thing I noticed when I pulled the plugs on the end of the coil pack is that all the prongs are there but 3 of the metal clips that attach to the prongs are missing. That looks of interest. I see that the firing order is 12734568 How does that relate to the coil positions?

05-04-07, 07:32 PM
I also have a 94 SLS, N* VIN Y, Firing order is 12734568. Coil positions starting from the left are Coil #1 6-7, Coil #2 4-1, Coil#3 8-3, Coil#4 2-5.
Even cylinders are in the front 2,4,6,8, left to right, rear is 1,3,5,7 left to right.
The coil mounting plate should have 2 wire prongs in the front for each coil pack. If all of this is correct on your car check the injector wiring from the fuel rail to the main wiring harness connector. May particular attention at the point where it bends around the water housing, I had several wires that fuzed together and caused the #1 & #3 injectors to remain open causing bellows of white smoke and horrible fuel economy.
Good Luck !!

94 SLS
05-04-07, 10:01 PM
Thanks for that info. I will look closely at the wiring from the fuel rail.

94 SLS
06-06-07, 12:06 PM
I checked the wiring in the fuel rail but it was all fine. One of the injectors was loose and dangling, so I popped it back in. (after starting didn't seem to help much, less fuel out the exhaust but still smokes and no power) I bought a noid light set and put the light in various injector clips, it didn't light up. Another thing, when the car is turned to the on position, I don't hear it energize. It doesn't make a sound to fill up the fuel rail. The fuel pump regulator and the injectors don't leak, but I don't hear any noise. Is it the fuel pump? The car barely moves in drive and to start it I have to put the pedal half way down. There are no codes and no service engine soon light. Any ideas?

06-06-07, 12:18 PM
What was the very last thing you did when this all started?

94 SLS
06-06-07, 01:02 PM
I bought a project car. The guy put a new intake on it as it was leaking oil. He couldn't get it started. I made that much progress( ha ha). I checked the fuel fuse and relay( I switched it with another), they seem to be fine. I listened in the gas tank and I could hear a motor for a couple of seconds. I started it and it ran better, idled by itself, but after a couple of minutes it smokes bad.

94 SLS
06-06-07, 04:06 PM
The noid light does not come on, so there is some problem between the computer and the injector, what are some of the things it could be?

94 SLS
06-10-07, 09:37 AM
The noid light does come on, I didn't know you had to try to start it to make it work. I put a new FPR on it, but haven't been able to start it, as now all plugs are wet. I'll keep me posted.

94 SLS
06-12-07, 11:55 PM
It turns over hard and it doesn't fire or start. It seems like the timing is off, but you can't use a timing light on the 4.6 right?

06-13-07, 09:44 AM
Timing is set by the PCM I believe. Do you have spark at the plugs?

94 SLS
06-14-07, 12:33 PM
It has spark at the spark plugs. When I let it sit for a day and try to start it, it starts to fire and then backfires.

06-14-07, 01:46 PM
I went back and reread this thread from the beginning. You never mentioned checking the fuel pressure. Has that been done?

94 SLS
06-14-07, 09:24 PM
No, I haven't done that. I called the parts store to get the price on the tester. I read in the manual about it, but it isn't specific about the 4.6. It says to start it and check to see if the pressure changes. How do you start it and check it? I know you are not supposed to try to start it with the intake cover off. Do you think the fuel pump might be pumping too much gas through the FPR and cause it to dump extra fuel in the cyllinders?

06-14-07, 09:59 PM
No I was thinking just the opposite. Too little fuel pressure. There is a schreader valve on the fuel rail (outside of the manifold). That is where you screw the pressure gauge onto to get a pressure reading.

94 SLS
06-14-07, 10:06 PM
Thank you, I will look for the valve, and hope to check it within a few days.

06-14-07, 11:32 PM
It looks just like a tire valve.

94 SLS
06-15-07, 09:08 PM
Thanks Ranger. I tested the fuel pressure and it went to 44 psi and then down to zero in just a couple of seconds. I lifted up the fuel rail and it is leaking, it looks like it is from the black tubing itself. Can I get that repaired or do I have to find another fuel rail? Thanks for the help.

06-15-07, 09:33 PM
I would not try to repair it. Replacement is the best way to go since it holds aprox. 45 psi.

94 SLS
07-26-07, 09:53 AM
I put a different fuel rail on. It now holds fuel pressure over 40lbs, but it won't start. If I let it sit for a day, it starts for about 2 seconds and then quits. It turns over but won't fire. I put a new camshaft sensor in but that did not change anything. Any ideas?

07-28-07, 12:02 PM
Several ideas.

The injectors are split electronically, there are two fuses, check those fuses.

There is a recall on certain years with the black plastic tubing. Check on that because if it's covered it's on ongoing safety recall. I don't remember what years.

The insulation on the wires in the loom to the intake can flake off. It's hidden by the plastic tube covering it. This is the loom running from a connector under the throttle body to the intake. Take the electrical tape off the ends and pull the plastic tube off. It's split to come off. See if any of the wires are exposed and shorted. This happened to my brother and a few other times on the board. It gave a similar symptom to what you have.

94 SLS
07-28-07, 03:38 PM
Thanks for the suggestions. I will check the fuses again. I called a dealer and he said they had a recall on the 95 model, I will check again about the 94. I will look for the loom and check the wires. Thanks.

07-28-07, 05:31 PM
If the fuel rail is external it's a recall. If internal it's not. It's safety in case of fire.

07-29-07, 11:11 PM
The fuel rail recall was for '95 - '97.

07-30-07, 02:37 AM
Thanks Ranger...that's why we keep you around!

07-30-07, 08:24 PM