: 91 Deville engine skip

07-19-12, 09:40 AM
I have a 91 Sedan deVille, 85K miles, been meticulously care for since new---always garaged. Recently Service Engine light came on--- EGR sensor needed to be replaced. Also had developed a slight skip. Sensor was replaced, injectors cleaned & dist. cap replaced (don't know why the mechanic replaced the cap), New Bosch platinum plugs (properly gapped) and new wires.
Car still skips..... Use only Shell premuim 93 octane ever used. Never overheated---never had the temp go above normal. No oil leaking detected----no smoke, use about a half a quart topping off between 3000 mile changes. Still love the ar but can't take the skip. Tired of paying the mechanic to guess at what the problem could be. Any ideas?

07-19-12, 10:19 AM
If your engine is a Northstar (Your thread title) it does not have a distributor cap, and Northstars HATE Bosch plugs (don't ask me why; it's black magic).

Here's the correct plug wire routing from coil to plug for the early Northstar.

07-19-12, 10:39 AM
It must have been the coil pack that he replaced----I realized that as soon as I sent the post that there was no distributor cap .... I can't figure it out. I love the car, but this skip is making me crazy.
It's turning into a money-pit just trying to figure out what it could be.

07-19-12, 02:54 PM
The '91 Deville has a 4.9 and should have a distributor.

I'll correct the title and move the thread to the 4.9 forum.

07-20-12, 08:32 AM
Did you clean the EGR tubes under the throttle body? My Deville ran perfect up to 196k with original plug wires and Bosch Platinums. Yours should do the same. It is probably carboned up from too much slow driving and premium fuel. If you don't live in the desert I would run a tank of regular with a bottle of Techron. Keep checking the codes too. MY MAP sensor acted up for months before I finally got a code for it. It ran perfect once I changed it.

the recluse
07-22-12, 09:39 PM
Odd, I ran Bosch Platinum's for about...uhm...20 mins before I ripped them out and put Delco's back in.

Never had good success with them in the 4.9...now for clarity...what kind of skip are we talking about here? any hesitation on take off?

07-22-12, 10:27 PM
I also have had no problems using Bosch plugs :hmm:

07-27-12, 03:44 PM
(Flat tappet engine) + (reduced ZDDP in motor oils) = excessive cam-lobe wear.
Usually at #1 cylinder (the 2 lifters at end of internal oil galley) causing a “skip” or miss that can't be tuned, getting more noticable as the cam lobe flattens.
I think a way to check, other that pulling a valve cover, is to:
Block wheels
Set brakes
Start engine
Put in drive
Rev engine with foot on brakes (powerbrake)
Listen for backfiring.
The traverse engine requires removal to address camshaft replacement.

07-29-12, 12:31 AM
83CADMAN, the 91 4.9L had a roller cam. The intake manifold was changed to stop the leak problem that wiped out cams and lifters.

07-30-12, 08:18 PM
So reduced ZDDP in motor oils have no adverse effect on cam wear????
I think eliminating the possibility of cam problem first, before throwing tons of cash at replacing everything that can be replaced, would be a wise move. Bad cam means big bucks. Cost of a valve cover gasket is small change.

07-31-12, 09:20 AM
Spark plugs were changed, what about the wires? Also, pull the plugs and run a compression test. Could be an injector, get a stethoscope hold it on each injector while engine is idling. Each should sound the same. What is your mpg? I would think he would have changed the rotor when the cap was replaced, sounds odd to me.