90 Town Car - stuttering at highway speeds under throttle

[drhill]

Hi Everyone! Got an interesting issue with my 90 Town Car - don't know if its transmission or engine related. If I'm on the freeway going 60 or more the Town Car seems to stutter while accelerating or even just keeping speed. I've tested it and it happens in 3rd and 4th gears. Does not do this around town at all that I can tell. I just put in a new fuel pump recently but I think it even did it a little bit before this.

Any ideas?

Thanks!

[DerekTheGreat]

Hmm. Check the basics, fuel pressure, timing, plugs, wires, fuel filter. Is it a MAF equipped car?

Describe this stutter of which you speak; is it a shudder? Does it feel like the engine is missing?

[drhill]

Hmm. Check the basics, fuel pressure, timing, plugs, wires, fuel filter. Is it a MAF equipped car?

Describe this stutter of which you speak; is it a shudder? Does it feel like the engine is missing?

Ok. Not so much a "shudder" as it is a light back and forth motion. it is like it's running out a fuel a little bit...or as if the the tranny was slipping a bit and grabbing again rapidly.

It is a MAF car. both MAF and Fuel Pump have been replaced in the last year. Both rectified obvious major problems (no fuel pressure - fuel pump fixed it, and maf was verified dead, plugged in new one and it was running perfectly).

[sly]

Most likely an ignition issue (misfire). The AOD does not use a clutch style torque converter like the AODE/4R7X, so it can't be the shudder issue. It could however be worn clutches in the transmission itself when it shifts into 3-4 and it's having trouble holding the gears, but I would definitely lean on ignition issues first as that's almost always the case. Check for loose/damaged wires, timing, and the usual top end tune-up stuff (plugs/wires/cap/rotor). Since it doesn't do it in 1-2, the shock that you're feeling is probably being absorbed by the torque converter. When it shifts into 4 (OD) the torque converter is totally out of the equation (it's still partially used in 3rd from what I've been told) and you feel ANYTHING wrong with the engine. Since it's a MAF car, check for vacuum leaks and leaks in the intake hose behind the MAF as that could lead to a slight lean condition that could cause the misfire.

[Tiggie]

Mine does this every 15k miles - spark plugs in my case. May be worth checking on yours.

And 15k is not normal - mines just a very worn engine that dirties its plugs quickly.

[drhill]

thanks for the advice guys - I'll check out all the ignition parts and replace the plugs if they aren't sparkling clean.

[89TownCar]

'90 Town Cars were MAF? I thought they were speed density still.

[drhill]

'90 Town Cars were MAF? I thought they were speed density still.

I think california cars only got the maf...

[gadget73]

Cali car most likely. 49 state were speed density.

Another possible is EGR problems. I had issues with the regulator on mine and it was going full open when it shouldn't be. It cleared up over about 55 but it surged and ran stupidly below that. Unhooking the green line from the EGR valve stopped it.

Just a thought for another quick check if the ignition stuff comes out as being fine.

[drhill]

well, plugs electrodes were white...i think that means lean...i did have a slowly dying fuel pump for a while so that makes sense. Gap also seems a little wide. Replacing the plugs today. Also, cleaned up the cap and rotor with a little sandpaper, everything looks good. Also found some moisture must have gotten into the coil wire plug on top of the coil...pretty rusty under there. Replaced the coil wire and sanded down the plug on the coil. So far it seems better...hopefully the plugs will make it even better. Then i have to find a long high speed hill to climb to test it!

[gadget73]

EFI plugs tend to run pretty close to white, or extremely light tan. You may be fine there.

[BigMikeIT]

Ok. Not so much a "shudder" as it is a light back and forth motion. it is like it's running out a fuel a little bit...or as if the the tranny was slipping a bit and grabbing again rapidly.

It is a MAF car. both MAF and Fuel Pump have been replaced in the last year. Both rectified obvious major problems (no fuel pressure - fuel pump fixed it, and maf was verified dead, plugged in new one and it was running perfectly).

I recall that same feeling on my car. Like a quick iteration of a two beats a few times. Tad-dah,tad-dah,tad-dah.
Tightening the pan on the transmission helped.

[drhill]

Well, after checking all of the ignition components, i had the rusty coil terminal i fixed and cleaned up the cap and rotor a bit and I replaced the spark plugs. Most were ok but the rearmost plug on each side had some oil on the electrodes and one of them even was bridged to the tip with oil crud....looks like I found my miss fire!

And I found where that pesky oil leak was coming from - valve covers! So now it runs like a top, i'll probably replace the back two plugs again once I get around to replacing the valve cover gaskets. I can't remember if you have to pull the upper intake to do these? It looks like it but I can't remember...

[87gtVIC]

To replace valve cover gaskets you will have to remove the upper intake.

Throttle linkages prevent you from removing the valve cover on the drivers side and the actual upper intake plenum blocks removal of the passengers side valve cover.