Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

94 Marquis "hesitation" 45-55 mph

I have a 1994 Grand Marquis with 123,000 miles on it. Recently I experienced a “hesitation” while passing through 55 mph,

usually "under load " as in going up a small hill. I have had intermittent “check engine”

warning lights in the past and put the car in for a check. One of the O2 sensors was bad

and we changed all of the other “code” sensors as well. EGR ports were cleaned and the transmission was flushed and fluid replaced.

The car still behaves badly and I even experience the hesitation at about 40 mph.

It seems to be ok until the engine heats up

to normal temp. At cruise at 60mph all seems well as does around town at 30 .

My Ford mechanic has no answer and I do not want to spend more money like changing ignition wires etc. (throwing parts at it ,he says).

If you step on the brake just hard enough to light up the brake lights does this nonsense stop?


What does it do if you lock the transmission in third gear?

I have not tried tapping the brake… I have turned off Overdrive but that was no help… I looked at some older "problems " and synchro shudder seemed
to be similar

I was thinking that it might be TC shudder too. I hope they used Mercon V. This is a Ford service department working on it? If you get no more suggestions here, try

The mech that changed the fluid worked for the local Ford agency so I suspect he used the right stuff . I’ll try the crownvic site . Much obliged. I would at least like to get it running good enuf to sell.
Oh yes , I sent the question to CAR TALK but the said they get 500
mails per daY!!!

The car "behaves badly ?’s a teenager after all !

just remember that just because you had the transmission flushed doesn’t mean it isn’t the problem. A lot of times having the trans flushed can actually create more problems since flushing removes the varnish and buildup in the clutch plates inside the trans.

a hesitation at a certain speed could be many other things as well, from a bad spot on the throttle position sensor to weak fuel pressure, to a clogged injector.

have someone test the fuel pressure and make sure that it is within specs.

also may want to have the injectors cleaned. most places will do and injection service for around 30-50 bucks.

Some of this era of Fords were prone to a torque converter shudder that usually occurred around 45 MPH, give or take, when the transmission shifted into Overdrive from 3rd gear.
Changing the fluid to Mercon V often solves the problem but in worst case scenarios the converter is replaced.

This shudder occurs during light to moderate acceleration. If you accelerate firmly and this problem is not there then you know the fluid and/or converter is at fault.

While not necessarily of the opinion that the plug wires are at fault it is something to consider. Some of these wires could be problematic on the earlier 4.6 Ford vehicles and while I don’t remember the details, it seems to me there were about 7 different variants of wires.
You should also check all of the coil terminals and the plug end of the wires for corrosion (a bit hard to do on the latter). I’ve seen a few vehicles that exhibited odd symptoms due to something simple like this. One would think a corroded coil terminal would cause problems at idle and all speeds but it may not be so.

A problem in the EGR system could also do this.

And, you don’t think that it’s a fuel flow/pressure problem because…?

Thanx for all the ideas;; fuel pres was Ok, Egr was cleaned and ALL
"code" sensors (throttle posit etc)were changed.Injectors were cleaned. “Firm” acceleration seems to work but I am also getting some “shudder” at about 40mph… I fear the Torque converter is the problem. Is there an easy fix for that ? Like adjustment?

Have you tried leaving the transmisson selector in Drive, not Overdrive, and noting if the problem goes away? If it does then the fluid and/or converter is probably the culprit.
There is no adjustment on the converter. Ford even issued a Technical Service Bulletin about this problem with the recommendation to change fluid a few times (Mercon V) to see if the problem goes away. In severe cases, the converter must be replaced.

I always change the fluid in my Lincoln about every 30-35k miles but I’ve noted that around the 35k miles mark that sometimes a faint hint of a shudder may appear at times. It’s never been a problem and the transmission still shifts and works like new at over 225k miles so it’s something I don’t even worry about.