Diagnosic Assistance Requested -- Hesitation

[DriverSideImpact98]

I went through the entire engine bay looking for potential vacuum leaks when I first noticed this problem, but I'll check the T on the back of the intake manifold -- I don't think I specifically checked that.

That's a good point about the check engine light. To be honest, I don't remember for sure if it's coming on or not. I'll have to make sure to check for that next time I go out there.

One thing that might be messing me up is that since I put the new battery in, I've been disconnecting the battery after I shut the car off so the battery won't discharge (since I only typically start the car every two weeks).

However, maybe that's part of the problem. Maybe I need to leave it hooked up and drive it around a few times so the computer will recalibrate itself (?????). I don't even know if that is realistic or possible -- it's just an uneducated guess on my part.

Anyhow, thanks very much for the input -- it's greatly appreciated. Please keep the suggestions coming if you think of anything else. Meanwhile, as I have the time, I'll gradually try things that you guys suggest in order to narrow it down.

If it was a vacuum leak, it would run crappy all the time. However, its only on acceleration correct? I'm still guessing the cat. Along with needing a general tune up.

But yes, the computer does need to go through a few cycles, which includes certain speeds, temperatures, etc. needing to be reached. And after 10-15 minutes of the battery being disconnected the computer will reset.

[TomO]

If it was a vacuum leak, it would run crappy all the time. However, its only on acceleration correct? I'm still guessing the cat. Along with needing a general tune up.

But yes, the computer does need to go through a few cycles, which includes certain speeds, temperatures, etc. needing to be reached. And after 10-15 minutes of the battery being disconnected the computer will reset.

Been real busy with stuff and just got a chance to check back.

Yeah, a bad cat sounds plausible, but on the other hand, the engine will rev up with no problem (except for the missing when you first open the throttle). My intuition tells me that if a cat were plugged you would notice at least some resistance to revving as the exhaust pressure builds up in front of the plugged cat. This doesn't seem to be the case.

As far as the "T" goes -- I thoroughly checked the engine bay and there is no "T" on the PCV system. There is one line that goes from one valve cover up to the intake and a second line that goes from the other valve cover to another place on the intake (can't remember exactly where -- it's been a long time since I looked). I can't hear or see any evidence of any type of vacuum leak -- I checked pretty thoroughly, but I'm not an expert.

The thing I'm banking on at the moment is that perhaps it needs new plugs and/or plug wires. I pulled one plug and it looked pretty worn. I need to find time to change them out and see if it works.

I recently (about two months ago) changed out the plugs on my '89 Grand Marquis and it made a world of difference. On the '89 I didn't have the symptoms of the '97, which is the subject of this thread, but I was getting some bucking and missing under heavy load at low speed. Changing the plugs completely cleared that up.

[TomO]

I forgot to mention that the "check engine" light does not come on. But, that might be due to the fact that I have not driven the car. (??) The car is not registered at the moment, so I can't drive it far, but I can drive it around the parking lot of the storage area, I suppose.

[BigMerc96]

Clean the MAF sensor. My car did exactly the same thing when I bought it after it had been sitting for 3 years. It eventually threw a lean code on both banks, which lead me to the MAF. After cleaning the MAF and resetting the computer, the hesitation, bogging, weird shifting, etc.. all went away.

[BigMerc96]

Also, there is no vacuum "T" on the '96+ intake setup. '92-'95 have said vacuum "T", along with the older style all-aluminum intake and all the faults that go along with that.

[TomO]

Clean the MAF sensor. My car did exactly the same thing when I bought it after it had been sitting for 3 years. It eventually threw a lean code on both banks, which lead me to the MAF. After cleaning the MAF and resetting the computer, the hesitation, bogging, weird shifting, etc.. all went away.

Thanks for the info. I'll try that. I'm assuming that the MAF is the unit in the intake pipe near the air filter(??) Also, what is the best way to clean it? Thanks.

[sly]

MAF cleaner or contact cleaner. just hose it out in the little hole (don't poke the straw actually inside the hole though). a couple quick squirts should do it if it's not real dirty.

[TomO]

Finally got some time to mess with this. Here's what I've done so far:

1) pumped out almost all the gas, put about 6 gallons of new gas with appropriate amount of Sta-Bil for long term storage -- no difference;

2) put some Sea Foam gas treatment/fuel injector cleaner in the tank -- no difference;

3) installed brand new Autolite double platinum spark plugs, gap set to 0.052-0.054 (old plugs were pretty worn -- gap was between 0.065 and 0.075) -- now runs worse, with same hesitation, but now at idle I'm pretty sure I'm getting an engine misfire.

My suspicion now is that the problem is electrical. I suppose my next move would be to replace the plug wires. I'm not savvy on the newer 4.6 motors. I've heard of the "coil-on-plug" but I don't know what it is. Is that integral with the plug wires?

I forgot to mention -- still no check engine light, which seems strange. But, then again, I can't drive the car except around the storage lot b/c it's not licensed.

[TomO]

I replaced the plug wires and still had the problem, but seemed to run a bit better. I bought a temporary registration and took the car out on the road and drove it around and it seemed to get gradually better. So, I kept driving it -- the more I drove it, the better it ran. I guess it must have been clogged injectors. I guess the new plugs and wires probably helped a bit too.

[Mil1ion]

http://troubleshootmyvehicle.com/ford/4.6L-5.4L/how-to-test-the-coil-packs-1