'94 misfiring - need input

[12valve@heart]

Hope all had a Merry Christmas. I'm a noobie to this forum and to SHOs in general. A couple months ago we purchased a '94 SHO Automatic that had the 60K maintenance done about 5K ago.

In the last couple weeks, the car has started to misfire intermittently. By that I mean that sometimes it will run perfectly but then suddenly it will start misfiring and will continue to misfire for varying periods of time. Sometimes less than a minute but sometimes for extended periods of time. As an example, yesterday the car was running fine when we pulled into the pharmacy drive-thru and continued to idle fine for over 10 minutes but then suddenly started misfiring and continued to do so for the next 10-15 minutes both while sitting in the drive-thru as well as while driving home. It happens both when the engine is cold and when hot. When it misfires, I notice that the tach drops by several hundred to over a thousand RPM. I also have noticed a gassy smell and the transmission does not shift normally although that could be related to the RPM change. I also noticed the other day when it was warmer outside that the car started to get warm like the cooling fans were not working. I did verify that the cooling fans work when the AC is on but haven't verified the temperature switch for the fans.

I jumpered the EEC today with the car near operating temperature and got the following codes:

KOEO
172
173
181
216

KOER
213
538
536
521
632

A search of this forum lead to several potential issues but I thought I'd ask for input before I start changing out parts. I'll admit up front that I don't have much experience with troubleshooting automotive electronic controls (my expertice is more in the area of mechanical diesels) so any suggestions or guidance would be welcome.

 

[luigisho]

213 really stands out. Make sure that is correct. points to potentially failing DIS module or maybe even a computer problem. Check the sides of the DIS for cracks or poor contact at the wiring plugs and make sure the screws are both mounted as they provide ground for the module. Do you have a lot of engine movement under the hood like a bad mount? Shiny rub spot on the front of the intake from contact with the hood?

 

[12valve@heart]

I'll recheck the codes after I drive it tomorrow but I'm sure that 213 was showing today since I checked the numbers twice. The DIS is securely attached and doesn't show any cracks. I put dielectric grease on the connections tonight so we'll see if that makes any difference.

Interesting that you mentioned motor movement because the front motor mount is collapsed and is on my list to replace. There is one small area on the intake that shows hood pad contact.

Thanks for the input. A DIS at the local O'Reilly's looks like about $157. Is one from the auto parts as good as OEM or do I need to visit the Ford dealer?

 

[luigisho]

I would investigate further before I start throwing parts at it. I haven't heard of any complaints of aftermarket DIS units. It could be a wiring short somewhere. Intermittent symptoms sound like a bad sensor or electronic component but you can spend a lot of money throwing parts at stuff.

 

[rubydist]

The 216 says you have a coil failure, which will certainly cause a misfire. Unfortunately, about 50% of the time this code is actually due to a failing DIS rather than coil. Given that it comes and goes apparently at random, and that it occurs both hot and cold, I would replace the DIS before the coil. I would look for a junkyard part first, since it will be more like $20 than $150, so worth a shot, but make sure you put heat sink compound under it when you install it so it does not fail right away.

Then I would reset the codes and drive for a while to see what pops up. The fact that you have the pcm complaining about both rich and lean on the right bank tells me you have old codes in there, you can get mislead by old codes...

 

[luigisho]

Totally agree with above. I try to have some used parts on the shelf for stuff like this.

 

[12valve@heart]

Thanks for the input.

I pulled the positive battery cable yesterday and let the car sit for about 45 minutes. Had to reset the clock and radio when I hooked it back up. Hopefully that cleared the old codes.

Drove the car today and after I got home, I got the following codes:

KOEO
111
111
216
216

KOER
213
538
536
632

Would that still support the DIS being a prime suspect?

I also noticed that when I tried to rev it up after I got home and it was misfiring, it reved like it was bouncing off a rev limiter but the tach was stopping at about 2500RPM.

Thanks again for all the input and suggestions. I'm going to start looking for a used DIS as a starting point.

 

[super-sho]

Check the plug wires. Carbon tracking at or near the boots will cause intermittent misfiring - most noticeable when the engine is low RPM under load. At times, the engine will run fine and then just start misfiring. I took my car to the FORD experts and they said it needed a new computer which was furthest from the real fix. New plug wires - and make sure you clean all the powder off the outside of wires before you install.

 

[luigisho]

What did your 60k include? A used DIS isn't a bad idea. See if you can find a local-ish yard with a GenI or II. The DIS was used in some Tbirds too I think supercoupes

I see some on ebay for about $30

 

[rubydist]

yup, I would find a used DIS and replace that first of all.

you got rid of the o2 sensor codes by resetting - now you need to check again in a week to see if any of them have returned (it takes a little while for them to reappear).

btw, when you are running the key on, engine running test, you need to goose the throttle, tap the brake pedal, and turn the steering wheel back and forth at the right point of the test - doing that correctly will most likely get rid of the 536 and 538 codes. if not, you need to find out why the brake lights don't work!

 

[12valve@heart]

Yep, put a used DIS in it and have driven it for most of a week without it misfiring. Thanks for the suggestion.

 

[rubydist]

good news.

now check for codes to see if the o2 sensor codes are coming back or not.