90 sc driving me NUTTS runs great then only on 4 cyl.

cindis35th

Registered User
I can't complain a whole lot, my car has given me over 200,000 miles of great driving pleasure with the original motor, supercharger and manual transmission. Recently though I am having a problem that we can't find a fix for, I will be driving along fine then the two back cylinders cut out, the rpm's drop and it runs rough with little to no power. We ran the code scanner and it came up with an egr malfunction. So we went to replace the egr valve, during the removal of the egr valve the egr tube became damaged. Well Ford no longer makes the egr tube and I haven't been able to locate one. So just to get the car running we installed the valve, plugged the vac lines and now it just sucks fresh air, we plugged the were the tube goes into the exhaust. I can drive for a few days with no problems then other days it runs on 4 cyl no matter what I do.
We have put in a new crank sensor, swapped the DIS and coil pack. If we run the code scanner when it running bad it comes up as a 4 cyl car. Any ideas as to what it could be???? I don't know if these issues could be related but I'm also having issues with the temp gauge, it flip flops all over.
Any ideas would be greatly appreciated, also if any one has a schematic of the injectors and gauges
 
get a new DIS module from Auto Zone, get some Arctic Silver heat sink compound from a computer place (best buy I think has it), put it on the bottom of the dis, mount dis, start car, problem should be solved.

Temp switch is the reason your guage is screwy (hopefully). It's a 4 dollar part that threads into the water neck by the blower. Has a little connector, check to make sure the connection is good.
 
As for the EGR, there is a block off plate you can mount to the back of the inlet plenum to bypass the valve. Then you need to plug up the pipe or remove it from the manifold and get it plugged or welded shut. The Check Engine light will stay on, but if you get a tune they can turn the EGR function off in the computer and no more light. The car will run fine without it if you bypass it the right way.

Swapping a DIS isn't always good, I swapped one it was bad too. Bought a new one, car runs great.
 
Actually, the temp sensor is an actual variable resistance sensor, not just a switch like the oil pressure sensor.
 
Thanks for the posts!

I already replaced the temp sensor with a new one and I know that my car is not heating up so that is not critical for me. It the intermittent running on 6 cyl then dropping to 4 cyl and when we check the coil pack it's always the two back cyl that have no spark. If I drive on the freeway it will last longer than if I am driving in the mountains. Will the DIS cut in and out like that?
 
It the intermittent running on 6 cyl then dropping to 4 cyl and when we check the coil pack it's always the two back cyl that have no spark. If I drive on the freeway it will last longer than if I am driving in the mountains. Will the DIS cut in and out like that?
Yes. Get a new(er) one. :cool: Razor thin layer of heat sink grease on the bottom.. in this case, more is not better.
 
Actually, the temp sensor is an actual variable resistance sensor, not just a switch like the oil pressure sensor.
The temp guage sensor has a linear resistance that varies with temp.. the ECT sensor (the one monitored by the EEC) is a thermistor which has a non-linear resistance change with temp.
 
The one that runs the gauge is listed as a temperature switch in the parts catalog. I can't think of the company that makes it off the top of my head, but I got one for about $4.00 at Auto Zone and it was looked up as a temperature switch. The coolant temp sensor is the one that talks to the computer.

Yes the DIS will just cut spark out of two cylinders. I got a few minutes down the road and the car starts to run very bad, no power, etc... A few minutes later it's back to normal. Did this for a few weeks till I got a new DIS. Changed it, drove it through 5 states non stop, and not one hiccup out of the ignition.
 
The one that runs the gauge is listed as a temperature switch in the parts catalog. I can't think of the company that makes it off the top of my head, but I got one for about $4.00 at Auto Zone and it was looked up as a temperature switch. The coolant temp sensor is the one that talks to the computer.
Yup. It makes it tricky to find one. And with these cars being so sensitive to overheating, I wouldn't recommend ever drving without a working temperature guage.
 
THANKS GUYS FOR ALL THE INFO!

As far as the temp guage, I'll go and get a new switch, I have already replaced the sensor. I have been lucky so far, my car has never overheated. I had heard that is a problem with most SC's but I haven't had that problem. Just to be safe, since I have had my car so long and all the miles I've put on it I put in a new radiator and water pump last year. I had only mentioned the guage because it started going crazy about the same time as intermittent 4 cyl - 6 cyl problem. Which for now I stuck my old DIS unit back on until I can find a new one. The only problem with the old one seemed to be intermittent tach function, but it didn't effect the way it runs and I can live with that.

Again, thanks a lot for the posts ;) I find so much info on this site, it's great to find a site that is still up and running with so much info.

Cindi
 
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