[austin9393]

hi i have a 93 mustang 2.3 liter and the tach doesn't read correctly sometimes it reads right then it starts bouncing up and down very eratic i have replaced both coil packs plugs and wires and the ignition control module thanks for looking any suggestions would help

[lugthug713]

Do you an after market tach tapped in to your sach. B/c I do and mine bounches all over, because of that

[austin9393]

no but i thought about putting one on and maybe that would fix it thanks for looking

[Eaglestang]

Try Replacing Engine Control Module, Or Replace The Module Which It Is Sitting On The Intake Manifold.

[saaws2]

get a new DIS box its on the upper intake thats what mine was doing then it just started to run really really bad

[austin9393]

ya i already replaced that

[austin9393]

i am also getting a 538 code which means rpm change during dynamic test

[sgtb]

I'm guessing that you have seen these two threads:

http://www.allfordmustangs.com/forum...ing-223-a.html

http://www.allfordmustangs.com/forum...-223-loss.html

Several others and I also had this problem and by replacing the DIS module the tach cleared up.

If you have replaced the DIS did you get the new one checked to make sure that it wasn't bad off the shelf?

Also, maybe you don't have it mounted on the manifold with some of the thermal paste that helps get a good connection and keeps it cool (someone said that it need a grounding contact - I'm not sure about that but either way it will help keep it cooler).

I can't remember for sure, but when my DIS was bad I think that I had a similar problem trying to run some of the diagnostic test because the rpms would bounce around. But I don't really recall if I got a trouble code for that or not. I assume that you also previously got the 223 codes that the rest of us got and that went away when you replaced the DIS...

Did you replace the DIS and the coil packs with brand-new ones or second-hand? I think you can get the coil packs tested at some auto parts stores also (autozone maybe). Like I mentoned in my other posts I had to get them to test my DIS about 5-6 times in a row before it failed. But that is what it did in the car also, the tach and check eng light would come on and go off intermintenly.


On another note, since you mention the tach and you didn't say that the car was running bad at the same time... (in my case the tach was just reflecting how the engine was actually running - crappy) a long time ago when my car was still under the mfg warranty my tach started acting up (bouncing around etc) and the dealer replaced it with one out of a 5.0. Then it read steady but only at half of what it should have. I had to take it back and they put in the right part... All this to say, are you sure that it isn't just the tach?

If you've already read the two threads at the top and none of the rest of this helps then I'm at a loss.

I'd start blaming the tach itself - or maybe a broken wire somewhere?
Maybe some auto store or shop can test the tach itself.

MB

[austin9393]

ya i was getting both of those codes and replaced both coil packs and it went away then sometimes when im sitting still at the light the car runs rough and i get a 538 code which means cylinder identification problems and throttle movement during dynamic test or something and just the other day i put some seafoam in it and it seemed to help it out then it came back not as bad and i took the old control module back and got a new one under warranty the second one

[sgtb]

Originally Posted by austin9393

ya i was getting both of those codes and replaced both coil packs and it went away then sometimes when im sitting still at the light the car runs rough and i get a 538 code which means cylinder identification problems and throttle movement during dynamic test or something and just the other day i put some seafoam in it and it seemed to help it out then it came back not as bad and i took the old control module back and got a new one under warranty the second one

"the second one" what?
Maybe this is common knowledge to everyone but me, but what is "seafoam" in the way that you are using it? An engine additive or something?

Are you sure that when you changed the coil packs you got all the wires back in the right places? I don't meant to insult your mechanical skills, but having nearly messed that up a time or two myself I know it's possible even when you're careful...

has the timing belt been changed? did you double check the engine default timing sensors? The mechanical timing is pretty easy, but maybe if the bottom belt pully (if I remember correctly from when I changed the timing belt it's the crank pully) that has the flanges on the back side that have something to do with the engine spark timing or delay as they pass by a couple of sensors. (don't quote me on this it's been several years and I don't look at it every day. I could look it up again if it is something that you can't find out from my rough description.) Anyway, If what I remember is right, maybe the sensor is out of place or a wire is shorting or something.


when I just did a quick google for Ford engine code 538 i found it to indicate "Insufficient RPM change during KOER Dynamic Response Test." (from Diagnostic Trouble Codes which also has a diagram that looks like it is how to get the codes without a reader box, just by using the built in test socket and a jumper - but since I bought the cheap little beeper tester I haven't done it that way in many years either...)

if the 538 is "insufficient RPM..." and not "cyl id problems..." then I may have gotten that code it sounds vaguely familiar. But after I got the DIS all good and mounted I haven't had any trouble codes at all through any of the test that I did.

here is a link to the trouble code information from allfordmustangs.com
http://www.allfordmustangs.com/Detailed/445.shtml

anyway -- maybe this will help...

MB