Tach problem

Shawneebear93

Shawneebear93

Dirt-Old 20+Year Member
May 4, 2004
518
17
49
Salisbury Twp, Allentown, PA
#1
Tach is reading low. Idle is reading ~600, where is it's usually 800. When I'm on the throttle and it's reading ~1,500 it really should be closer to 2,500. When it would be normally around 3,000 it kicks up for a second to 3,000 and then drops right back down. I got a code scanner from my girlfriend's Dad to check it out, but it's only for 1996+ vehicles. I called AutoZone and the guy told me he couldn't do my car -
Me: "Do you have code scanners I could use there?"
AZ: "Yea we do it right here for you in the parking lot. Is it OBDII?"
Me: "I really don't know, I've never used one. It's a '93 Mustang."
AZ: "Oh a '93 Ford, we can't do that. Sorry."
Me: "****. Thanks anyways."
AZ: Laughs, "Have a nice day."
I read through some old posts saying it sounded like the ICM, sound right?
 

  • Sponsors (?)


#3
ICM is what causes a code 223/224 and the tach to be off. There's a complicated way to check it without a scanner, but it takes some time. The ICM is also what controls the tach, so if it has never been changed, chances are since every single DP 2.3 has needed it, you might too lol. About $120 new, and get a new one. Don't go with a junk yard one because it will have the same problem most likely.

*oh and yeah, check coil packs. Mine was cracked and shorted the ICM and caused driving problems.
 
#4
I just got back from my mechanic and he pulled the codes. I am an idiot and didn't write down what codes came up (the mechanic did). But 4 or 5 came up. One was for the Mass Air Filter, one said all 4 cylinders had something wrong with the coil pack (which you all have said) and there was something with the Dual Plug Ignition (which the mechanic said he never saw before) and and EGR code came up (which he said is a problem on all Fords). He reset it and said if they were a problem they'd be back in a few days and I should give him a call.
 
#5
It's the ignition module, no doubt...don't bother trying to figure anything else out.

Oh, and the tach is reading exactly half of the "normal" rpm because only 4 of the 8 spark plugs are getting spark...which is also why it's throwing a Coil code even though they are fine.
 
#7
stinger is right dont bother with the icm ,ignition modules are terrible on our cars and dont be suprised if autozone or another parts house gives you a bad one took 3 times for me to get a good 1
 
#8
It's located on the front of the intake manifold. grey box with wires coming out of the top and bottom.

To replace it you just unbolt it, put some new grease on the back of the module and bolt it on.
 
#9
attachment.php


This is where it is on the lower intake. I had mine go bad on my 92 too. Its a easy fix just be sure to put the grease on there like Stinger said.

Dan
 
#10
listen , it might be your ICM , but Before you buy anything , they can test your ICM at the store. Take it off AND HAVE IT TESTED. Everyone was telling me too , " its your ICM , just buy a new one ". Well I took it off and had it tested , and it was fine. I'm telling you , a coilpack is alot cheaper to replace than a ICM. And yes they can test coil packs too.Just take them off ( ICM , Coil packs ) and have them tested before you buy anything.:nono:
 
#12
From my experience with my 223 and 224 codes. The parts stores tested my coil packs and my ICM and found both to be just fine. Kinda funny that the car runs great with the new coil packs and ICM. I have had bad alternators that have tested ok, but are bad too. On my deal, I still don't know if the ICM was actually bad for sure because it always tested good. I bought my stuff from O'Reilly's, Got lifetime warranty on Berg Warner parts, cost $337 for all 3 parts including dielectric grease. Spend a little on her, she is worth it.
 
#13
jgt58 said:
BTW , if it was the ICM , the car would not run right at all and Die. If you have a coil bad , only half of the plugs are getting spark , hence the drop in RPM. I think this is a more sensible explanation.:D
Click to expand...


While I'm not doubting one bit you had the trouble you had, I will say(from first hand personal experience) that a bad ICM can and will run the car just fine, the only symptoms will be a check engine light, and an erratic tach. You're not actually dropping RPM's they're being misreported.
 
#14
When I was having problems like that and soon after the car started missing like crazy then firing on cylenders 2 and 3 only. I ended up having to change the module and one of the coil packs that was bad. In my expiriance unless the coil packs are badly cracked and look like there firing through the crack, or are melted somewere and look like its firing to somwere other than the plug wires than its probaly not bad. Otherwise just change the icm and go from there sounds like youll need one of thouse reguardless. Good luck with your car, Nick
 
#17
jgt58 said:
listen , it might be your ICM , but Before you buy anything , they can test your ICM at the store. Take it off AND HAVE IT TESTED. Everyone was telling me too , " its your ICM , just buy a new one ". Well I took it off and had it tested , and it was fine. I'm telling you , a coilpack is alot cheaper to replace than a ICM. And yes they can test coil packs too.Just take them off ( ICM , Coil packs ) and have them tested before you buy anything.:nono:

BTW , if it was the ICM , the car would not run right at all and Die. If you have a coil bad , only half of the plugs are getting spark , hence the drop in RPM. I think this is a more sensible explanation.
Click to expand...

Just so you know, the ICM's (or "ignition module") only fail after heating up. When tested, they never get hot so they only show "bad" if there is a no-start/no-run condition with the vehicle it came off of. Even then they sometimes test "good" but the car starts once they are replaced.

Also, so you know. The tach signal comes from the ICM, not from the coil packs. If the tach is reading faulty, the ICM is bad, bottom line. No if/and or buts about it.

Also, if you knew how the dual plug ignition system worked, you would understand that the engine can run perfectly fine on 4 spark plugs (just like every other 4 cylinder engine). If you don't believe me, unplug one of your coil packs and start your car/drive it around...you won't notice a difference except the CE light will be on. That blows your whole "if it was the ICM , the car would not run right at all and Die" theory out of the water.

(Just a little background on this problem)
I went through this jumpy tach problem when I first bought my 91 Mustang years ago (before this problem became "common knowledge" on this forum). I had it all tested (coils, ICM, etc.) and everything tested great. I still knew something was wrong though because when the tach would read half of actual rpm, I would get no fire to half of the spark plugs. Immediately I thought it was a coil pack but that's easy to check. I simply swapped the front coil to the back and back coil to the front and retested the spark. If one of the coils was bad, the no spark on 4 plugs problem should have moved with the coil and now been not firing on the other side of the head. It didn't happen (coils eliminated as a problem). I Then went through the whole ignition diagnostics procedure only to find no problems. I decided to not worry about it because the car still ran fine. 5-6 months later I shut it off in front of the house and it wouldn't start when I came back out a few minutes later. Checked it out and had no spark. Decided to buy an ICM because I knew it was the source for the tach signal and sure enough...started right up and never had any problems with the tach, check engine light, or no spark condition ever again.

BTW, can someone sticky this thread or put it in the FAQ or something so it's not asked every couple weeks (or we can at least point them to it when they do ask).
 
  • Like
Reactions: 1 user
#18
16vstang said:
Ignition control module and yes you do but its a different style one. its located on the dizzy. Should have just one plugin though on the left side I bleive.
Click to expand...

Also known as a TFI (Thick Film Ignition) module. Oh, and it does have just one plug but it's on the right side (or pointing towards the rear of the car), however you want to say it.
 
You must log in or register to reply here.

Similar threads

J
2004 mustang gt 4r75 trans
Replies
1
Views
357
SN95 4.6L Mustang Tech
Yel2002GTAuto
Y
L
Cannot get P1000 code to turn *on*
Replies
1
Views
190
2005 - 2009 Specific Tech
Bullitt347
Bullitt347
93CalypsoConvert
Fox 4 Cylinder to V8 Tach
Replies
45
Views
6K
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
93CalypsoConvert
93CalypsoConvert
A
Help with engine issues/emissions
Replies
13
Views
765
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
Mcmahst
M
B
Runs really rough - Code 212
Replies
13
Views
1K
1994 - 1995 Specific Tech
BrightVa
B
Top Bottom
Back
New
Hot
Menu