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Weak coil?

mattbred

NAXJA Forum User
Location
Canada
My '89 Cherokee 4.0L has lacked low end power since I bought it, but it seems to have gotten worse over the past few months.

It has stock 3.07 gears, an AX15, and worn out 235's.

-If you drop the clutch at around 3000 RPM's, it'll simply bog down instead of spinning the tires unless you are on dirt/loose surface.
-If you rev it while in neutral, it'll hesitate before doing it
-Never ever chirps the tires
-When it's cold, it'll stall at the first stop sign every time
-After I let the clutch out and start to really give it some gas, it'll keep the same rpm's for a second and then take off, almost as if it's bogging down but not quite.
-It seems to have OK torque, not a monster by any means like the claims I've heard, but when it reaches 3500 RPM's it seems to get a bunch of more torque, like it just got a bunch of boost
-Runs better when it's hot
-Stumbles at idle. Will occasionally stumble to 500 RPM's and sputter. Holding at 2000 RPM's it sometimes missfires as well.

I've done a full tuneup, replaced the O2 sensor, TPS, checked my MAP sensor and temp sensors. Fuel pressure is good. Engine was rebuilt 70,000 km's ago by PO. Checked for vacuum leaks yet havn't found any. Could these be signs of a worn coil?

On a side note, my Haynes manual says that the voltage going into the bottom of the distributor should be 5 volts, but when I checked mine last it was 7 volts.

Edit: Also where does the signal for the tachometer come from? I notice that sometimes the tach will hang and then jump up a couple hundred RPM's, even though the engine was revving steadily. If it comes from the coil, could it be related?
 
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Ok for the 2.5 that might be a bit more normal, but I know that I had the same set up only rolling 33's, yes with 3.07's and I could still chirp the tires in the least. It sounds to me like it is a CPS issue. Check out this site:
http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm
Lots of great info on his site, this is directly to the sensors. However if you were to look at your tach signal you could do so on pin 1 of D1, the diagnostic hook up in the engine bay. I am pretty sure that the issue is going to be with the CPS (crank Posistion Sensor). Sorry it is kinda a PIA to change out, oh when you do go that route make sure that you get the one for 87-90 not the newer one. They are different and not interchangeable from what I recall. When I did the CPS on my 87 I found it was a little easier for me to reach it with the front driveline dropped down. Good luck and thanks for all the info. You may also want to read up on the renix files here on the board. Great info and lots of trouble shooting on there.
 
Oh I've read all those tech pages and the RenX files thread.. Still dunno what my problem is. Don't CPS's just fail outright? It runs really good except for the low power, which doesn't seem like a CPS problem.
 
Hm, I can't chirp my 32's in my 95! 4.0, AW4, 203,000 miles.

Do you think it could be the TPS as well?

I had 30's before and I couldn't chirp them either, couldn't even do a burnout either unless I was on loose gravel!! Seem to be lacking some power myself as well. Sometimes when climbing up a steep-ish hill, even in 4lo, sometimes I'll have the pedal all of the way down and it will just load up and spin nothing at all.

Everything else is quite new. Plugs, coil, cap, wires, o2 sensor, etc. Cat is a year old as well.
 
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