New CPS sensor, Now timing is off.

[SkipshotMJ]

Hey guys! Its been a while since i posted last. The comanche has been running pretty damn good lately. Well finally my truck died on me again. I was driving around turned off the main road, hit a bump, and the comanche died. I tried to start it, but nothing. I knew it was the CPS sensor so i checked and it was. The wires going from the CPS sensor to the wiring harness had been too close to the header for to long and fried. I had a replacement and installed it, but now the comanche is running as if the timing is off. I had been using a high altitude CPS sensor (supposedly advances the timing) for the past year or so and it was running great. The replacement sensor was stock. I checked the timing by finding TDC and looking at the distributor (rotor and cap placement) and it was dead on. I'm about to go order a new High Altitude CPS sensor, but does anyone have any ideas? I have an '87 Jeep Comanche 4.0L I6 and AX-15 Tranny.

[Geonovast]

All the timing is controlled by the computer, so really the only thing mechanical that can screw up your timing is a broken chain, and if that happens, timing is the least of your concerns.

 

I'm betting it's either 1. That you're in an area that needs the high alt CPS, or there's something wrong with the replacement you got (not uncommon).

[Eagle]

I don't think you need a high-altitude CPS in Monteray, CA. But, irrespective, the CPS doesn't control the ignition timing. It sends a signal to the ECU which, in turn, compares the crankshaft position to several other inputs to determine when to fire the plug. Either CPS gives you as much advance as the engine can handle short of getting ping. When the knock sensor detects ping, it retards the timing enough to stop it before you grenade a piston.

 

The high-altitude CPS is offset a couple of degrees so that UNDER LIGHT LOADS you get a couple of degrees more advance, and maybe better gas mileage if you're near sea level. Once you mash the throttle under load, the knock sensor is what's going to limit your timing advance, so I don't think replacing the CPS is likely to fix whatever problem you are experiencing.

[Jeep Driver]

Will the high alt sensor help a 2.5 gain any low end power?

[airspeed]

I have a high altitude 2.5 and when I put a timing light on it I see about 14 degrees BTDC. At sea level that would probably give you pre-ignition, knock.

[Eagle]

Will the high alt sensor help a 2.5 gain any low end power?

No.

[Eagle]

I have a high altitude 2.5 and when I put a timing light on it I see about 14 degrees BTDC. At sea level that would probably give you pre-ignition, knock.

Which is why there's a knock sensor ...

[HOrnbrod]

I have a high altitude 2.5 and when I put a timing light on it I see about 14 degrees BTDC. At sea level that would probably give you pre-ignition, knock.

 

12*-14* BTDC is what you normally see with w. a timing light no matter what CPS you have.

[airspeed]

My 88 2.5 does not have a knock sensor.

 

Why would there be a high altitude CPS if the timing is the same?

[HOrnbrod]

Why would there be a high altitude CPS if the timing is the same?

 

Read Eagles reply above.

[airspeed]

There is NO knock sensor on the 88 engine and fuel controls for a 2.5L.