jtrask

Is the timing on an 87 4.0 adjustable? I'm getting conflicting statements from the mechanics. One says the distributor goes in only one way and that the timing is not adjustable. The other says the timing needs to be adjusted using a timing light.

Which one is correct?

cruiser54

The timing is adjusted by the ECU. You cannot adjust it. You can observe it though with a timing light.

mike albo

the 4.0 timing is not adjustable,the distributer goes in one way

ol'DixieJeep

this is interesting... how does the ecu adjust timing? if the timing is off, as in the ecu is not adjusting correctly, how do you fix it? doing a soft reset of the ecu?

cruiser54

The ECU adjusts timing using the CPS signal. Never seen an ECU problem with ignition timing.

What in the world are you doing and why?

highmileage

sounds like it could be a dirty or old CPS

cruiser54

The distributor housing can only be clamped down in one position. It needs to be "indexed" so that the rotor is pointing just past the #1 terminal on the cap when the engine is on #1 cylinder TDC..

Cherockee

This is the first time I've ever heard to set the rotor "past" the #1 cylinder... where did you get that information?

cruiser54

From being a service manager and shop foreman at a Jeep dealership from 1980 til 1992.

Remember: The distributor innards on a Renix only control the sequential injector firing. That's what the indexing is all about.

Cherockee

And just so I'm understanding this correctly, would this still apply to non-renix 4.0L up until 99?

cruiser54

Uh, no. OP was inquiring about Renix and differing stories he got from mechanics.

I think there's someting in the later dizzies that requires doing something with a toothpick?

Cherockee

Okay, thanks. Just wanted to be sure as I have not worked with the older motors. The later dizzys have a guide pin to locate the cam positioning sensor when installing the dizzy into the block.