Timing all over the place ?

[F1boats]

I have a 1997 Jeep Cherokee With a stroker motor. Will not bore you with details of the motor. My problem is timing its all over the place I am reading the timing with a Innovate Motorsports LM2 Data logger what a great tool ! My distributor is a new rebuilt so the cam sensor is good. Timing is all over the place sometimes for example 3500 may be as low as 20 to 27 DGs at 4000 20 DGs if you can get it to go past 4700 it can jump to 44 DGs its just totally going crazy. Of course when the timing drops it goes very rich also logging air fuel ratio. Question is it a crank sensor or brain box or who knows driving me crazy ! Any help I will grateful for. Peace <><

[superj]

timing chain?

no idea since mine is carb'd but the chain or the weights/springs on the distributor being loose/messed up would cause those issues for me

[F1boats]

I am even more confused now that I drove on the highway with the jeep when I step on the gas the timing goes down and then when i let up on the gas it goes up WTF ?

[SilverXJ]

How is the lm-2 reading timing?

[F1boats]

Through the OBD2 port

[Cheromaniac]

timing chain?

no idea since mine is carb'd but the chain or the weights/springs on the distributor being loose/messed up would cause those issues for me

The 4.0 distributor doesn't have any weights/springs to get messed up so my money's on the timing chain being overstretched. Pull the distributor cap, use a ratchet wrench to turn the engine by hand, and observe the rotor. If it takes several degrees of crank rotation before the rotor even moves, you'll know the chain has too much slack.

[F1boats]

The distributor just tells the injectors to fire. The timing is a combo of crank sensor MAP sensor and ECU as far as I know. Any info is helpful thanks

[Cheromaniac]

The distributor just tells the injectors to fire. The timing is a combo of crank sensor MAP sensor and ECU as far as I know. Any info is helpful thanks

The dizzy does a bit more than just tell the injectors when to fire. It also distributes the spark to each cylinder and the cam position sensor synchronizes the injector firing with the spark. If there's too much slop in the timing chain the spark timing and injector firing are going to be all over the place.

[ossme]

Please keep us posted as I'm having the same issue..

[F1boats]

How are you watching you timing ?

[Coffee Commando]

Doesn't the ECU control the timing based off of the crank and cam sensors? I've also heard that the MAP sensor readings are taken into account.

Don't forget the TPS reading at 70% sends the ECU into to open loop, so if you're holding the throttle high enough to get to 4000 RPM's I would think the timing is going to be adjusted.

Is your engine running like crap or is it just something you noticed with the LM-2? I would think that the timing wouldn't be static since the ECU is supposed to control it for maximum performance.

It may be that one of your sensors is bad and is causing this if the timing isn't supposed to jump around that much. But if that was the case you would have an OBD code. Do you have any OBD codes and a CEL?

[gradon]

I don't know about your lm-2 on your 97, but my lm-2 on my 96 can only handle 4 high-priority obd2 readings live before it bogs and then all the data is useless and varies all over the place. Maybe the can-bus Jeeps provide faster info or maybe it's the lm-2 limitation. Try just an RPM, TPS, and Timing datalog.

[SilverXJ]

His 97 isn't can bus. It still has a Chrysler bus (SCI?) that is used for modules to talk to each other, but you don't get access to it with an OBDII scan too. But, you are right in the bog issue.

[F1boats]

I have only tried 4 on the lm-2, timing, air/fuel,map and rpm. I think these are the most important.Please correct if I am wrong. Thanks