timing mark jumps erratically

[isnms]

When I check my timing, with the diag block jumpered, the mark jumps around 10° erratically. It has, about, a 6° swing window, maybe 5°, it's not marked in single increments. When I remove the jumper, it advances to ~12° but with the same amount of swing, jumping, fluctuating, bouncing,...

In other words it is not steady on 10°. Is this a problem? If so, what could cause it? If not, I'll quit worrying.

 

[CRE]

Could be a worn timing belt or the idler (belt tensioner) needs replacing. Are you sure you're getting a good connection when you jumper the diag box?

 

[jetjock]

Could be your TPS. The IDL contact in the TPS must be closed to set base timing. Also, the ISC system is inactive with IDL open.

Check to see if you have a code 51. You shouldn't with the throttle closed and should with the throttle cracked. Check this in diag mode, engine off. Either that or break out your meter and check for continuity across the IDL contact with a closed throttle.

 

[isnms]

I'm sure jumper had good contact. I'll look into the idler.

No codes. I've done the tsrm adjustments on the TPS and it seems ok.

Would CPS affect this? I need to rewire the connector anyway. I sometimes get a code 12.

 

[jetjock]

It sure could because ignition timing (and a lot more) is predicated on CPS generated signals. The CPS is the heartbeat of your EFI system. You need to fix that anyway as it could strand you. Code 12 signifies a loss of NE (rpm) or G (crank angle) input. The ecu can't do squat without either one.

 

[isnms]

Yeah, a couple times it wouldn't start. Wiggle that connector and it fires right up.
I'll fix that and see if the timing mark settles down.

 

[MDCmotorsports]

Could also be a broken lower pulley. They are steel/rubber/steel. The rubber inside tends to break down.

 

[isnms]

How about a crappy timing light :icon_idea

I did do some work on the cps connector wires. Then went to check the timing. The light wouldn't work. I saw it flicker a couple of times, then nothing. I ran up to AutoZone to pick up a new one. My timing mark is not jumping around like it was.

 

[billspreston01]

my timing does that too but everything is AOK with my electronics, no codes, idles just fine...etc etc etc. Mine only bounces like 3degrees though (haven't checked it in a while)