Camshaft timing and ping

[likestogofast]

I installed a new cam in my stroker and I am having trouble with off idle through mid range ping that was not there before. The cam profile is the same before and after. When I degreed the new cam it was a degree or so retarded so I installed a 2 degree offset key to advance it. I don't know with 100% certainty that the first cam was installed at the same intake centerline because I didn't write it down the first time.

I have checked:

Distributor indexing
Fuel pressure (50 psi at wot)
TPS voltage (0.6 to 3.7V)
MAP voltage (1.3V at idle, no MAP adjuster)
Initial ignition timing (12 deg)

This is in a CJ with OBD1 PCM, no MAP adjuster, Hesco aluminum head, Hesco fuel pump, Ford/Bosch blue top injectors, and 99 intake. The ping gets worse in closed loop, but it's basically undriveable either way.

Engine specs are on the attached screenshot from the compression calculator. Could a couple degrees of cam timing alone cause this? If not, what else should I check?

[RenoF250]

So this is a new cam with the same grind as the previous? The compression sheet says 8deg advanced is that correct? Remember when you advance the cam you advance the distributor, did you adjust accordingly? What octane fuel are you running? I would not expect a ping with an 8.2 DCR. I take it those are custom pistons?

[6TIME]

What cam were you using before and what cam are you using currently? Have you checked your cranking compression #'s?... That may provide some insight.

[likestogofast]

Same cam as before, see attached.

91 octane. I have tried upping the octane to about 93 with race gas, didn't fix it.

Reno - are you saying that the distributor needs to be more advanced than the normal setting? I thought changing that would not change timing?

[SilverXJ]

Are you sure those numbers are correct you entered in the calc? Specifically the piston dish(35cc) and combustion chamber(47cc)? What cam is this? 8* advanced?

[likestogofast]

Oops, forgot to attach the pic of the cam card. I'll do that when I get home. The cam is a custom grind Comp 250/208, 113 LSA on a 108 ICA. I inadvertently attached the pic of the compression calculator with the "high" advance that I was messing around with to see what it did to the DCR. If you plug in 5 degrees advanced the DCR is 7.99.

[RenoF250]

Same cam as before, see attached.

91 octane. I have tried upping the octane to about 93 with race gas, didn't fix it.

Reno - are you saying that the distributor needs to be more advanced than the normal setting? I thought changing that would not change timing?

Since the distributor is driven from the cam it will advance with it so if you advanced the cam 5 degrees the distributor is advanced 5 as well. I am not clear how the timing works on these, I know on my 4.2 I can move the distributor and the timing does not change but I have read many on hear cutting tabs on the distributor so they can turn it, must have some effect. Hopefully someone with more knowledge on it will pipe in.

[likestogofast]

Cam specs attached.

The pistons are custom dished CP.

The head is the Hesco aluminum, with some chamber work.

[RenoF250]

Cam specs attached.

The pistons are custom dished CP.

The head is the Hesco aluminum, with some chamber work.

If you are pinging at that compression with an AL head it pretty much has to be ignition timing. I would look into that closely.

[6TIME]

Can you get some cranking compression #'s? That cam looks very similar to the 232-4. You said your spark timing was 12* was that at idle?

[likestogofast]

I'll check that when I get some more time, probably not until next week. Correct, 12 at idle.

Thanks for the replies.

[6TIME]

If you have a light with advance adjustment or timing tape etc.. check the spark advance @2500-3000. it should be in the mid-high 30's

[SilverXJ]

Moving the distributor effects the injector timing more than anything. Which could cause your problem. I don't see anything in your combo that would cause too much compression an cause pining. I would suspect something fuel or ignition related.

[6TIME]

Moving the distributor effects the injector timing more than anything. Which could cause your problem. I don't see anything in your combo that would cause too much compression an cause pining. I would suspect something fuel or ignition related.

Agreed. I've rotated the dizzy with a light on the damper and it doesn't change much until you get it waay off. If the dizzy is a tooth off it definitely dorks up the spark timing tho.

[likestogofast]

I have set the distributor at "zero" at a few degrees (maybe 1/8") advanced and a few degrees retarded and it did not change/correct the problem. Centering the distributor on the advance/retard rotation that results in a stumble puts it pretty close to the "zero" setting. Also, had the distributor clocked at zero with the original cam, no ping. So I have stopped looking at the distributor for now anyway. I originally thought for sure that was the problem, but I think I have eliminated the distributor clocking.

I will get to the compression test next week and see what that shows. I may also hook up each injector to a jumper and give them a run to see if there is anything funny going on there. No codes to indicate an injector problem, but I don't trust the OBD1 to tell me much more than complete failure of a particular component.