I had recently been experiencing backfiring and poor performance, I pulled the distributor since I could not obtain steady timing and found my distributor gear is extremely worn thin on one side. Did not see any damage on cam gear. I may have used wrong gear considering I have a Hi-volume oil pump and the roller cam.

I have since installed a new bronze gear even though I know the cam gear is a cast shrink gear to recheck the timing. The base timing cannot be set accurately, the timing wonders once under about 15 degrees BTDC. If I lock it down at about 10 BTDC and reconnect the ECM bypass the timing wildly oscillates at about 10 ATDC after the engine is warm. On a cold start, the ECM seems to be OK holding the timing at about 15~18 BTDC but slowly deteriorates as the engine warms as mentioned above.

BTW, diacom shows all normal during this process with almost perfect timing advance, integrate and BLM. I only rack-up about 4~6 knock counts during startup and show no retard due to that in Diacom.

Is my engine starving for fuel?
Is my ECM bad?

Got any ideas?

Thanks,
Mark :cry

 

Well crud. I just put an LT1 intake on my L98 and used the MSD Pro Billet Small HEI. I can't get my timing set either. The HEI still has its own advance built into it in addition to what the computer controls. I am thinking that in my case the HEI is adding its timing due to my higher idle speed with my current chip. I see you have a custom chip also. Do you know what your idle is set at?

 

Are you running the same distributor as in my sig? I'm running the 7730 which used a small diameter setup in camaro. The only thing not stock is my Accel 300+ wired in. Engine surges at idle after warm and timing retards. Vacuum drops from 15hg to 12 or so cold to warm probably has something to do with idle change also. I have a friend who's ECM was bad and it caused timing issues but i'm getting no codes. My idle is set for 850 in the chip. Your base idle (without IAC connected) must be below this in order for the ECM to control properly. Set base idle at least 50 RPM below desired (ECM command) RPM.

Make sure you don't have vac leaks,
Check for proper fuel pressure,
Valve timing set ok,

Beyond those I don't know whats going on with mine, I have DFI and might just change over to check ECM. I friend is getting an ECM today and I may change out and see if thats it. Will let you know.

 

Mark,

I had that problem. I put on a new vibration dampener and it soved the problem. The rubber connecting to two parts of the dampener can slip causing timing problems. There is a real good paper in C4 Tech Tips on the subject with directions on how to change the dampener.

Greg

 

Is your cam chain really old and worn?

 

Dampers new
Distributor pickup wiring confirmed
I have a new belt timing setup

I only have 500 mi on this engine and it has run fine.

UPDATE:

I have found the distributor gear is not properly meshing with the cam gear, it (the dist gear) is riding high on the cam gear. This is due to the block being decked and the manifold sitting higher than normal. I'm having about 3/16" taken off the MSD distributor collar so the gear will sit lower and (after some shimming) properly engage the cam gear (in the center of both gears).

From what i've gleaned, if your cam gear/dist gear do not mesh properly and the dist gear is high on the cam gear, you will get thrusting upward and the 5 mils or so of endplay in the dist will be taken up (bob up and down) and wear out the dist gear.

BTW, the gear was correct for the application.

If this doesn't prove to be the problem, it may be cam walk or off-center cam due to block machining or core shift. Both of which I really don't want to find is the problem. :eek:

Gear Wear description;

The gear teeth on approximately 2/3 circumference are worn thin gradually to a worst point opposite the good side were the tooth is 1/3 width of normal. The wear is full contact top to bottom (of the teeth) over 1/3 the circumference. The opposite side shows normal wear for about 3~4 teeth. Shaft to gear fit is spec, distributor endplay is nominal at 5 mils. On the portion of the gear thats showing normal wear the wear mark is 1/8" in from the bottom with a width of 3/16" indicating deviation from optimum gearmesh point of at least another 3/16". Basically, the distributor must sit lower from current position by 3/16" to properly engage cam gear at lateral center.

All should keep in mind, and by no means am I an expert, but the gearmesh between cam and dist is critical to timing and gear life. I've have been told and believe to be true, if this mesh is not centered the timing can be erratic and of course the gear life will be affected.

Thanks for the replys, I will post an update after I get it up and running.


[Modified by Mark84_L383, 5:28 PM 8/13/2002]