Need some help with a timing issue

[MTMike]

The truck's been running funny lately so I went and hit it with a timing light again and it's fine at idle, 10-12 deg. BTDC advanced w/ the vacuum advance disconnected. But, as soon as I rev the engine, the timing retards back to between TDC and 4deg ATDC! I don't like the idea of revving it higher than 2500 rpms or so while My head's the engine so I don't rev it way up w/ the light, but it's definatley hurting my performance and gas mileage. When driving the power seems to come back in about 2500 or so, which is, I assume, when whatever's wrong w/ the timing system corrects itself partially and comes back.

Also, when I hook the vacuum advance up and time it, I still get my 10-12 deg. BTDC advance but when I blip the throttle I get an immideate +10-12deg of advance, but at about 1500 rpms or so It still comes back to right about 0 degrees. Also, when I rev it to about 1200-1300 rpms and hold it steady the timing is bouncing all around...... advance fluctuating between 8 and 20 degrees advanced randomly

I'm completely stumped, as is every person I've talked to, including mechanics.

I have the factory HEI Distributor, and yes, I did check to make sure it was tightened down securely. I also new cap, rotor, Summit HEI coil & Summit 8mm plug wires I recently installed.
Any help would be appreciated

-Mike

[ibthumpin]

when you grab the rotor and try twisting it back and forth is there excessive play (worn out gear, worn shaft bushing)??

[MTMike]

Originally posted by ibthumpin
when you grab the rotor and try twisting it back and forth is there excessive play (worn out gear, worn shaft bushing)??

I just went out and was messing around under there and It feels as though there's excessive play..... probably 15-20 degrees total (7-10 each direction). I'm gonna have to look around into a new distributor, aren't I?

Thanks for the quick reply!!!!!!!!

-Mike

[ibthumpin]

I wouldn't say for sure that 15-20 deg. of "slop" is excessive - there will be some movement of the rotor. It might be something to look into tho

[MTMike]

Originally posted by ibthumpin
I wouldn't say for sure that 15-20 deg. of "slop" is excessive - there will be some movement of the rotor. It might be something to look into tho

I've run out of options. This is the last thing I can try to see if it fixes the problem. And I'm guestimating at the 15-20. It could be more. But when I spin it backwards and put slight force on it it starts to lift up slightly before it locks. It does feel really loose too.

I'm gonna go to the junk yard on Tuesday and see if I can pick up a decent destributor for $20-30 and see if thats it or not.

Any other suggestions? I've tried everything!

-Mike

[MTMike]

OK, the junk yards wanted 50-75 for a used one, and only 2 of the 5 junk yards within 30 miles even had one, and those 2 only had 1 each, one for $50, one for $75. So I hit eBay, and won this bad boy!!!!

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=1871829052

That module is worth the $40 in itself, so if it's as nice as he claims it is, it's a killer deal!

I'll let yall know how it turns out when I get it installed

[ibthumpin]

hey good deal!
I'll be interested in knowing if it fixes the prob.

[MTMike]

Well I got the new distributor in today. WOW!!! it idles so smooth, and has alot more mid & high range power..... BUT the timing problem just isn't as bad, but it didn't completely fix it. The timing still comes back between 1000 and 1500. After that though, it starts to climb up earlier

So it's got me thinking..... I wonder if it's the timing chain? If there's alot of slop in the timing chain would it possibly cause it to do funky stuff like that?

But the new distributor did make a big difference in how long it came back for, and how much, but it's still doing it

Any other suggestions? Could it be the Timing Chain do you think?

Thanks!

-Mike

[ibthumpin]

Certainly wouldn't hurt to check it out especially if the motors got many miles on it. To me, tho, it would seem that if the chain was bad (excess slack), timing would be jumping all over, with no real pattern. I dunno.

[MTMike]

Originally posted by ibthumpin
Certainly wouldn't hurt to check it out especially if the motors got many miles on it. To me, tho, it would seem that if the chain was bad (excess slack), timing would be jumping all over, with no real pattern. I dunno.

Thats what it did with the old distributor...... It doesn't fluctuate now, it adjusts itself gradually now.

Would a vacuum leak cause that to happen?

The only other thing I can think of would be an excessively worn cam gear (the one that drives the distributor)

I'm at my wits end with this thing

It is running alot better though, so i'll just deal with it for a while longer

Thanks!

-Mike

[MTMike]

Well spank my ass and call me stupid.....

The truck is fine, the ignition timing is fine. I just forgot to remove the vacuum advance when I checked it that last time. Everythng's fine

The distributor did fix the problem after all.

Time to go have a few beers :)

Thanks for you help & support, IB.

-Mike

[ibthumpin]

hey, glad I could help a little bit........... :D

[MTMike]

well f*ck my truck.

It was just a fluke...... the timing problem is back in its entirety, and it's not in the igntiion system. I ran out to the store and it had no power. When i drove it earler it was flying. And I didn't TOUCH the distributor. Hit it with a timing light...... it's back to square 1.

time to get rid of this old beast. I've had it

it must be the timing chain or the cam gear.

I give up.

:mad: :mad: :mad: :mad: :mad: :mad: :mad:

-Mike