O.K. Here's the deal. Discovered yesterday the timing on my 88 T/A likes to jump around a little. At idle, from about 6 deg to about 10 deg- continuously variable.
Today, I started it up with the timing wire disconnected, it started idling at about 1200-1500 rpm, then dropped to about 500, all the while remaining ROCK SOLID, not varying even 1 deg. Then, I revved it up a little bit- ROCK SOLID- then revved it to about 3000- Then the bastard started jumping all over the board- at idle or rpm- dancing around all over the place. It never really calmed down after that. It seems to jump up to about 12 deg when I rev it up and comes back to around 6 deg @ idle.
New:
- MSD coil
- MSD heli-coil wires
- MSD cap/ rotor
- O2 sensor
- Timing chain/ sprockets
- Checked the plugs- good
- Checked the TPS- good
It has been suggested that it may be the HEI module- has anyone ever had a problem when it's running- I hear that it works- or doesn't work. Or it craps out when it's hot. I have this prob. hot or cold.
Also what is an ESC- isn't that the same thing as the HEI module?
Lastly, It hasn't thrown any codes at all, and I checked everywhere for vacuum leaks, can't find any. I even replaced the intake manifold gaskets just for fun. Sorry this is so long, I'm at my wit's end and starting to think about carburetors - YUK!!!!
Thanks,
Jeff

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88 Trans Am 305 Auto Red/Silver, MSD coil,wires, ported plenum, gutted airbox, TB bypass, comp cams 08-408-8, everything else stock

 

Seems like the control module or the PU coil.
The EST is not the same thing and the control module, the EST controls spark retard. I'm not sure if it would cause issues as you describe...my understanding of the EST is that it sends the signal to the ECM interpeted by the knock sensor to retard timing, and the only way to get the spark advance back is to shut the engine off and restart it.

It seems to me like you're picking up more of a miss-fire. The module is supposed to have some advance capabilities in itself, I think, for failure issues. It could be going to it's "advance" and then dropping off, or the PU coil could could have bad windings/corroision, causing erractic spark timing.

There is one other thing related to ignition fire, that's the reluctor (star shaped thing above the PU coil). I believe the relation with the reluctor and the PU coil set the dwell cycle.

 

Thanks, Mike. I forgot to mention, I replaced the pickup coil. I guess I'll replace the reluctor- it's probably cheap enough.
Any other ideas out there?

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88 Trans Am 305 Auto Red/Silver, MSD coil,wires, ported plenum, gutted airbox, TB bypass, comp cams 08-408-8, everything else stock

 

Just FYI on the reluctor, everybody that's posted they needed to replace one, could see physical damage to it.

Good luck.

 

If you disconnect the timing wire the timing should be DEAD FLAT regardless of RPM. 6* at idle, 6* at 3000, 6* at redline. If it's jumping around even with the timing wire disconnected then the problem is UNDER THE DISTRIBUTOR CAP.

But before you freak and start swapping in new parts try using a different timing light. They get flaky, too, sometimes.

 

An interesting thought.. The car has been doing this just after swapping out the peanut cam. I noticed that the new cam (in my sig) had quite a bit of endplay. It seemed to be about 1/8". I called the Comp cams help line and the guy said " don't worry about end play at all, it's a roller cam". Could endplay be causing this problem at all? the new cam is exactly the same length as the old one though. Wouldn't there have to be a HUGE amount of endplay to cause a 6 deg. variation in timing?
Thanks,
Jeff

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88 Trans Am 305 Auto Red/Silver, MSD coil,wires, ported plenum, gutted airbox, TB bypass, comp cams 08-408-8, everything else stock

 

I've only taken apart one roller block before, so I'm far from an expert, but I seem to recall the cam retainer plate being about 1/8th or 3/16th of an inch thick?

You sure the guy from comp said that? Sure doesn't seem right, what's to keep the cam from walking? Roller cams have no ***** ground on the lobes, and of course the rollers on the lifters are flat. Just doesn't seem right to me.

Hmmn, seems the BBS does not like the word s l a n t ?

[This message has been edited by 8Mike9 (edited September 20, 2001).]

 

Mike, it didn't seem right to me what he said, either, but you wouldn't believe how hard it was to find info on installing a roller cam. Simple questions as: Do you have to use break-in lube? , do you have to break the cam in? no one knew the 'end play' thing. The only thing I kept finding in print was on non-roller cams. Yes the retainer plate is about 1/8" thick. The sprocket keeps the cam from walking backwards, and the plate keeps it from walking forwards (there is no wear on the plate).

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88 Trans Am 305 Auto Red/Silver, MSD coil,wires, ported plenum, gutted airbox, TB bypass, comp cams 08-408-8, everything else stock

 

Ok, I checked the timing light today on another car, and the timing was solid with the timing spout disconnected. Looks like my timing is moving around !
HEEEELLLLPPPPP!!!!
Thanks,
Jeff

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88 Trans Am 305 Auto Red/Silver, MSD coil,wires, ported plenum, gutted airbox, TB bypass, comp cams 08-408-8, everything else stock

 

You didn't say if you checked the gear on the distributor. Roller cams need a special dist. gear (you should have stock) and not all timing chains are created equal, what brand did you use.

[This message has been edited by ZZ3tpichevelle (edited September 20, 2001).]

 

I had a similar problem on my 87 vett. the distributer gear was worn so much that it was sharp and could acutally cut skin! I replaced the entire distributer and no more problem!

 

Hey, Thanks guys, a very good idea. No I didn't replace the dist. gear when I swapped the cam, I just used the same one. Also, I got the stock- type silent roller chain & sprockets. I did notice that there is some play when I turn the rotor back and forth, but could this be the cause of the 6 deg. advancing of the timing at 3000 rpm, or just the wandering timing?

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88 Trans Am 305 Auto Red/Silver, MSD coil,wires, ported plenum, gutted airbox, TB bypass, comp cams 08-408-8, everything else stock

 

I would say if you can move the rotor back and forth you may have found the problem.(dist gear) Some play is normal though.Use GM# 10456413 melonized gears for steel roller cams(some may argue that Comp cams don't need special gears, but look at it this way $20 gear or $200 cam, you choose) I personaly don't like the silent link chain. GM used a single roller on ZZZ-ZZ4 engines. The start of ZZ3 production they went to the silent link, had problems with them, and went back to rollers. That's just my opinion though. You should at least pull the dist. and check the gear. Also just for info GM# 12371043 is the single roller timing chain kit.

[This message has been edited by ZZ3tpichevelle (edited September 21, 2001).]

 

Thanks, ZZ3. I used the silent chain & sprockets 'cause that's all that was available at such short notice (long story). I'll change the dist. gear ASAP and see how that works. I appreciate all the answers on this, everyone is so helpful.
Thanks again,
Jeff

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88 Trans Am 305 Auto Red/Silver, MSD coil,wires, ported plenum, gutted airbox, TB bypass, comp cams 08-408-8, everything else stock

 

Like you said, roller cams have no taper ground into the lobes. Aftermarket set-ups have to use a cam button or other retainer to hold the cam still. 1/8 of an inch of endplay would definitely alter the distributor to cam gear mesh.
I'm not familiar with the stock set-up. What holds the cam in the rear of the block? Could this have moved / gotten damaged?

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88 IROC with cobbled together (not by me)drivetrain, 86 (?) TPI unit on an '83 305,CE subframe connectors, Edelbrock strut tower brace, polygraphite bushings all around...it handles like a dream, but man is it hard to push!!

 

There is a cam retainer plate that bolts into the block . This ia what keeps the cam from walking forward.

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88 Trans Am 305 Auto Red/Silver, MSD coil,wires, ported plenum, gutted airbox, TB bypass, comp cams 08-408-8, everything else stock

 

i have seen this problem at work alot. the timing moves around where it wants. what i have seen is the bushings in the distributer are worn and it alows the shaft to move around where ever it wants to. when you tighten the distributer down, you are tighting the housing, the worn bushings inside it let the internal shaft move and result changing timing. hope this helps. just my .02 about what i've seen. oh, and the best way to fix this problem is buy a new distributer. you should be able to take the dist. out and notice alot of free play in it if in fact thats the problem. lil jay

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Wide Open Till You See God...Then Brake