ccdguy

Hi all,

I'm sorry if this question has been answered before, but search did not reveal much. I'm new to the L98 engines, and I was wondering if there is a write-up anywhere on this forum as to how to check base timing, and potentially advance it should that be necessary? I have done this on my old 87 Mustang, but I'm up to speed on the GM L98 engines. Would someone take pity on me and direct me to a decent write up / how to guide? I have a 1987 Trans Am GTA and my suspicion is that the base timing might be off and no where near 6-8 BTDC. I'd love to check it myself... Just need a little help with the procedure. Thank you in advance.

Orr89RocZ

iTrader: (20)

https://www.thirdgen.org/settingtiming

ccdguy

Thank you... This will be of great help.

miamivice

Question, what does unplugging the wire do?

"Disconnect the tan wire with a black stripe that comes out of the harness near the heater box. It is a big weatherpack connector, you can hardly overlook it."

...and what happens if it is not unplugged?

Ransford2987

That prevents the ECM from adjusting your timing, as even under idle it adjusts the timing from base. If you don't unplug it, you won't be able to set the base timing correctly. What you see as 6*BTDC is actually setting the base closer to 7 or 8* ATDC, as the ECM retards the timing, however many degrees it's supposed to at idle.

Orr89RocZ

iTrader: (20)

Yup, that wire is the EST connector and allows ECM to change timing via distributor. Disconnect it allows you to set manual timing at the distributor like you do any carb car. It removes ecm control when disconnected. Just make sure you plug it back in after you are done Car will be a turd if you dont

miamivice

Someone else did a tune up on my car and adjusted timing as he said it was way off (to start).

I am wondering if perhaps he didn't disconnect that wire when he set the timing.

Anyways, the car still runs, but now has a terrible backfire and seems to be running super rich.

Could this be the cause?

Orr89RocZ

iTrader: (20)

It would be good to double check and set to proper timing

Ransford2987

If the timing is way off it might do that. I would think that you're having fuel that doesn't burn off because the timing is too far advanced, but that seems like the timing would be quite a bit off. It's easy to check it if you have a timing light, and takes less than 10 minutes (I had to unbolt the ignition coil to get to the distributor hold down bolt).

vdoggie

does someone have a picture of where this wire is? I looked everywhere!!

Bigfoottpi11

You may have to remove your coil to get to the distributor hold down bolt.

vdoggie

Found it.. didn't work.. I'm pretty sure I need to align the notch on the harmonic balancer with 0 before I actually start the engine in order to check timing, yes?

rusty vango

I would check static timing FIRST.balancers have a nasty habit of being "off" #1 cyl on its compression stroke .both valves closed for that cyl.now check to see if the timing marks on your balancer is at "0". if not the case .well, there is your first problem

junakajun

Hi ThirdGen Members,

I recently got a 1991 RS (V6) Camaro. It seem to be running fine, but one day in the highway it just stopped running properly. I've bee chasing many problems, but I think I found a big one that needs to be addressed first. The base timing is way off (I follow the info in the link in this tread to check). It is almost 20 degrees off before the recommended 10 degree before. I mean, is no where near the timing indicator.

I have tried to move the distributor as far as I can to get the timing closer to spec., but I can't reach the proper timing, because the distributor reaches some sort of end. I'm thinking I need to remove the distributor and rotated a bit so I can then try to adjust the timing. However, I'm not sure how much should I move it, nor the direction I should move it to. Any recommendation of how to proceed. I know I need to be careful as I could completely loose the timing I have now, so I feel better if I had more info on how to proceed properly.

Thanks,
Jun

rusty vango

static time the engine .as in both valves for #1 cyl closed.#1 piston at the top of its compression stroke. now check to see if A your balancer timing marks are correct .B your timing chain is good ,by having the dist. cap off and with a socket on the balancer bolt rock the engine back and forth .the rotor should follow your movements EXACTLY. these steps save a lot of WTF moments good luck and let us know how it went

junakajun

That's a great catch there. Perhaps a bad timing chain would explain why all of the sudden the car started to missbehave. If that's the case I'm surprised the motor runs at all.

I need to figure out how to do some of the things that you just mention. I mean, I know what needs to happen, but I need to figure the details of how to make it happen. At least now I seem to have a plan to try to reach a root cause, instead of trying stuff for the sake of trying stuff. I''ll keep you guys posted.

junakajun

I started with option B as it seem to be the easy one to try first. I remove the distributor cap (the thing that hold the spark plug cables). I then rotated the balancer bolt and looked at the rotor (the thing that holds the electrode inside the cap). When I change the movement direction, there is a delay between the rotor and the balancer bolt. So, is this an indication of a problem with the timing chain?

Update:
I found a few YouTube videos about the effects of a worn out timing chain. This resembles a lot what I'm seeing with my engine. Per the video, the Base Timing could be affected by the timing chain (~1:10 on first video). Video Links below: