Timing with light off 20* from vacuum

[ojobojo]

I have a 1985 CJ7 with a AMC 258 i6 / 4.2l . A month ago I did the Teamrush thing with new cap and wires. After the mod I set the timing to 9* at 1700 rpm (or whatever it was, I can't remember now). As I understand it, this is the proper way to set timing when your ECM is controlling timing.

Anyway, the timing was set properly and the Jeep ran well. Last weekend I did the Nutter bypass. Timing seemed way off at 8* so I timed it with a vacuum gauge instead. This weekend I set timing again after fixing an intake manifold leak. The Jeep barely ran when I set it at 8* so I set it by vacuum again. Ran great. Just for grins I used the advance knob on the timing light (a cheap Harbor Freight) to see just how far off it is -- it's exactly 28* btdc, or 20* before where it should be.

So I suspect the timing light is henky, but, before I go buy another I thought I'd ask you guys if you had any ideas what might be going on. It's running great the way it's set now. In fact, it's never been better.

Sent from my SM-G920V using Tapatalk

 

[Jimbos76cj]

I have a 1985 CJ7 with a AMC 258 i6 / 4.2l . A month ago I did the Teamrush thing with new cap and wires. After the mod I set the timing to 9* at 1700 rpm (or whatever it was, I can't remember now). As I understand it, this is the proper way to set timing when your ECM is controlling timing.

Anyway, the timing was set properly and the Jeep ran well. Last weekend I did the Nutter bypass. Timing seemed way off at 8* so I timed it with a vacuum gauge instead. This weekend I set timing again after fixing an intake manifold leak. The Jeep barely ran when I set it at 8* so I set it by vacuum again. Ran great. Just for grins I used the advance knob on the timing light (a cheap Harbor Freight) to see just how far off it is -- it's exactly 28* btdc, or 20* before where it should be.

So I suspect the timing light is henky, but, before I go buy another I thought I'd ask you guys if you had any ideas what might be going on. It's running great the way it's set now. In fact, it's never been better.

Sent from my SM-G920V using Tapatalk

Are you removing and plugging your vacuum source before setting the timing?

Are you running manifold or ported vacuum? If you unplug the hose and the jeep starts to stumble or there is vacuum on it you are running manifold vacuum. If no stumble or no vacuum your on ported

I run my AMC 258 i6 / 4.2l off manifold. I set it at a base of 8 and when the vacuum is hooked up it goes to 23.

When you set it by vacuum the higher the timing the higher the vacuum but at a certain point it becomes to much to start the the jeep and you get pinging and detonation. I've tried to set mine a few times like that but it never works out well (Pulls a ton of vacuum but off idle is bad). I always end up setting my timing with a light and carb with vacuum.

 

[ojobojo]

Are you removing and plugging your vacuum source before setting the timing?

Are you running manifold or ported vacuum? If you unplug the hose and the jeep starts to stumble or there is vacuum on it you are running manifold vacuum. If no stumble or no vacuum your on ported

Thanks for the thoughtful reply Jimbo. I tee'd it into the ported line on my Carter BBD as per the Nutter instructions. Yes, I removed the vacuum line from the distributor while setting timing.

Also, I didn't mention it but idle was at 680 while setting timing this time.

I run my AMC 258 i6 / 4.2l off manifold. I set it at a base of 8 and when the vacuum is hooked up it goes to 23.

That's interesting, just about the same advance I have. And it runs well, I assume?

When you set it by vacuum the higher the timing the higher the vacuum but at a certain point it becomes to much to start the the jeep and you get pinging and detonation.

Isn't this the reason you're supposed to use ported vacuum?

I've tried to set mine a few times like that but it never works out well (Pulls a ton of vacuum but off idle is bad). I always end up setting my timing with a light and carb with vacuum.

The odd thing is, despite the fact that my timing says it's 28* BTDC it's running great. I find it hard to hear anything in there but i dont hear any ping. I'm confused.





Sent from my SM-G920V using Tapatalk

 

[Lumpy Grits]

Plug the v'line to the dizzy and check your time'n at idle rpm(650-750rpm).
Make a note of it, and motor on since you say she's run'n good.
Don't 'fix' what ain't broke-------
LG

 

[Hedgehog]

I use the very same timing light. Mine is accurate. The dial could be off on yours. I check mine by setting it on "0" and put some * of advance in, say 8*. Then I set the light to 8* and it should read as "0". One matches the other every time. Advice - The dial moves FAR to easily, use tape on the dial to hold it still.

A hot rod buddy of mine used to turn the dist. up slowly. a few degrees at time until the engine would ping or start making noise under load, then he's back it down a few degrees and call it good.

I'm surprised at how often it appears that the timing mark is off on various engines. I wonder if 40 or so years is about the service life of our harmonic balancers.

 

[ojobojo]

Grits, are you saying I should set timing with the vacuum line attached?

Hedgehog, That's a great way to check the advance feature of the light. I've always been careful about making sure it's set at 0. I'd believe the balancer being off, and I should check for that, but it worked correctly just a month ago. That's what makes it so odd. I did hit my finger on the fan while setting up the carb...maybe that made it slip?

Sent from my SM-G920V using Tapatalk

 

[Hedgehog]

Cutting your hand completely off wouldn't make a balancer/timing mark slip. My friend Bill has a 3/4 ton ford with a 351 that never had the power my Bronco had. His balancer went bad. After replacing it they found his timing off by over 10*. His truck has MUCH more available power now. I'm sure the balancer slipped a little at a time for quite a while. Engines torque up and down fairly rapidly all the time. A little slip here a little slip there ..... If your balancer is giving up a month can be a long time for an engine.

 

[Jimbos76cj]

Thanks for the thoughtful reply Jimbo. I tee'd it into the ported line on my Carter BBD as per the Nutter instructions. Yes, I removed the vacuum line from the distributor while setting timing. To

Isn't this the reason you're supposed to use ported vacuum?

Sent from my SM-G920V using Tapatalk

That was my understanding of it before.. Then did a bunch of reading up on the two and found out they work opposite of each other. Manifold is on at idle and drops as you accelerate.. Then When you settle into a cruise speed it picks back up.

Ported only come in when your accelerating.

So when my jeep is cranking it's not adding any timing so I'm at the base of 8. As soon as it fires up my timing moves up to 23. If you had a ported vacuum motor set that high it would crank at 2: and have a really hard time starting. Then when you give it has the timing will advance even more when it should actually be regarding some to help with detonation under load. Then when you settle into cruise you vacuum drops and your running you base again.

With manifold once it's started it goes to full vacuum. Then when you give it gas the manifold vacuum drops retarding the timing to help with detonation. When you settle back in to cruise speed the manifold vacuum builds and advances your timing again.

The story also goes for emissions the motor needs to be close to TDC to eliminate one of the commons offer gasses. The higher the timing the better the mpg.. (Why your vacuum goes up the further you advance it). Also your motor should run "cooler" with the higher advance. Last full tank I ran through my AMC 258 i6 / 4.2l got me about 14mpg in the city not being afraid of the skinny pedal. My motor is .060 over, big cam, long tube headers, msd ignition with a Taurus fan set up. I never see over 180 except for right before the thermo stat opening.

 

[Lumpy Grits]

Grits, are you saying I should set timing with the vacuum line attached?

Hedgehog, That's a great way to check the advance feature of the light. I've always been careful about making sure it's set at 0. I'd believe the balancer being off, and I should check for that, but it worked correctly just a month ago. That's what makes it so odd. I did hit my finger on the fan while setting up the carb...maybe that made it slip?

Sent from my SM-G920V using Tapatalk

Remove the v'line and plug it, then set timing.
Please confirm that you are attaching the t'light to read off the very front spark plug, correct?
LG

 

[ojobojo]

Plug the v'line to the dizzy and check your time'n at idle rpm(650-750rpm).
LG

This is why I was confused.

Yes, using wire #1.

Sent from my SM-G920V using Tapatalk

 

[Jimbos76cj]

This is why I was confused.

Yes, using wire #1.

Sent from my SM-G920V using Tapatalk

truly if your using ported vacuum Ive never seen a need to pull the hose. If removing or putting the hose back on you have it from a manifold source. Ported pulls no vacuum unless you have the butterflies on the carb open. In the older years the process was to pull the vacuum because they ran off manifold. Then when the emission laws became more strict they change to ported.

 

[Jimbos76cj]

truly if your using ported vacuum Ive never seen a need to pull the hose. If removing or putting the hose back on you have it from a manifold source. Ported pulls no vacuum unless you have the butterflies on the carb open. In the older years the process was to pull the vacuum because they ran off manifold. Then when the emission laws became more strict they change to ported.

heres a Jeep Spark CTO switch. One line is manifold, One is ported and the 3rd goes to the distributor. When the motor is started it runs odd manifold, once it heats up it switches to ported (I believe thats the order) Again thats my understanding of how it al lis supposed to work. Like I said before im definitely not the ignition guru. But my motor runs awesome and I know its on manifold.

 

[Hedgehog]

Guys - It's not as if pulling the vacuum line from the advance unit is difficult, nor is plugging the line. The most positive way to be sure vacuum pressure has no effect on timing is to spend the 10 seconds it takes to pull the line.

 

[ojobojo]

It's clear that pulling a ported line has no effect on the idle like pulling a manifold line does. It's easy enough to do, however, that I will continue to pull the line when I set timing.

The Jeep is running like a top now. Idle is rock solid at 680 and I tuned out the last of the backfiring by richening up the carb a lot.

There's a port that's open on the cat because the downstream check valve in the pulse system rotted away. As a result, it sounds like it's got a hole in the exhaust but it's tolerable for now assuming I can run it that way. As I understand it the pulse air doesn't work without the computer anyway. I did plug the port where the pulse air hose hooked to the air cleaner.

I think I'm going to drive it like this for a while. Thanks guys.



Sent from my SM-G920V using Tapatalk

 

[Hedgehog]

Mine doesn't have a computer. The air pump works on vacuum.

 

[ojobojo]

Mine doesn't have a computer. The air pump works on vacuum.

If I'm not mistaken we might have different systems. Mine is like this....

http://home.sprynet.com/~dale02/pulseair.htm

"When it feels like it, the computer actuates the vacuum solenoid which actuates the air valve,..."

I'm guessing mine is inop since I did the nutter....I'd like to know more about this, however, since I'm going to have to do something about the hole in my cat eventually. Yours has an air pump?

Sent from my SM-G920V using Tapatalk

 

[Hedgehog]

Yep yours is different. The systems on both my '75 304and it's replacement the '82 360 are virtually identical. Sorry for the confusion.

You need to fill out your vehicle information. It helps in all of these discussions.

 

[ojobojo]

You need to fill out your vehicle information. It helps in all of these discussions.

Yeah, kind of a sore subject. Can't get in to your forum with the web version and Tapatalk sucks.

Sent from my SM-G920V using Tapatalk