Engine Timing Question

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Topic author
MReno
Posts: 158
Joined: Sun Mar 03, 2019 6:39 pm

Engine Timing Question

Post by MReno »

So I have a 1989 GW that now has an Edlebrock 1405 or 1406 4bbl carb and most of the emissions hoses & components have been removed. I can get the engine running pretty good at a higher rpm but at idle it dies out, however I am not sure the engine timing is set correctly. Not being an engine guy, does the 4bbl change what the factory timing should be set at? If so, how can I determine how it should be set? I did complete a carb-rebuild, so I know that is is good shape.

Once the engine is running, with manual choke wide open, I have to keep the throttle de-pressed a bit (@2500-3000 rpm I would guess) to keep it running; however, when I add acceleration quickly the engine runs smooth, but at some point it will backfire from carb and then engine will shut off; likewise, when I reduce throttle to idle, the engine will shut off.

Any thoughts on where timing should be and it this could be the cause of the symptoms I stated above?
1989 Jeep Grand Wagoneer
Newbee to owing an old classic that needs some work, but she runs!

will e
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Re: Engine Timing Question

Post by will e »

Howdy. A bit more background on what led up to the symptoms would be helpful. Did you recently add the 4bbl carb? Was it running okay before?

Typically, when you change one component like the carb, you need to adjust the timing. However, I would not expect a swap from one carb to another to require a change in timing for idling, or at least to be able to idle.

You mention all of the emissions equipment has been removed. Your symptoms sound similar to a vacuum issue. Have you confirmed that all vacuum ports are either connected or plugged? You mentioned the emissions is all disconnected, do you still have the PCV system connected?

If you've confirmed no vacuum leaks and the PCV is connected the next thing I would check is how your distributor vacuum advance is connected. Is it connected to ported or manifold vacuum? If it was previously connected to manifold vacuum it would have been getting vacuum at idle and this would advance the timing at idle. If it was moved to ported vacuum it lost the vacuum signal at idle and would cause the timing to be less advanced.

Do you have a timing light and vacuum gauge?

Use the timing light to set your initial timing close to factory. This should work fine to get the timing in the right place for the jeep to idle, even with a 4bbl. If it won't idle, it's probably not a 'timing' issue.

Once you can get the engine to idle and run with the initial timing set to factory you can tweak it to work. A classic approach is to connect the vacuum gauge to manifold vacuum. Increase the timing to the 'highest' vacuum. Adjust the idle speed close to where you want it. Then adjust the idle circuit to the best idle vacuum you can get. Adjust the idle to where you want it. Take it for a drive and put a load on the engine. Does it ping?
If it pings, adjust the reduce the initial advance. Adjust the idle speed and circuit to best vacuum again. Then test drive again. If it pings repeat reducing the initial timing a bit. You can do this a couple of times but if you find you really need to retard the initial timing a lot to keep it from pinging AND it no longer idles smooth you will need to look at re-curving the distributor (or limiting total advance). I doubt this will be the case.

Ideally the initial timing would be set to best vacuum and the distributor would be curved to avoid pinging, this would get the very best all around performance but if you end up backing off the initial timing a bit, it won't really matter in any noticeable way.

If after setting the initial timing it doesn't ping under load you can advance the timing a bit until it does and then set idle speed and idle circuit. If you find this is smooth enough then you have found a pretty sweet spot.

Once it is how you like... Check the timing with a timing light so you know your new 'baseline' timing. Do it with and without the vacuum advance connected. Record the idle speed and vacuum readings too.
81 Waggy 'WILL E' Retired
82 Cherokee WT - SOA/SF/high steer/Alcan springs/agr box/Borgeson steering shaft/AMC 401/performer/holley TA/HEI/BeCool/727/ALTAS (2.0/2.72/5.44)/D60 Snofighter(Yukon Zip,hubs,stubs,4.56)/14 Bolt (FF,BF shave, Discs, ARB,Artec Truss)/MTR 37X12.5/Corbeau XRS Baja & 5 point retractable harness/Hella Aux lights/tuffy console/killer32 sliders/Evil Twin bumpers, rack and roll cage/WARN 8000/TT Fabworks steering brace/dual batts/custom TC skid plate/ARB fridge

Topic author
MReno
Posts: 158
Joined: Sun Mar 03, 2019 6:39 pm

Re: Engine Timing Question

Post by MReno »

Will e,

Thanks for the detailed reply. In all honesty, I really have not begun to look at the emissions removal components and if what is remaining is properly routed and plugged. Where could I find this information so I can trace what I have vs. what I should have? Once I can confirm this is correct, then I can jump in to tweaking. I do not have a timing light or a vacuum gauge, so I would need to rent or obtain as a loaner tool.
1989 Jeep Grand Wagoneer
Newbee to owing an old classic that needs some work, but she runs!

ArchitectJS
Posts: 293
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Re: Engine Timing Question

Post by ArchitectJS »

MReno wrote: Fri Jan 24, 2020 1:30 pm I do not have a timing light or a vacuum gauge, so I would need to rent or obtain as a loaner tool.
buy one on ebay. shouldn't need to spend a lot. You will need it.
1982 Cherokee, base (Bumppo)
AMC 258 / A727 - AMC 20 / NP208
Holley Sniper with Hyperspark
3" Rough County Lift

letank
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Location: SF bay area

Re: Engine Timing Question

Post by letank »

As said above, get a timing light with advance dial... and better splurge and get one with the rpm, and a vacuum hand pump, you can connect it as a read only, then test some of your failing systems...

Will E nailed it, but for your infos, the stock timing 12 degrees is a good start... 14 is better, not too sure of your location, Reno... you can go 16... as for the poor idle, try to richen the mixture a bit, 1/4 turn... may be you are running a bit lean, when you said that acceleration smooth things a bit, there is an added shot of gas... the backfire can be many things...
Michel
74 wag (349 Kmiles... parked, next step is a rust free body)
85 Gwag (229 Kmiles... the running test lab)

will e
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Re: Engine Timing Question

Post by will e »

MReno wrote: Fri Jan 24, 2020 1:30 pm Will e,

Thanks for the detailed reply. In all honesty, I really have not begun to look at the emissions removal components and if what is remaining is properly routed and plugged. Where could I find this information so I can trace what I have vs. what I should have? Once I can confirm this is correct, then I can jump in to tweaking. I do not have a timing light or a vacuum gauge, so I would need to rent or obtain as a loaner tool.
Generally all of the vacuum ports are either on the intake manifold or on the carb. All ports on the manifold will be 'manifold' vacuum and will he high at idle. The vacuum is created because the carb is restricting the air flow that the engine is trying to take in. The carb ports are a little bit more complicated. There are only two kinds, 'manifold' and 'ported'. Manifold ports on the carb will have the same vacuum signal as the ports on the actual manifold. 'Ported' are located earlier in the air delivery circuit and will only show vacuum above idle. Both actually show ZERO vacuum at wide open throttle.

There is a BUNCH of info out on the web about HOW it works. Do a bit or research because knowing how it works is powerful.

There is also a very long age old argument if 'manifold' or 'ported' vacuum is best for a distributor advance. And the answer is 'it depends'. Our later model jeeps had very complicated vacuum systems to route either manifold or ported vacuum depending on various engine inputs. This is rather complicated and, in my personal opinion, of little overall value. All of my old cars are routed to either manifold or ported vacuum from the distributor.


Go ahead and buy a timing light with an advance dial. What you do is turn the dial until the timing light is firing right at TDC and then you know the offset. Most of these also have an RPM feature, which is nice. You can get a really cheap vacuum gauge for about 10 bucks. Accuracy isn't important in the reading, consistency is. So if its a bit off from actual vacuum it's no big deal to you because you are looking for 'highest' vacuum that gauge reads, not a specific number.
Last edited by will e on Fri Jan 24, 2020 8:02 pm, edited 1 time in total.
81 Waggy 'WILL E' Retired
82 Cherokee WT - SOA/SF/high steer/Alcan springs/agr box/Borgeson steering shaft/AMC 401/performer/holley TA/HEI/BeCool/727/ALTAS (2.0/2.72/5.44)/D60 Snofighter(Yukon Zip,hubs,stubs,4.56)/14 Bolt (FF,BF shave, Discs, ARB,Artec Truss)/MTR 37X12.5/Corbeau XRS Baja & 5 point retractable harness/Hella Aux lights/tuffy console/killer32 sliders/Evil Twin bumpers, rack and roll cage/WARN 8000/TT Fabworks steering brace/dual batts/custom TC skid plate/ARB fridge

Topic author
MReno
Posts: 158
Joined: Sun Mar 03, 2019 6:39 pm

Re: Engine Timing Question

Post by MReno »

Great info Will E. Thanks. I will work on reading up on the vacuum system.
1989 Jeep Grand Wagoneer
Newbee to owing an old classic that needs some work, but she runs!

Topic author
MReno
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Joined: Sun Mar 03, 2019 6:39 pm

Re: Engine Timing Question

Post by MReno »

I guess knowing what smog components that are required for the engine to run is most important. This is a vehicle that I will use on occasion and not one that I am trying to run at high performance.
1989 Jeep Grand Wagoneer
Newbee to owing an old classic that needs some work, but she runs!

will e
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Re: Engine Timing Question

Post by will e »

Technically there are no emissions equipment that is required for the engine to run. In the 60's cars didn't even have a PCV system.

But the PCV is probably the most important and most effective and has zero impact on performance.
The EGR system is pretty effective as well and has no impact on performance when you are accelerating.
A lot of the hoses you see are part of a system that captures vapors from either the gas tank or the carb fuel bowls. When the engine is started these fumes are drawn into the engine and are burned. No impact on performance. Keeps the garage from smelling like gas.
There is also a system attached to the air cleaner that diverts the incoming air over the passenger exhaust manifold. This is activated when the engine is cold and allows it to heat up a bit faster by passing warmed up air into the engine. This also aids in combustion when the engine is 'cold'. No impact on performance. Pretty effective, especially in very cold climates.


IMO the complicated A.I.R. system isn't very effective, especially if you have a newer cat converter.

A lot of the other vacuum systems on your late model GW were designed to control vacuum to the distributor based upon engine temp and other conditions. Often times they no longer work and their effectiveness is limited.
81 Waggy 'WILL E' Retired
82 Cherokee WT - SOA/SF/high steer/Alcan springs/agr box/Borgeson steering shaft/AMC 401/performer/holley TA/HEI/BeCool/727/ALTAS (2.0/2.72/5.44)/D60 Snofighter(Yukon Zip,hubs,stubs,4.56)/14 Bolt (FF,BF shave, Discs, ARB,Artec Truss)/MTR 37X12.5/Corbeau XRS Baja & 5 point retractable harness/Hella Aux lights/tuffy console/killer32 sliders/Evil Twin bumpers, rack and roll cage/WARN 8000/TT Fabworks steering brace/dual batts/custom TC skid plate/ARB fridge

Topic author
MReno
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Re: Engine Timing Question

Post by MReno »

What about the vacuum lines that run to the 4X4 switch? I see a green, yellow, and brown small diameter hard hoses that come off the back of the selection switch on the dash, run thru the firewall, and to the engine. Many of these have been disconnected and I definitely want the 4x4 to operate as designed.

I am assuming these are vacuum or air lines, just not sure how they function to engage or disengage the front differential?
1989 Jeep Grand Wagoneer
Newbee to owing an old classic that needs some work, but she runs!

letank
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Re: Engine Timing Question

Post by letank »

MReno wrote: Mon Jan 27, 2020 1:19 pm What about the vacuum lines that run to the 4X4 switch? I see a green, yellow, and brown small diameter hard hoses that come off the back of the selection switch on the dash, run thru the firewall, and to the engine. Many of these have been disconnected and I definitely want the 4x4 to operate as designed.

I am assuming these are vacuum or air lines, just not sure how they function to engage or disengage the front differential?
the front diff is not connected to a vacuum control switch that was from 80 or 81 until Y84.

the TC is controlled by the vacuum stored in the firewall ball, here is a pict of the firewall for the 85, the later years are similar

Image
Michel
74 wag (349 Kmiles... parked, next step is a rust free body)
85 Gwag (229 Kmiles... the running test lab)

will e
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Re: Engine Timing Question

Post by will e »

In michel's picture the 'firewall ball' is on the left. You can see the T connector and a white 'disc' looking thing below. That disc is a check valve that will allow the vacuum to be created in the ball but when the engine manifold is at zero vacuum (usually Wide open throttle) the check valve keeps the vacuum from being released. This is done so that some of the components that are vacuum operated don't turn off/on/off depending on the engine vacuum. I hope this helps.
81 Waggy 'WILL E' Retired
82 Cherokee WT - SOA/SF/high steer/Alcan springs/agr box/Borgeson steering shaft/AMC 401/performer/holley TA/HEI/BeCool/727/ALTAS (2.0/2.72/5.44)/D60 Snofighter(Yukon Zip,hubs,stubs,4.56)/14 Bolt (FF,BF shave, Discs, ARB,Artec Truss)/MTR 37X12.5/Corbeau XRS Baja & 5 point retractable harness/Hella Aux lights/tuffy console/killer32 sliders/Evil Twin bumpers, rack and roll cage/WARN 8000/TT Fabworks steering brace/dual batts/custom TC skid plate/ARB fridge

sirrus
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Re: Engine Timing Question

Post by sirrus »

Not to hijack the thread, but is there a diagram for 4x4 switch and TC vacuum motor lines (without front axle disconnect) anywhere? With line colors maybe?

I noticed that red hard vacuum line (front facing side of motor) is loose on mine, but I don’t understand where it goes - on 80-81 with axle disconnect it would go to front axle vacuum motor, but what does it do on later vehicles?
Sometimes we reinvent the wheel not to have more wheels but to have more inventors

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Topic author
MReno
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Re: Engine Timing Question

Post by MReno »

All, thanks for the reply and the photo. I have looked thru my Master Repair Manual (3,000 pages) and cannot find any detail on how the 4x4 SelectTrac system vacuum lines should run. On my vehicle, the photo above is accurate, however I believe I have a Green, Yellow, and a Brown hard vacuum line coming from the SelectTrac switch on the lower dash, but cannot seem to find where the Brown line is to run to in the engine compartment?

I am trying to confirm that my 4X4 drive works thru the SelectTrac switch on the dash. Prior to fiddling with this, when I shifted the SelectTrac switch to 4w, no lights on the dash lit up, so I began looking at the lines running out the back of the switch that I then traced to the engine compartment. There I found that the yellow vacuum line was disconnected. When reconnected, the dash light would now light when the switch was flipped to 4w. However I am unsure about the brown vacuum line and where that goes, however I suspect it goes to the differential, or whereever the drive shaft engages the front axle. Does this sound correct?
1989 Jeep Grand Wagoneer
Newbee to owing an old classic that needs some work, but she runs!

will e
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Re: Engine Timing Question

Post by will e »

You might start a new thread on the vacuum lines and 4wd engagement. It will broaden the responses. I have no experience with the vacuum operated 4wd systems so I can't help. Sorry!
81 Waggy 'WILL E' Retired
82 Cherokee WT - SOA/SF/high steer/Alcan springs/agr box/Borgeson steering shaft/AMC 401/performer/holley TA/HEI/BeCool/727/ALTAS (2.0/2.72/5.44)/D60 Snofighter(Yukon Zip,hubs,stubs,4.56)/14 Bolt (FF,BF shave, Discs, ARB,Artec Truss)/MTR 37X12.5/Corbeau XRS Baja & 5 point retractable harness/Hella Aux lights/tuffy console/killer32 sliders/Evil Twin bumpers, rack and roll cage/WARN 8000/TT Fabworks steering brace/dual batts/custom TC skid plate/ARB fridge
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TeaBag
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Re: Engine Timing Question

Post by TeaBag »

I'f the 89 is the same as the 91 then you should have 2 vac lines that run from the switch on the dash to the transfer case. The 2 lines are used to "pull" a lever on or off to engage your 4wd. There is a vacuum driven actuator on the transfer case that moves the lever. The switch sends vacuum to one hose at a time based on what you select (2wd or 4wd). If I remember correctly, vacuum is only used to move the lever. It doesn't hold it in its position. So if vacuum is lost, the transfer case lever remains in the last position selected.
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