Ignition woes - help please!

[custmfxwg]

Hi Folks,

Sorry for the long initial posting, but I wanted to get as much info out as I could up front.

I could really use some help tracking down what's up with my jeep! Thanks in advance.

Jeep: 1986 CJ7 , AMC 258 i6 / 4.2l , T-5 , Motorcraft Distributor with big cap adapter and brass contacts, MSD 6AL 6420 ignition, MSD Blaster 2 coil 8202, Timing set at 10 BTDC. Rebuilt Motorcraft 2100 Carb with spacer, single fuel filter (screws into carb).

All ignition and fuel items are new: dizzy, cap, rotor, plugs, plug wires, ignition box, coil, carb, vacuum lines, fuel pump, fuel filter.

Here's the situation: Jeep idles fine, most of the time. When I try to drive it I make it sometimes 200 feet, and other times 1/4 mile, and it falls on its face (stumbles and misses and sometime dies). If I stop and let it idle it runs fine, again, most of the time. When it's not idling fine its stumbling and missing.

History: About 1 1/2 months ago I drove it about 3 miles to pick up my daughter from school. While waiting in the parking lot it began to idle rough. By the time I made it back to the house it would barely run. I thought maybe water in the fuel, but have since ruled that out. When the issue started I had less than half a tank - I filled up with fresh high test and also added some iso heet without any change in the symptoms.

At the time it had a GM HEI dizzy on it from previous owner (I've owned the jeep about 1 1/2 years). I replaced plugs, cap, rotor, and coil. No change in the symptoms.

Replaced the fuel filter - no change.

It also had the carter carb on it. I removed it and replaced it with a MC2100 that I rebuilt, along with a new fuel filter. It ran fine....for about 15 minutes and then started acting up - no change. I used the same setup for the vacuum lines in the attached pdf, but am using a single feed fuel filter instead of the single in - two out. For some reason it would not run with the original jeep filter.

Yesterday I swapped out the HEI for the motorcraft and installed the MSD box (Previous owner had removed the ECM).

Once I set the timing - tried both 8 BTDC and 10 BTDC - it idled fine. So much better than previously that I thought I had the problem solved. I went for a test drive and only made it 200 feet down the road!

I've read that a bad ground could cause this same issue, but I don't know where to check or what I'm looking for. Motor to chassis seems ok as does batter to chassis, but I haven't replaced the wires or thrown a meter on them.

Any ideas or thoughts?

Thanks,
Curt

 

[jeffgtoman]

I think a fuel system test is in order. Hook a fuel gauge up at the carb and see what your fuel pressure is when it acts up. Also, start the engine with the gas line off and stuck in a container. See if the fuel comes out in good quantity. It will probably pulsate but it should be a good shot of fuel at every pulse and not just a spit or dribble.

The way you describe the problem, idling fine but falling on it's face above idle, sounds like fuel starvation to me.

 

[elwood blues]

The first thing that sticks out in my mind is your fuel filter. If you're not running the stock fuel filter, the one with a single in and two out's, have you plugged the vapor return line to the fuel tank? The stuttering engine could be a sign of vapor lock, which is what you could have if you haven't plugged that return line.

I've never heard of a bad ground causing the engine to stutter like that, I wouldn't rule it out, but I don't think that's your cause.

 

[custmfxwg]

Thanks for the replies. The weather is a little nasty here today so I probably won't get a chance to check things out.

One bit of info I forgot to mention that may help is that it doesn't do this all the time. It may take a good quarter to half a mile. The whole while it's accelerating and running fine, and then it stumbles and misses.

I'll check the fuel flow once the weather allows. I did not plug the return fuel line so I'll be sure to do that too.

 

[Torxhead]

Fuel flow seems to be a good place to start, I would suggest checking the fuel lines for any damage. The 5/16" line that comes from the gas tank to the hard line can crack and cause problems. There is the fuel pick up sock inside the fuel tank that can be clogged. I would agree with a fuel pressure gauge installed in the line out of the fuel pump. Even a clogged fuel tank venting system can cause problems, this can be checked by listening for a hissing noise while removing the gas cap after a good drive.

 

[JR74CJ5]

On your vac lines.

You rand them as shown per your post, did you make sure you are getting ported vac for the distributor vac advance through the cto switch while it's warmed up?

Forgive me if you already know all this, but do you know the function of the CTO switches, how and why they work, and which outputs are ported / manifold vac? do you know the difference there too? have a vac gauge? have you checked the vac readings?

etc.

I think the above recommendations to check fuel delivery, and pressure is also a big possibility.



~ JR

 

[custmfxwg]

Looks like I need to pick up some gauges and do some testing!

I have know idea if my cto valve is working or not, or what it does so please feel free to let me know or where to find the info. The advance is currently connected to the ported vacuum port on the bottom of the carb just below the choke. I've also tried the port in the manifold just above the egr valve with no difference.

What type of readings should I be looking for in both fuel and vacuum?

Thanks!

 

[JR74CJ5]

I'm not an expert (so some others please correct me if this is wrong), but from what I read here's a few basics.

Using a vac gauge like this:

Equus Innova 3620 - Vacuum Gauge | O'Reilly Auto Parts

Ported Vac: Should be at 0 (or very close) during Idol and increase higher when throttle applied (RPMS higher = vac higher)

Manifold vac should be higher at idol and lower as the RPMS increase.

A CTO switch: Basically works like this.

When coolant temp is cold it uses the inner most port "supplied" vacuum and sends that vacuum through the output port (usually the center port is output), and when the coolant reaches "x" degrees, it will switch the the port it receives the vacuum from to the outer supplied vacuum and still sends it through the same output. So, there are two vacuum input ports and one common output port. the temperature is used to switch which input it uses.

If your motor just starts up, it will use the manifold vac for the vac advance on your distributor. This will allow a small amount of advance during the warm up period. Once the coolant is hot enough to "switch" the CTO input, it will be Ported vac instead. (I have heard different though too...)

Your vacuum advance on your distributor should run on ported vacuum when warm. I have read it should ALWAYS run on ported before, and read manifold vac during warm up and ported after as i explained above too. I am not sure which is correct and true and in which circumstances one is better than the other.

Now the cool thing i like about the gauge i posted above is: It also measures fuel pressure in addition to vacuum.

As for readings, I will see what I can find from when i was researching. Off the top of my though:

• Ported vac should read 0 at idle and somewhere between 15-20 inHg when at WOT (wide open throttle and that may be only for the AMC 304 V8. your readings may be different?)
• Manifold should be about the opposite.
• fuel pressure for a MC2100 should be fine at 5-7 psi.

Those, again, are my off the top of my head remembering from 3 weeks ago numbers, and I was looking for numbers for my AMC 304 V8, so yours may be different...

To test if a CTO switch is working properly, You can measure the output port while first stating your jeep and coolant is cold. Get the vac reading, and disconnect the inner supply line while reading it. if it changes and you feel suction from the port you just unhooked (from the switch side, not line side) then move on hook it all back up, and disconnect the outer port line. see if it is sucking (it should not). Now with the coolant warmed up, do the same thing but opposite. there should now be "sucking" with the outer and not inner. then unhook the inner again and ensure it is not still "sucking" as it should be cut off by the switch inside.

Throughout all the above, your guage should be hooked to the output port of the cto switch. And we are assuming i am correct that the inner of the three ports is the cold input, and outer is the hot input.

Like this:

Now since you do (I am assuming) have to pass smog checks, how you hook up all the vac lines may need to be different that i have described above.



I hope I've helped... I'll look for the vacuum links i was reading, and some fuel pressure info links as well and post what i find later today.

And again please, anyone, correct me if any of the above is wrong...


~ JR

 

[bondo258]

Since different ignitions and carbs don't seem to have cleared your problem, I think it's something else, too.

Has a Previous Owner installed an extra fuel filter somewhere beneath the Jeep? Lot's of folks do this, especially if the Fuel gauge doesn't work. (they put a clear one in to check for Air)

Is your fuel Tank currently vented? The lines between the charcoal can, fuel return lines, etc. sometimes get plugged internally. Once that happens folks either disconnect them, plug them, or reroute them, thinking it will fix the problem.

Sometimes the problem seems to go away, and they think the problem is fixed. A few "repairs" like this and you have a barely running Jeep.

Good luck.

 

[IOPort51]

you said you had discarded the possibility of water in the fuel but did you check for junk in the tank or if the filter is clogging. I would rather take a fair decent whooping than drop the tank but if something does not show itself soon I think you should start to think about doing that. The screen /filter in the tank is very fine and the tank is steel and there has been some condensation over the past 30 years so there is some rust in the tank and until you drop the tank you can never get it really clean.

 

[custmfxwg]

Thanks for everyone's comments. Still having problems, but wanted to give a quick update:

...Hook a fuel gauge up at the carb and see what your fuel pressure is when it acts up.

The way you describe the problem, idling fine but falling on it's face above idle, sounds like fuel starvation to me.

I put a pressure gauge on it and am getting 6 1/2 to 7 lbs when it's idling fine and when it's stumbling and it seems to be getting plenty of fuel.

...have you plugged the vapor return line to the fuel tank? The stuttering engine could be a sign of vapor lock, which is what you could have if you haven't plugged that return line.

I plugged the return line and it made no difference.

Fuel flow seems to be a good place to start, I would suggest checking the fuel lines for any damage. The 5/16" line that comes from the gas tank to the hard line can crack and cause problems. There is the fuel pick up sock inside the fuel tank that can be clogged. I would agree with a fuel pressure gauge installed in the line out of the fuel pump. Even a clogged fuel tank venting system can cause problems, this can be checked by listening for a hissing noise while removing the gas cap after a good drive.

I've physically looked at the lines, but haven't tried to blow air through them or anything yet. Don't really want to drop the fuel tank just yet, but it may come to that.

Ported Vac: Should be at 0 (or very close) during Idol and increase higher when throttle applied (RPMS higher = vac higher)

Manifold vac should be higher at idol and lower as the RPMS increase.

A CTO switch: Basically works like this.

When coolant temp is cold it uses the inner most port "supplied" vacuum and sends that vacuum through the output port (usually the center port is output), and when the coolant reaches "x" degrees, it will switch the the port it receives the vacuum from to the outer supplied vacuum and still sends it through the same output. So, there are two vacuum input ports and one common output port. the temperature is used to switch which input it uses.

If your motor just starts up, it will use the manifold vac for the vac advance on your distributor. This will allow a small amount of advance during the warm up period. Once the coolant is hot enough to "switch" the CTO input, it will be Ported vac instead. (I have heard different though too...)

Your vacuum advance on your distributor should run on ported vacuum when warm. I have read it should ALWAYS run on ported before, and read manifold vac during warm up and ported after as i explained above too. I am not sure which is correct and true and in which circumstances one is better than the other.

• Ported vac should read 0 at idle and somewhere between 15-20 inHg when at WOT
• Manifold should be about the opposite.
• fuel pressure for a MC2100 should be fine at 5-7 psi.

Thanks for the great info, JR. You've been a huge help. I have the 5 port CTO switch rather than the 3 port one, but it appears it's not working at all. I don't get any reading at all on any of the ports. The ported line running to the distributor is running 0 at idle and climbs to 15-20 inches like you mention so that part seems correct. I have a manifold port that is currently blocked (it's just above the EGR valve) and it runs as you mention above as well (15-20 inches at idle and drops as RPMs increase).

Since different ignitions and carbs don't seem to have cleared your problem, I think it's something else, too.

Has a Previous Owner installed an extra fuel filter somewhere beneath the Jeep? Lot's of folks do this, especially if the Fuel gauge doesn't work. (they put a clear one in to check for Air)

Is your fuel Tank currently vented? The lines between the charcoal can, fuel return lines, etc. sometimes get plugged internally. Once that happens folks either disconnect them, plug them, or reroute them, thinking it will fix the problem.

Sometimes the problem seems to go away, and they think the problem is fixed. A few "repairs" like this and you have a barely running Jeep.

Good luck.

I've crawled all over and under the jeep - no extra filter to be found. All the lines running to and from the tank appear to be connected to the right places (tank, canister, small plastic canister in the inside rear quarter panel, etc.)

you said you had discarded the possibility of water in the fuel but did you check for junk in the tank or if the filter is clogging. I would rather take a fair decent whooping than drop the tank but if something does not show itself soon I think you should start to think about doing that. The screen /filter in the tank is very fine and the tank is steel and there has been some condensation over the past 30 years so there is some rust in the tank and until you drop the tank you can never get it really clean.

I'm really not wanting to drop the tank yet, but it may come to that.


I've also jiggled every wire I could find with the jeep running fine and the jeep running rough and can't find anything causing it to change.

A bit of info that may or may not help - when it's idling fine I can rev it up just fine without issue. I can hold it at 2000 - 2500 rpms with no problem. It's only when I begin to drive it that the problem comes up and if starts to stumble. I've driven it three times today. The first one I made it 1/4 mile and then didn't think I'd get it back home, the second didn't make it 20 feet. The third close to 1/2 mile.

I'm also noticing an odd smell from the catylitc converter, but only when it's acting up. The O2 sensor isn't connected (no wiring) and the cat has a small hole it in where the return pipe used to go. Any idea if it could be clogged and causing this problem?

I know this is a long post, but I wanted to ensure I tried to hit everyone's suggestions. Still need to check the vent system - and I really don't want to drop the tank.

 

[CJim7]

I'm also noticing an odd smell from the catylitc converter, but only when it's acting up. The O2 sensor isn't connected (no wiring) and the cat has a small hole it in where the return pipe used to go. Any idea if it could be clogged and causing this problem?

...

 

[Torxhead]

That kind of fuel pressure does sound a bit high, it should only be around 4 psi with the return line hooked up, but at least you have a good amount. So you can probably hold off on dropping the fuel tank for now anyway. The small 1/4 fuel return line should be at the 12:00 position for proper operation btw, the fuel return system could have a clog in it also. You should be able to blow thru that return line with the fuel cap off. You mentioned that the O2 sensor not being hooked up, probably also have the computer disconnected, which controls fuel mixture with the oem carb. since you had an hei distributor in it. I was wondering about the fuel mixture running rich, do the spark plugs have black soot on them? that would indicate a rich condition. Which can also ruin a catalytic converter and clog it up.

 

[JR74CJ5]

I'm also noticing an odd smell from the catylitc converter, but only when it's acting up. The O2 sensor isn't connected (no wiring) and the cat has a small hole it in where the return pipe used to go. Any idea if it could be clogged and causing this problem?

...

Not sure about the CTO switch not working correctly, but I think that is a separate issue... Think it's your cat...

Is the cat bolted on or welded? if bolted, unbolt it and if possible, without getting in trouble run around the block. It will be terribly loud... (I like it lol) but may tell you for sure if thats your grimlen.

 

[jeepboy45]

halfway through reading the thread and I thought you might try something simple as driving it with no gas cap.... Would rule out a couple of things. Then when the issue of catalytic converter came up, I'd be going that route... Had a honda accord on a road trip one year, about 700 miles from home, it wouldnt let me go more than a mile or two before shutting me down... Drove screwdriver through it about 20 times... Got me home fine (and loud) and onto the next owner to deal with it.

 

[bondo258]

I'd try jeepboys gas cap idea first.

Question. Does it only stumble under load? Does it stumble while revving the engine in neutral?

Try running the engine off of a Gas can, with fresh gas in it. Just drop a rubber hose in it and connect to intake port of your fuel pump.

Run a return line back to the can.

If this changes nothing, don't bother dropping the tank, or pulling lines.

If it does change something then your Tank has in it, or your return line is restricted.

 

[custmfxwg]

That kind of fuel pressure does sound a bit high, it should only be around 4 psi with the return line hooked up, but at least you have a good amount. So you can probably hold off on dropping the fuel tank for now anyway. The small 1/4 fuel return line should be at the 12:00 position for proper operation btw, the fuel return system could have a clog in it also. You should be able to blow thru that return line with the fuel cap off. You mentioned that the O2 sensor not being hooked up, probably also have the computer disconnected, which controls fuel mixture with the oem carb. since you had an hei distributor in it. I was wondering about the fuel mixture running rich, do the spark plugs have black soot on them? that would indicate a rich condition. Which can also ruin a catalytic converter and clog it up.

Not sure about the CTO switch not working correctly, but I think that is a separate issue... Think it's your cat...

Is the cat bolted on or welded? if bolted, unbolt it and if possible, without getting in trouble run around the block. It will be terribly loud... (I like it lol) but may tell you for sure if thats your grimlen.

Well it's not the cat. Took it off and ran some straight pipe in its place to the muffler. Still doing the same thing.

Read previously about the fuel filter being at 12:00 with the 1/4 return line and had it that way to begin with. Computer is disconnected and and there's no ecm. Plugs look good. Looked good before I changed them out, and I've had them out a few times since this problem and so far they're not soot'n up at all.

halfway through reading the thread and I thought you might try something simple as driving it with no gas cap.... Would rule out a couple of things. Then when the issue of catalytic converter came up, I'd be going that route... Had a honda accord on a road trip one year, about 700 miles from home, it wouldnt let me go more than a mile or two before shutting me down... Drove screwdriver through it about 20 times... Got me home fine (and loud) and onto the next owner to deal with it.

I'd try jeepboys gas cap idea first.

Question. Does it only stumble under load? Does it stumble while revving the engine in neutral?

Try running the engine off of a Gas can, with fresh gas in it. Just drop a rubber hose in it and connect to intake port of your fuel pump.

Run a return line back to the can.

If this changes nothing, don't bother dropping the tank, or pulling lines.

If it does change something then your Tank has in it, or your return line is restricted.

I'll try both the gas cap off and the gas can idea. Hadn't thought of either and that would rule out a lot of things.

Thanks for all the help! I'll let you know what I find out tomorrow.

 

[jeepboy45]

@anyone reading this:
does anyone reading this know if he has a typical ford type brain unit running the ignition???

I've had those completely die, but not quit some of the time...

@custmfxwg:
If it turns out that you do have one mounted on the fender well, look at the back and note whether the resin potting material on the back is beginning to melt or show signs of melting...

THIS HAS GOT TO BE FUEL OR IGNITION RELATED... We're running out of ideas here!!! Sorry that the cat solution didnt fix it... Probably a pain in the *** to do that....

good luck

brian

 

[custmfxwg]

@jeepboy45:

The jeep doesn't have the control module on the fender well - previous owner removed it. I installed an MSD 6AL ignition (model 6420) two days ago when I swapped the HEI for the ford duraspark distributor.

I'll try the gas can and gas cap ideas tomorrow.

I still remember reading something about how a bad ground can possibly cause something like this. I'll keep reading and keep trying things until I figure this out. Pretty soon I'll have a new Jeep with all the parts I keep buying

 

[jeepboy45]

@jeepboy45:

The jeep doesn't have the control module on the fender well - previous owner removed it. I installed an MSD 6AL ignition (model 6420) two days ago when I swapped the HEI for the ford duraspark distributor.

I'll try the gas can and gas cap ideas tomorrow.

I still remember reading something about how a bad ground can possibly cause something like this. I'll keep reading and keep trying things until I figure this out. Pretty soon I'll have a new Jeep with all the parts I keep buying

I'm sorry. I'm a dope!! Totally forgot you already wrote that above... I even took note of it when I read it because that is the setup I have on mine.... Sorry