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Discussion Starter #1 (Edited)
Let me preface this with one statement. I am NOT a mechanic.

1978 Jeep CJ5
304 V8
AMC 20 rear axle
Dana 30 Front Axle
3.54 with LSD rear
Dana 20 Transfer Case

MSD 6420 6AL ignition with MSD Blaster 2 8202 Coil and MSD Distributor cap

I bought this Jeep in April. It has spring over axle configuration running 33 x12.5 x 15 tires.

Ran rough (not stock cam shaft) and a little hard to crank. But ran well.

About 6 weeks ago +- I went 15 miles into town from work for lunch.
Ran fine, idled fine at stop lights, etc. Filled up with gas.

Made it all the way back to work. As I pulled into the parking lot, and coasted toward my spot, it just died when I let off the gas. Didn't even try to idle. As soon as I let off the gas pedal, boom dead.

I was unable to crank it. We pulled it off, and it would start, but ran really rough and would die as soon as I let off the gas. I had my uncle tow me home. I drained the tank and filled with fresh known good gas. Same problems.

It had a Jet carburetor of some kind on it. 2BBL. I took the air cleaner off and had the wife crank it while I hit it with ether. It would start only with ether at this point. Ran really rough and would not idle. Had some kind of white smoke/mist come out of the carb when it died.

I did as much research as I could on this symptom, and came to the conclusion that the needle valve was sticking, which was flooding the carb, and continued to put fuel into carb after the engine died, causing the smoke.

I am 46 years old and have never worked on a carburetor. I wasn't about to start now. So, instead of trying to find a rebuild kit on a carb that was hard to identify (no markings or numbers other than "JET" on it) I decided to get a new carburetor.

I discovered Gronk Performance and heard good things. Motorcraft 2100 / 2150 was recommended, and that was what Gronk provided.

I installed the rebuilt carb and primed the bowl. Cranked right up. Ran like a sewing machine. I've owned new vehicles that didn't run this smoothly.

Got my son and went into town. 15-20 minutes each way. Ran flawlessly for about 45 minutes. Then it died. As soon as I let off the gas.

Replaced the fuel filter. Again. Still not fixed.

Hard to start again. Alternator showed 14+ volts on the gauge when it was running. I thought MAYBE it might be the battery, the New battery didn't solve anything.

Replaced spark plugs. Old ones were filthy and obviously not gapped for the 304. Still not fixed.

Replaced all vacuum hoses. Checked for vacuum leaks on the carb. Took the carb off and replaced all the gaskets and the spacer with fresh/new. Still not fixed.

Replaced all the fuel hoses. I have not replaced the stainless line from the tank to the fuel pump, yet. Still not fixed.

I had a mechanic friend come over yesterday. He replaced the mechanical fuel pump for me. Primed the carb. Cranked right up. Ran smooth again. He helped me adjust the idle screw. Got it to idle and run.

For about 15 minutes. Barely made it out of my driveway before it died as soon as I let off the gas.

So, does anyone know which direction I should go?

Does anyone want to buy a jeep?

This has been posted on jeepforum.com also. Gotten some helpful advice there. Was kinda hoping to get an opinion from a different angle.
 

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Let me preface this with one statement. I am NOT a mechanic.
Sounds pretty hardcore :flipoff2:

I know you mentioned a new fuel pump/venting out the lines and draining the tank. Try pressurizing the tank with an air fitting on the end of your air hose. Not enough to explode the tank but enough to fill it properly. Are your vent lines ran properly from the tank?

I had the same issue on my old 460 once. I could run it off an auxiliary tank at the fuel pump, but it wouldn't start. Put all new lines, drained the tank, new fuel pump, etc but I still couldn't get any fuel to the carb. By pressurizing the tank it starts right up every time since, even after sitting.
 

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Kind of sounds like a heat related issue to me, either vapor locking or possibly losing vacuum once warmed. Tank venting is a good thing to check too; vent lines and even the filler cap itself. I'd probably blow out the hard line between the tank and pump too, just for good measure.
 

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Discussion Starter #4
Try pressurizing the tank with an air fitting on the end of your air hose. How would I go about that? I only have about a 3 gallon Walmart air compressor) Are your vent lines ran properly from the tank?No idea on that one. I have a Chilton's manual for this model/year.
Would a diagram be in there of how it should be?
:grinpimp:
 

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hey for 'not a mechanic' you have tried a bunch of stuff... time to bust out the AAA card and take it to a mechanic.

if you are growing your mechanic skills.. and you have eliminated fuel as the issue (replaced gas, filter, pump and you have gas to the engine.... time to look at electrical and grounding.
 

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coil or ignition module going bad, they can drop out when they heat up and nothing will get them going until they cool off again.
 

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Discussion Starter #7
coil or ignition module going bad, they can drop out when they heat up and nothing will get them going until they cool off again.
I was thinking along those lines. However, the next day after all night cooling off, still won't start or idle.
 

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Might have something g in the tank that’s getting sucked in and only releases once it site. My dad had a semi that they fought for months with random problems. Finally found a small bouquet of flowers in the tank once they pulled it to drain. It got sucked in and would release once the truck sat. Who knows what u have going on, but you are sure dotting your i’s and crossing your t’s for not being a mechanic.........


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Discussion Starter #10
Do you have a tach?

When it dies, and you crank to restart, does the tach sit on the bottom or does it flutter like its trying to read?
Tach hasn't worked since I bought it. I'm not sure if the previous owner hooked it up to the MSD box by mistake, or if it's just busted. It's aftermarket (forget the name) and it's about $350+ to replace. Was never a primary concern. I might have to put it on the list.
 

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Discussion Starter #11
Might have something g in the tank that’s getting sucked in and only releases once it site. My dad had a semi that they fought for months with random problems. Finally found a small bouquet of flowers in the tank once they pulled it to drain. It got sucked in and would release once the truck sat. Who knows what u have going on, but you are sure dotting your i’s and crossing your t’s for not being a mechanic.........


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Well, this is 100+-year-old technology. The internal combustion engine hasn't changed much over the years. It was invented in 1884, I think.

You only need 3 things for this engine to run. Fire, fuel, and air.
The rest is all superfluous. As long as you get those 3 things together in the correct amounts at the right time, then this thing HAS to work.

Now, once you start adding the transmission and transfer case, and axles, and making the whole thing mobile, then you start to make it more complicated. But this problem is stupid simple. And that's what makes it so frustrating.

I'm not some engineer at Morton Thiokol trying to keep the space shuttle in the air. I'm just trying to burn gasoline to create pressure to move a few pistons around a shaft. :mad3:
 

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You need fuel and spark:

Fuel:
You've spent a lot of time on it.

I'd take the gas tank and lines completely out of the equation.

Get a 2 gallon portable gas tank. Run a soft line from the fuel pump inlet into the portable tank.

Do you have a clear fuel filter at the carb, so you can see that gas is flowing?

When it won't start, have you ever checked for spark?

Why have you been focusing so much on the fuel issue, and not the spark issue?

I don't like changing things willy nilly, but this would be a cheap ignition upgrade:

https://www.amazon.com/gp/product/B06XYWBKVP/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1



And wires:
https://www.amazon.com/gp/product/B06XRK7DMT/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1

 

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:grinpimp:
It's as easy as putting an air fitting on the end, something like this:



Simply open the gas can and give 'er a good 10-15 seconds of air, depending on how much fuel is in the tank.

As far as vent lines and routings go where the fuel cap is follow that back to the tank. Usually there is one large line for fuel and another smaller line running in conjunction for a vent line.

If this doesn't help I would pull the air filter, and try to crank it while you have a buddy looking at the fuel bowl in the carb. If you can get fuel to the carb you know it's not a fuel issue, and you now know it is probably a spark issue.

You need fuel and spark:

I'd take the gas tank and lines completely out of the equation.

Get a 2 gallon portable gas tank. Run a soft line from the fuel pump inlet into the portable tank.
This is a good option too, I was just too cheap to spend an extra ~$40 for a tank, primer bulb, fittings, lines, etc

As others have said you are doing pretty well for as little experience as you say you have.
 

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Discussion Starter #14
I'd take the gas tank and lines completely out of the equation.

Get a 2 gallon portable gas tank. Run a soft line from the fuel pump inlet into the portable tank.

Do you have a clear fuel filter at the carb, so you can see that gas is flowing?
I did all of that. The results were...inconclusive. Which resulted in me changing the fuel pump. $30 for the pump and 30 minutes to change it out.

I am definitely getting fuel where it needs to go. Now whether there might be something in the fuel tank getting sucked up? Not sure. However, I am pretty sure my sending unit in the tank is shot now also. The fuel gauge is pegged past the full mark. And doesn't move.

As to why I haven't checked the spark. My mind just doesn't work that way. I did as much research as I could on the symptoms. There is a whole laundry list of possible causes. So, I just picked what I thought would be the most likely culprit and eliminated that cause.

Now, it's time to move onto the next item on the list. Which apparently the ignition is as good a place to start as any.

Is there any particular reason why I shouldn't just replace the MSD distributor with the same? It was working, and working well. If it is the problem, then it is just as easy to replace the unit with the same (new) unit. Might as well replace the coil as well.

Of course, it might just be a bad ground somewhere. I truly HATE chasing ghost ground problems.
 

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Discussion Starter #15 (Edited)
It's as easy as putting an air fitting on the end, something like this:



Simply open the gas can and give 'er a good 10-15 seconds of air, depending on how much fuel is in the tank.

As far as vent lines and routings go where the fuel cap is follow that back to the tank. Usually there is one large line for fuel and another smaller line running in conjunction for a vent line.

If this doesn't help I would pull the air filter, and try to crank it while you have a buddy looking at the fuel bowl in the carb. If you can get fuel to the carb you know it's not a fuel issue, and you now know it is probably a spark issue.



This is a good option too, I was just too cheap to spend an extra ~$40 for a tank, primer bulb, fittings, lines, etc

As others have said you are doing pretty well for as little experience as you say you have.
Lol. Trust me. I have had to call my father in law before to help me get a push lawn mower running (he passed away in October, or I would have him help me with this. That man had a way with engines.). Just because I understand how it is supposed to work doesn't mean I know how to fix it when it doesn't.

I can tell you how a nuclear reactor works also, but you better hope I'm not the only guy to fix it when something goes wrong.
 

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I did all of that. The results were...inconclusive. Which resulted in me changing the fuel pump. $30 for the pump and 30 minutes to change it out.

I am definitely getting fuel where it needs to go. Now whether there might be something in the fuel tank getting sucked up? Not sure. However, I am pretty sure my sending unit in the tank is shot now also. The fuel gauge is pegged past the full mark. And doesn't move.

As to why I haven't checked the spark. My mind just doesn't work that way. I did as much research as I could on the symptoms. There is a whole laundry list of possible causes. So, I just picked what I thought would be the most likely culprit and eliminated that cause.

Now, it's time to move onto the next item on the list. Which apparently the ignition is as good a place to start as any.

Is there any particular reason why I shouldn't just replace the MSD distributor with the same? It was working, and working well. If it is the problem, then it is just as easy to replace the unit with the same (new) unit. Might as well replace the coil as well.

Of course, it might just be a bad ground somewhere. I truly HATE chasing ghost ground problems.
you are doing great... and you are interested.. so, keep going.. here is the thing... replacing parts is fine, but it is inefficient cost wise and no guarantee that you will fix the problem and, sometimes, you introduce new complexity into the system. But, hey, have at it!

I fixed my friends truck last weekend with some similar symptoms... what we determined (by eliminating variables) was that when we went to start the truck the voltage took a dive to 7 volts from the normal 12. Lots of variables (like fuel) eliminated when we found that. In this case, his truck is old and lots of things are almost 30... so we decided 'starter' and while at vatozone we got new positive and negative cables... problem solved.
 

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Gave up on the Jeepforum thread eh? Yeah we're a bunch of tards over there. I figured you already went through the ignition system, but I forgot, you're not a mechanic. Yeah for sure could be a bad ignition coil, or pickup in the distributor. Just because it won't start up the next morning after cooling off doesn't mean anything. Change the coil first, because it's for sure easier and I think cheaper too. If that doesn't fix it, then you are going inside the distributor to replace the pickup.

EDIT: Easily could be a janky MSD 6AL as well. MSD parts of today are not what they were back in the day.
 

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coil or ignition module going bad, they can drop out when they heat up and nothing will get them going until they cool off again.
my guess also.

bad ignition module will crap out when warm, run flawless after sitting a while.... for about a dozen or so times, then it just stays dead...

next time it craps out, pull a plug, try grounding it out, and see if it sparks.

If it fails to spark, then your problem is in the ignition... bad coil, bad module, bad something.... (cap, rotor, wires, whatever_
If it does spark, then pull the air cleaner off, look down the carb, and see if it has fuel when you activate the throttle.
If it has fuel (and spark) then do a compression check on all 8 cylinders.
 

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Discussion Starter #19
Gave up on the Jeepforum thread eh? Yeah we're a bunch of tards over there. I figured you already went through the ignition system, but I forgot, you're not a mechanic. Yeah for sure could be a bad ignition coil, or pickup in the distributor. Just because it won't start up the next morning after cooling off doesn't mean anything. Change the coil first, because it's for sure easier and I think cheaper too. If that doesn't fix it, then you are going inside the distributor to replace the pickup.

EDIT: Easily could be a janky MSD 6AL as well. MSD parts of today are not what they were back in the day.
Nah Tipped. I just wanted another viewpoint. I'm gonna just take it to a mechanic. The MSD 6AL is the 6420 which you can't get any more (new). Not sure if it's from "back in the day" or not. But definitely not giving up on jeepforum.com.
 

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Discussion Starter #20
Well, the adventure continues. I loaded the old yellow dog up and drug her to my mechanic. Been using him for years. He got her into the bay today and called me up about 3 hours later. "Carb not pumping gas. Where did you get this thing from?" So he's going to swap the carb. Not sure if I believe that this is the problem. If it is, then I'm a crap wannabe mechanic. :homer:
 
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