Sputtering and Loss of Power - JeepForum.com
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post #1 of 19 Old 08-02-2017, 07:13 PM Thread Starter
BillytheKid66
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1987 YJ Wrangler 
 
Join Date: Feb 2016
Location: Edmond
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Sputtering and Loss of Power

Okay...I am an avid reader of this forum and get most if not all of my Jeep info here. I don't post much but I need help.

I have an 87 YJ 4.2 with a Weber 32/36 with 250K miles that is sputtering and loses power when accelerating or going up hills. I have change out the following parts:

1. Ignition Module
2. Fuel Filters (both before pump and after)
3. Fuel Pump
4. Checked compression (132 - 140 psi)
5. Added Holley fuel regulator after installing new fuel pump (set at 3.5 psi)

After all of that, I still have the same issue. Idles great, starts up with no issues but when you give it gas, it sputters and spits. If I go up a hill, I might as well get out an walk because it crawls up with no power.

What started this was one day the jeep died and wouldn't start. It turned out to be the Ignition Module and that was the first thing I replace. Since then, I have not been able to get it running smooth at all.

Any help would be greatly appreciated.

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post #2 of 19 Old 08-02-2017, 08:02 PM
mike134
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1989 YJ Wrangler 
 
Join Date: Aug 2014
Location: Cleveland
Posts: 6,034
First of all, your jeep is mad at you because you don't post enough. Post to the forum more often.

Have you done the nutter bypass and removed the outdated emissions equipment that is far past it's service life? The EGR and Pulse air system are fine IF they are still working correctly after 30 years. But It's very likely that they are not. If they are malfunctioning, they will cause driveability problems and absolutely tank your emissions results.

Second, what is the status of your tunuep? How old are the spark plugs, plug wires, distributor cap, rotor, air filter? How old is your ignition coil?

It certainly sounds like an aging ignition component issue. I wish you hadn't changed the ICM, because whenever you have trouble with the old 4.2L ignition system, it is time for the HEI from CRT Performance. Better reliability, and it changes all of the tuneup parts at once (if you get it on special with free spark plug wires). It runs around $100.

If the above doesn't help, Your carburetor could also be out of tune. You really need to keep at the carburetors. They need to be cleaned regularly and returned regularly. Maybe once per year or so. If its time for a carter rebuild kit, you might instead pay a bit more for a remanufactured motorcraft 2150 carburetor if your local government allows you to change carbs. I think they were running about $100 more than the carter rebuild kit, which includes your time of rebuilding. If they don't allow you to change carbs, you could trade up for a throttle body injection, but that is a much bigger monetary investment.
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post #3 of 19 Old 08-02-2017, 09:05 PM Thread Starter
BillytheKid66
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1987 YJ Wrangler 
 
Join Date: Feb 2016
Location: Edmond
Posts: 15
I agree....I probably need to post more.

Spark plugs, wires, distributor/rotor were all changed out about a year ago. The coil is one the previous owner changed out to an MD coil. I've had the jeep for 5 years. I only drive the jeep on the weekends so I don't put a lot of miles on it. I have not done the bypass but have recently been looking into it. The Weber carburetor was installed about 2 years ago and seems to run good. The only reason I installed the regulator was because I thought maybe there was too much fuel being pumped into the carb.

Last edited by BillytheKid66; 08-02-2017 at 10:54 PM.
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post #4 of 19 Old 08-02-2017, 10:35 PM
project_mercy
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I don't know the 4.2L or the Weber at all, but I've had to track down a fair share of carb issues. Given you think the spark component is good, I guess I'd investigate the carb next. My guess is, the carb is just gunked up and needs a good cleaning and rebuild. You'll want to double check your plugs, even if you replaced them recently, because they may be kinda fouled if the carb is running rich from a sticky float/diaphram or whatever. Make sure to set your float level after the rebuild.

If you pull the carb, if you know someone with an ultrasonic cleaner, I find that's a good way to clean all the passages out. If you know someone who reloads, a lot of time they'll have one for cleaning brass. I have a small one from harbor freight, but I mostly use it for motorcycle carbs which are a lot smaller. The HF one is also kinda mediocre, but I've used one of the nicer ones from a guy who cleans brass and it works a treat.

With your help I will resist the urge to buy a chrome grill guard for yet another day.
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post #5 of 19 Old 08-03-2017, 08:10 AM
mike134
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1989 YJ Wrangler 
 
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I'm sorry, I missed that you had the Weber. The weber is about equivalent (arguably) to the motorcraft, so upgrade wouldn't be necessary there. If it turns out to be the carb, you'll just want to rebuild the weber.

I agree with the above, check your spark plugs. you want to pull these anyway to check the conditions in the cylinders, may as well change them out since they're about a buck a piece. Use champion copper spark plugs only. No platinum or irridium.

One more question, if you only drive on the weekends, how old is your gasoline?
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post #6 of 19 Old 08-03-2017, 09:18 AM Thread Starter
BillytheKid66
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1987 YJ Wrangler 
 
Join Date: Feb 2016
Location: Edmond
Posts: 15
Mike,

I usually fill up about every 2.5-3 weeks. I say weekend driving just because its not a daily driver. These issues didn't start happening until I changed out the ICM. I may go ahead and do the HEI work, replace plugs and go from there. That would eliminate the older Motorcraft ignition components.
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post #7 of 19 Old 08-03-2017, 09:35 AM
mike134
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At some point I would definitely do the HEI. Although, you can nutter bypass first and see how it goes. You really want the malfunctioning environmental components out of there (this is usually written in with the bypass writeups). The EGR can cause a lot of problems if it isn't working properly.
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post #8 of 19 Old 08-05-2017, 12:49 PM Thread Starter
BillytheKid66
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Join Date: Feb 2016
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Posts: 15
Okay...I did the bypass today and notice some increase in power on the lower RPM's but when I got up to 2500+ it started to sputter and lose out. The idling is a little better but still has that stutter. I guess I am going to order what I need to upgrade to the HEI and replace new plugs. I would like to get rid of the old ignition system anyway and I can't really enjoy riding with it running the way it is.
Question on the spark plug gap...is it set the same or larger with the HEI?
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post #9 of 19 Old 08-05-2017, 01:35 PM
mike134
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I think the coil is a little bit hotter, so you can afford a slightly larger gap, but this should be information included with the HEI instructions.

If the instructions say you can use a larger plug gap and use the smaller stock gap instead, there's nothing wrong with that, you just don't benefit from the hotter coil that is included with the HEI.

Just a guess from memory, the HEI plug gap is around .045" with the HEI. The stock plugs are .035". The extra distance is because the coil generates higher voltage which can jump the bigger gap. This is about 30% more spark surface area to initiate the chemical reaction front, so it can be pretty significant.

Although you could still be having a carb tuning issue, I think its a good move to the HEI regardless. You're basically going to completely rule out ignition issues in one fell swoop.
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post #10 of 19 Old 08-05-2017, 02:59 PM Thread Starter
BillytheKid66
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I have been wanting to go the HEI route and this is just forcing me to do it sooner than later.

Once I get everything swapped out, I should be able to remove the ECM from under the dash and all the wires that run to it correct? I am hoping I can clean up a lot of garbage under the hood. Would there be anything else the computer controls..gauges, etc..??
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post #11 of 19 Old 08-05-2017, 03:31 PM
mike134
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Actually, if you've completed the nutter bypass, then the computer can go right now. It's not doing anything anymore. So if you want to clean up the wiring and make sure the jeep is still running before swapping to the HEI, its a good time to do so.
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post #12 of 19 Old 09-04-2017, 05:18 PM Thread Starter
BillytheKid66
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Join Date: Feb 2016
Location: Edmond
Posts: 15
....

Last edited by BillytheKid66; 09-05-2017 at 11:35 AM.
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post #13 of 19 Old 09-05-2017, 11:37 AM Thread Starter
BillytheKid66
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Quote:
Originally Posted by mike134 View Post
Actually, if you've completed the nutter bypass, then the computer can go right now. It's not doing anything anymore. So if you want to clean up the wiring and make sure the jeep is still running before swapping to the HEI, its a good time to do so.

Ok...I am digging into the HEI change out. I have been reading about the best way to wire it up. The instruction keep mentioning a #10 wire (yellow or red) from the ignition module to connect to the BAT side of the HEI. But there is no wire that size coming from it. There is a yellow #14 from the fuse box that ties to the ignition module and then goes over to the left side of the old coil. Is that the wire that needs to connect the power?

Also, trying to determine where to get the Tach wire from. It seems to be coming from the IM...which will be removed.
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post #14 of 19 Old 09-05-2017, 12:41 PM
mike134
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The tachometer was complicated because they changed the setup a few times around your year. I'm not sure how that year works. On my 1989, connecting the tach signal wire to the negative side of the coil did the trick. Try that first if the HEI allows it.


if you are talking about POWER to the coil, you can use a wire directly to the hot battery terminal. I think you should have two power wires for your coil in 1987. One ran directly to 12VDC for start up, the other one ran through a resistor to decrease current to the coil during RUN. Its possible that the previous owner ripped that out. Unlike the old fashioned old technology coils, It is OK to connect the HEI directly to 12VDC indefinitely. It was designed to handle this, and it will increase performance.
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post #15 of 19 Old 09-05-2017, 06:13 PM Thread Starter
BillytheKid66
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1987 YJ Wrangler 
 
Join Date: Feb 2016
Location: Edmond
Posts: 15
Quote:
Originally Posted by mike134 View Post
The tachometer was complicated because they changed the setup a few times around your year. I'm not sure how that year works. On my 1989, connecting the tach signal wire to the negative side of the coil did the trick. Try that first if the HEI allows it.


if you are talking about POWER to the coil, you can use a wire directly to the hot battery terminal. I think you should have two power wires for your coil in 1987. One ran directly to 12VDC for start up, the other one ran through a resistor to decrease current to the coil during RUN. Its possible that the previous owner ripped that out. Unlike the old fashioned old technology coils, It is OK to connect the HEI directly to 12VDC indefinitely. It was designed to handle this, and it will increase performance.

I wired the battery directly to the BAT side of the HEI WITH #10. The tach is the issue. I removed the old MSD coil since I didn't need it. The negative side was connected to the ignition module...which is now removed as well. I think I can run the tach wire coming from firewall that went to the IM directly to the TACH side of the HEI.
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