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JeepJon15 12-12-2011 06:38 AM

High idle then dies 88 yj 4.2
 
Hello all. This weekend i decided to swap out my non working ignition module with the HEI gm module. The switch out was somewhat successful, i now get a consistant spark and it starts up pretty strong.


When it first fired up my rpms were really high, maybe 1500. Eventually it smoothed out and actually died. I spent some time adjusting the timing (a bit high at 12 degrees) and fuel/air mixture screws (it was already nuttered). After 10 minutes of work i got it to idle pretty smooth at about 800rpms. It was still a little weak idling in gear, but it still has the original carb, so its not suprising.


This morning, it did the same thing as last night before makeing the adjustments. It idled around 1300 for about a minute or so, maybe a bit longer, and then died. It started right back up 3 or four times, but kept doing the same thing.

EDIT: I thought i should add... when its dying now its not like the key is turned off like it was before replacing the ignition module. Now i can tell the rpms are dropping and can feather the gas and keep it from dying.

I'm thinking clogged idle tubes and timing too advanced? I'm not pro at setting the fuel/air mixture screws, i kind of just wing it so maybe that too. My question is why was it running well last night and now acting screwy? Any advice would be awesome. Thanks!:2thumbsup:

Old4X 12-12-2011 01:17 PM

When you do this mod, it is important to use heat sink compound (not dielectric grease), and firmly attach the module to a well grounded heatsink.

Also, you must twist the 2 pickup wires all the way from the distributor to the module. Good, tight connections are also a must on all wiring involved.

Is your dizzy set up to pre-smog as far as mechanical advance?

Is your vac advance on manifold vacuum (should be)? And is it moving freely?

Old4X 12-12-2011 01:19 PM

Also, sounds like you have one or more vacuum leaks. Check closely all vac sources (including carb base, vac lines, egr valve, intake manifold gasket area).

JeepJon15 12-12-2011 01:33 PM

Hey thanks for the response. I used heat sink compound and it should be grounded just fine. I nuttered it last summer, the two wires are already twisted... There may be an inch or so where it hooks up to the new module that they arent twisted... but my spark is strong and consistent at start.

-My distributor hasn't been messed with really, should be stock. I've replaced my cap and button somewhat recently, but with basically a direct replacement. EDIT: I did plug the dizzy and reset the timing, guessing thats what you were asking. Its at 10-12 btdc, i know its a bit high, but with the way its been running that seemed to work best.

-I have the vacuum running to the manifold as instructed in the Nutter Bypass how to page. What do you mean by is it moving freely?

I was actually out there just now checking for leaks. Two of the bolts on the manifold were pretty loose, so i snugged them all up. I cant find any other obvious air leaks.

Thanks for your advice. Let me know what you think.

JeepJon15 12-12-2011 03:18 PM

Thought i'd leave a little update. I've been in the driveway messing around with the jeep. I reset the timing back to 8 degrees just to try to get on baseling. I messed with the carb linkage just moving it around to make sure its not hung up.

I did redo the two screws on the base of the carb toward the front of the jeep, i believe these are the mixture screws. I brought them out 4 turns to start, i saw someone give that advice, and slowly tightened them from there (not a whole lot of tightening needed it seemed). I also have the ?idle screw? turned in quite far. The screw i'm talking about is the closest one to the fender on the linkage.

After all this seemingly aimless tinkering... the jeep is idleing at 8-900 rpms as i type this, and has been for 10 minutes. Basically the same thing i got it to do last night. Is this because i did something good? Or because it just takes me tinkering that long for it to heat up and this is causing it to run better?

I got it to run like this last night and test drove it, it drove okay, and shut it off and this morning HIGH rpm for a minute, then dead. Should i expect it to revert back to this? What else should i be doing??

Thanks! :o

EDIT: Still running after at least 15 minutes. Going to shut it off and let it cool down and see if it will still run.

JeepJon15 12-12-2011 04:02 PM

Any thoughts? Jeep has been down for a couple weeks now and its my only car! Would really like to tackle this this week if possible. If the idle tubes were clogged would it run for an hour tonight and be finicky the next morning? I've cleaned them once around june or july, it may be time again... but i dont know if this is the problem.

Old4X 12-12-2011 07:19 PM

You need to adjust the choke coil and choke-fast idle speed.

On a warm engine, set the high idle cam on the second notch. (this is the swinging cam on the throttle shaft closest to the carb body). Adjust the idle speed with the inner adjusting screw to 1600 rpms +/- 100 rpms.

Now, you have to wait till the engine is stone cold to set the choke coil. The carb rebuild kits have the spec to get close, but I usually start withe the choke closing the choke plate to about 3/16" from full closed. (you have to operate the throttle linkage once to engage the choke). The coil is adjusted by loosening the 3 screws holding the cover, and turning the choke cap the desired direction to open or close the choke as needed.

The engine should start easily when cold, and have a fast idle. As soon as it stabilizes, pump the gas pedal once to let the choke pull-off drop the idle to a reasonable level (around 1,100 to 1,200 usually unless it is below 40 degrees).

Now once the engine gets to operating temp, set the idle speed to about 750 rpms.

Next, try fine tuning the idle screws. Turn each in till they just bottom, then back out 1.5 turns each. Using a vacuum gauge, slowly adjust each screw (1/4 turn at a time) for maximum vacuum reading on the gauge. Make sure the screws are within 1/2 (or less) turns from each other.

You may have to re-adjust curb idle again to 750, and the fast idle (2nd notch on cam) again.

Timing should be 8 to 9 degrees BTDC (vac line plugged going to dizzy). If you have to readjust timing, you will probably have to tweak the idle speeds again, timing and mixture each affect idle speed.

You can check the vacuum advance setting while you are under the hood. With engine off, take a 1/8 inch hex wrench and turn the screw in the snout of the vac can in till it bottoms, make sure you count the revolutions. Should be 7 to 8 full turns, if not, set to 7 turns out from bottom (write this down so you don't forget).

Hook everything back up and go for a ride and see how she does.

JeepJon15 12-12-2011 08:22 PM

Awesome, thanks so much Old4x, this was the kind of reply i was hoping for. I've seen much of this information in separate places but it seems putting it all together was beyond me.

I'm going to work on it before work tomorrow morning and see how far i can get, ill have till around noon.

I went out and got some carb cleaner with the intention of cleaning out the idle tubes (the jeep made it to the parts store!) but for now i think ill just give the carb a good spray untill i have done everything you just suggested.

Once again, thank you for the post. It was perfect because everything i know about cars i've learned from my jeep, and shes not a very good teacher. So detailed instructions keep me from getting overwhelmed and saying screw it.

Anyway, ill report back tomorrow!! I HAVE DIRECTION

Old4X 12-12-2011 08:32 PM

Carb adjustments aren't cast in stone. Especially with the choke coil setting. It isn't unusual for me to tweak the choke coil setting 3 or 4 days in a row till I hit the sweet spot for that particular engine.
Same with curb idle, timing, etc.

What I outlined above should work, but do not be afraid to adjust up or down a little on stuff (and write down what you did so you can undo if necessary).

Good luck and keep us posted.

oldtime_ironman 12-13-2011 04:07 AM

Quote:

Originally Posted by Old4X (Post 12666000)
Carb adjustments aren't cast in stone. Especially with the choke coil setting. It isn't unusual for me to tweak the choke coil setting 3 or 4 days in a row till I hit the sweet spot for that particular engine.
Same with curb idle, timing, etc.

What I outlined above should work, but do not be afraid to adjust up or down a little on stuff (and write down what you did so you can undo if necessary).

Good luck and keep us posted.

Completely offtopic, but I just wanted to say that it made my day to find somebody else who knows about carbs and timing. I was starting to think that I was the last one on earth... (I used to do GMC 4-barrels for performance)
.

JeepJon15 12-13-2011 04:30 AM

Haha, well let me tell you, it made my day too. It gave me some hope that i can learn! I'm going out to work on it in an hour or so, wish me luck. I'll post how it goes.

By the way, Old4x. Just noticed you have a 90 cj7. Does that mean lots of CJ parts on your yj frame? Just curious.

Also Old4x: I dont have a vacuum guage. Can i get close to the proper idle screw setting by ear? Getting started a little slower than i thought this morning, but its still before 8am here.

JeepJon15 12-13-2011 07:30 AM

Okay just went out and warmed her up. She started up pretty easy this morning and idled at about 750 rpms surprisingly... That lasted about 45 seconds and she died. Anyway i feathered the gas till the engine got somewhat stable and eventually would stay on. Got up to operating temp and i set the idle to 1600rpms. Now waiting on it to cool. So far so good...

Another question though. This is about the next step, the choke plate. You say you usually start with the plate 3/16" from closed. Does this mean that number is just a starting point for the plate and i will probably have to tweak it? Or is that a good place to keep it? If i need to tweak it, is it simply the more open it is, the less choke and lower idle? I'm sure there is more to it than that, but as far as this procedure is concerned... Thanks!

oldtime_ironman 12-13-2011 07:52 AM

Quote:

Originally Posted by JeepJon15 (Post 12667685)

Another question though. This is about the next step, the choke plate. You say you usually start with the plate 3/16" from closed. Does this mean that number is just a starting point for the plate and i will probably have to tweak it? Or is that a good place to keep it? If i need to tweak it, is it simply the more open it is, the less choke and lower idle? I'm sure there is more to it than that, but as far as this procedure is concerned... Thanks!

The overall concept is to have a slight gap around the choke plate. 3/16 is a ballpark figure, a place to start with far as I can tell. For example, on the old Chevy's they would tell you to use a 1/8 drill bit and stick it in there, to set the plate.
Usually the idle will go UP with more choke because it has more gas. Compared to the amount of air its getting. Its kind of a balancing act - you want the choke completely open when its fully warmed up and off the choke cam. But you want it nearly closed when its dead cold and the choke is set.
.

Old4X 12-13-2011 07:59 AM

Setting the choke plate determines how long the choke stays on and provides an over-rich mixture. If the engine won't run right after kicking the idle speed down (after first start) with the choke pulloff, you need more choke (close the plate a little more).

If black smoke is pouring out and you have a deep sound to the exhaust, you need less choke.

Have you taken a can of spray carb cleaner and looked for vacuum leaks?

On not having a gauge, you can do OK without, but will get a better tune by using the gauge. A plus for these vacuum gauges is they can normally be used to check fuel pressure on a carbed motor. (another good item to check when having a stalling problem).

JeepJon15 12-13-2011 08:16 AM

Still waiting for the engine to cool. Thanks for the replys guys. I'm getting the picture that maybe my choke plate has been opening too far before the engine is ready to that much air. Is that right? Just trying to get the big picture here.

Old4x: I have checked for leaks, and it seems there may be a slight leak at the base of the carb. Not sure how bad it is, but ill have to eventually rebuild it or replace it. How soon just depends on how she runs after i finish with this process. When i nuttered it a while back i replaced all the vacuum hoses i noticed were deteriorating or leaking, so those SHOULD be good. Also thought i'd add i replaced my pcv valve last night on a whim because i overfilled my oil a month or two back and it seemed a little gummed up.

I'll check into a vacuum gauge as well. I'm sure it will come in handy while maintaining this jeep. Is a cheap $20 gauge just as good as the $60+ gauges for what ill be using it for?


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