Jeep Won't Idle - Advanced Diagnostic Assistance Requested

[Jake10]

I have a Jeep that doesn't run right. Mine is a 76 J10/258 (L6). Symptoms: Won't idle, only runs at high RPM. Starts ok and runs smoothly until full choke comes off Then it tanks unless I keep my foot in it to keep the throttle open. Seems smooth, but as soon as engine speed starts to drop it's like someone turned it off, unless I pump the gas and get the engine speed back up. Seems like it's not running on the idle circuit, only main jets, except when fully choked.

Here's what I've done so far:
- replaced the distributor (old was HEI conversion that was worn out, new is Motorcraft for '78 engine) cap, rotor, coil & ignition module. I was going to do this anyway, so it's not really a case of throwing parts at it.
- Checked timing.
- disassembled carb (rebuilt last fall) and cleared idle jet passages etc with compressed air, checked idle jets and tubes for clogging - they were clear. I have done the tube bore-out recommended in the FAQ. Did not check float level but did verify that the valve works.
- checked fuel flow both before and after fuel filter.
- disassembled the EGR valve assembly. It does not work at all, due to leaky diaphram. But the valve itself is closed and this is not recirculating any exhaust gas. I don't think it has worked since I got the engine, and I have not had it connected.
- capped all vacuum ports from the carb to make sure there were no vacuum leaks in the tubing.
- When I pulled a plug (#1, to verify TDC when replacing the dizzy) I observed that it was very clean, looked new. It is new, has less than 2000 miles on plugs & about 4000 on wires.

Where do I go from here?

Jake
76 J10 258 - the Guinea Pig

[christopher]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Jake10:
I have a Jeep that doesn't run right. Mine is a 76 J10/258 (L6). Symptoms: Won't idle, only runs at high RPM. Starts ok and runs smoothly until full choke comes off Then it tanks unless I keep my foot in it to keep the throttle open. Seems smooth, but as soon as engine speed starts to drop it's like someone turned it off, unless I pump the gas and get the engine speed back up. Seems like it's not running on the idle circuit, only main jets, except when fully choked.

Here's what I've done so far:
- replaced the distributor (old was HEI conversion that was worn out, new is Motorcraft for '78 engine) cap, rotor, coil & ignition module. I was going to do this anyway, so it's not really a case of throwing parts at it.
- Checked timing.
- disassembled carb (rebuilt last fall) and cleared idle jet passages etc with compressed air, checked idle jets and tubes for clogging - they were clear. I have done the tube bore-out recommended in the FAQ. Did not check float level but did verify that the valve works.
- checked fuel flow both before and after fuel filter.
- disassembled the EGR valve assembly. It does not work at all, due to leaky diaphram. But the valve itself is closed and this is not recirculating any exhaust gas. I don't think it has worked since I got the engine, and I have not had it connected.
- capped all vacuum ports from the carb to make sure there were no vacuum leaks in the tubing.
- When I pulled a plug (#1, to verify TDC when replacing the dizzy) I observed that it was very clean, looked new. It is new, has less than 2000 miles on plugs & about 4000 on wires.

Where do I go from here?

Jake
76 J10 258 - the Guinea Pig<HR></BLOCKQUOTE> did you adjust the base idle and curb idle? did this come on all of a sudden or gradually get worse? spray carb cleaner around the base of the carb to check for leak. if you continue to have this problen check the idle mixture screws. kicking the tires won't hurt.

[porkchop]

You said you checked the fuel flow. Did you check the fuel pump, sometimes you can have what seems to be a good flow but it isn't, so check the fuel pump. Also you need to check the float to see if it is holding any fuel. If you have no fuel in the bowl the engine will only run when you step on the gas. Had this problem and it turned out to be the float was wrong and would not allow any gas in the bowl so the only time it was getting fuel was when your foot was on the gas.

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'67/'79 Wagoneer mix
"Old Timer"
Body of a 33 year old
Heart and legs of a 21 year old.
Spirit of a 1 year old.
360,TH400,QT,D44's F&R
SOA 32X11.50's

"I regret that I have but only one paycheck to give to my Jeep."

[Bernie]

It sure sounds like a vacuum leak to me. My 232 had the same symtems and I finaly narowed it down to snugging up the intake manifold bolts and a carb spacer block gone bad. Your best bet is to spray some carb cleaner or oil every where and see if you can find a leak.

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To many Jeeps not enough money!!

[ClarkGriswald]

Did you try turning up the idle screw? Run the motor until it warms up and the choke kicks down. Then it die's correct? At this point go turn up the idle screw and observe it moving the throttle linkage open a bit more. The start it up and see if it idles. It may just be adjustments. And also the Idle mixture screws should be set correctly, you should have a vacuum gauge or a tach to set that.

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88 Grand Wagoneer
D44's front\rear
Warn 20990 Lockouts
AMC 360
TF 727
NP 229 (Funky)
Custom Hacking Via S.P.A. (Standard Polish Archetecture)

[scotty]

allright,ive been there and done that your jeep has the carter 2bbl,yes? this is the worst carb ever created.well,amybe not that bad,but they are notorious for not idling.sometimes the trouble is simply clogged idle tubes,but thats prolly not your case.another thing that happens is that the throttle shafts wear out,creating air leaks, and not letting the fuel mixture be rich enough for idle. poor quality rebuilds from cheep discount parts stores( such as the 'Zone) alot of times have this problem when you get them. when you rebuild it,you dont take care of the problem unless you comepletely "blueprint" it,much like rebuilding an engine. i have had about 6 of them from the zone.they last 3-6 months,i take them back,and they give me another year warranty.

id yank the egr valve,even if it looks fine.it may be creating a vaccum leak. the one time that my no idle problem was not carter carb related,the egr vlave looked fine,but was just creating a big,huge,vaccum leak.put on a block off plate cranked it up,ad she idled just fine. the other common prob is vaccum leaks,usually around the intake,but check all the lines,too.as bernie said,use carb cleaner to find the leaks. spray the carb baseplate,around the throttle shafts,and all along the intake.if it idles up when you spray,youve found a leak.snug the bolts,keep checking,you may need to replace the intake gasket,carb gaskets,or have the throttleshafts rebushed.id make a good egr block off plate first and go from there with the carb cleaner checking for leaks.id bet you a shiny new nickel that you problem is one of these-egr,intake leaks,or leaky throttle shafts.

i finally got sick of messing with it and swapped on a motor craft 2bbl,and so far im very,very happy with it.it runs better now than it ever has. alot of the 258 cj guys in the local club run motorcrafts,and they all seem to run well-always idle,dont cough or act funky on hills,so i finally broke down and did it,and im defiantely not sorry...

anyway,good luck,hope this helps,let us know what it turns out to be when you figure it out...

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scott
85 grand wagoneer
258 with motorcraft 2bbl/904/twin stick dana 300/dana 44/welded amc 20
38x15.5 gumbo mudders
snorkel/dual batteries/onboard air/"custom" convertable
3 inch body lift/mostly stock suspension/"modified" fender openings
custom front/rear bumpers and brushgaurd

possible small block chevy "test" swap in near future

[This message has been edited by scotty (edited September 25, 2000).]

[Jake10]

Hmmm, sounds like advice worth following. Yes, I pulled the EGR, yes it leaks "just a mite," yes I can fabricate a block-off plate. Yes my BBD has about 4000 on the rebuild and it's showing some shaft-wiggle.

What model Motorcraft carb did you say fits?

[scotty]

im not sure which one im using- a friend gave it to me,it came off a late 70-something ford fairmont.i bought an adapter plate form a little parts store that stocks them specifically for jeep guys.its a Mr. gasket adapter- i cant remember the part # off the top of my head. do you have an auto or manual tranny? if youve got a manual,all you need to do is make a new throttle cable bracket that pulls straight back on the carb linkage. i have a torqueflight auto that needed to retain the factory linkage because of the throttle pressure linkage,so i just bolted a lever onto the throttle arm on the carb so that the stock linkage could pull it down.

the other thing to look at is the gasket that comes with the adapter.some motorcraft carbs have passages on the bottom that will be uncovered by the gasket that comes with the adapter.this will create a BIG vaccum leak,so i made my own top gasket out of some gasket material that i had(bought it in a roll a long time ago).

some have a port for the pcv vlave,some dont. older fords did use a spacer that had a pcv port on the back,or you can get tricky with attaching it to some other manifold vaccum source if you cant find a carb thats got a place for it. the one im using does have a pcv vlave port on the back.

i dont think its jetted quite right yet(came off a 302),but the most fustrating thing for me so far is how to attach it to my snorkel. the carb neck is 5 1/8 and any stock air cleaner that fits the carb does not physically fit between it and the brake booster. K&N makes a trick aluminum thing with a 4 inch outlet,and even has the logo on the top.it would be perfect,but the cost is about $135.ahhh,ohhh well,ill figure it out,let me know if youve any other motorcraft swap ques...



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scott
85 grand wagoneer
258 with motorcraft 2bbl/904/twin stick dana 300/dana 44/welded amc 20
38x15.5 gumbo mudders
snorkel/dual batteries/onboard air/"custom" convertable
3 inch body lift/mostly stock suspension/"modified" fender openings
custom front/rear bumpers and brushgaurd

possible small block chevy "test" swap in near future

[Jake10]

You got me started. I ran some web searches using Google and came up with a wealth of material on swapping in a Motorcraft 2100 or 2150. Like you say, you need an adapter (Mr Gasket) for an old Rochester 1bbl for a Chvy 6, and the carb off an 80 Econoline or F150 with a 302 (they put a 1 bbl on the 300 ci 6).

I'm psyched to get to the junk yard and get one to rebuild so I can get this J10 back on the road.

For the record, it's a 76 J10, T18a (granny gear), D20 xfer case with 3.54 D44s front & rear. The 78 258 that I have in it is at least the third engine that's been in it, I got it for $550 with a barely running 258 that was obviously not the original - it was painted orange and marked as a 78 engine too. Probably a Pep Boys rebuild. PO of the engine (Brad Feick) put a Crower Bja Beast in it, but I've never gotten it running well enough to know if it's any good.

[Jake10]

Update.

Tore down the old carb. Found lots of waxy crud in the bottom of the bowls, but otherwise it was fine.

Put all back together. Still didn't run. Got desperate & took a hammer to the dizzy. Well, ok, I tapped it until I had dialed in about 20 degrees more advance. Fired it up. Muuuuuuuch better. Ran. Warmed up, got it to idle. Timed it. Idles nice - for a 258.
One of these days the Motorcraft carb goes in. 'till then the old Carter will do. The Motorcraft distributor with the Ford TFI coil and stock module for the dizzy makes this think run real nice. The dizzy has the Ford 300 adapter, cap and rotor, which has much more space between the posts. The proper advance curve makes a lot of difference. For the first time ever this thing has reasonable throttle response at most throttle & speed combinations.