Idle Trouble...

[Buzzbomb]

As the last part of my headgasket replacement, I went ahead and checked my head bolts today on my L20B to make sure they were all still tight. Only two bolts moved when checked, and they only moved about 1/4 turn. I checked all the head bolts on a low torque setting, then a medium, then finally at what my final torque setting was when I put the bolts in about a month ago. I used the instructions here, and in the PDF manual on the olddatsuns site. I rechecked the bolts to make sure they were tight, tightened the ones that weren't as the shop manual suggested- no more, no less.

 

After checking the bolts it started fine, idled fine at that time, drives fine. Long story short, I can't hold an idle now. It was just fine until I was giving it some gas to get up a hill around 60 MPH, and then I came to a stop, and it stalled out :confused: . I had to feather it home. It actually runs fine, it just won't idle for some reason. Almost like it has a vacuum leak again. PLugs look good with a greyish color on the ground strap, choke seems to be working alright (it's open when hot).

 

I wanted to ask if there were any other suggestions you all might have to add to my list here...

 

1)REcheck the manifold bolts. I used anti-seize on these bolts. Was I wrong to do that? Could that cause them to want to loosen up?

 

2)Check the anti-diesel solenoid..Unplug/plug- easy check.

 

3)Check EGR. Can I just unplug the hose coming from the "valve" that the EGR is hooked to, and then also plug the vacuum port on the EGR to eliminate it from the mix?

 

4)Valve adjustment...Can valves that are out of adjustment cause idle problems? I haven't adjusted the valves yet after replacing the head gasket.

 

Anything else I could try here?

[datzenmike]

Anti seize is a good idea, won't loosen them.

 

EGR is not working at idle so not a factor. However it could have deposits on it that prevent it from closing. This will most definitely affect idle. Try to flit up the valve shaft with your finger nail. It is spring loaded but do-able. Let it drop back into place. This may dislodge any carbon and help seal it. Alternately, you can unbolt and clean properly with a wire brush.

 

Check the valve lash.... might help/won't hurt.

[Buzzbomb]

It seems like a crazy coincidence for this to all of the sudden happen when I checked the tightness of the headbolts. That being said, I kinda think (or at least hope like heck) that it actually IS a coincidence. The first thing I thought when the problems started today was that maybe I did something wrong :confused: Now that I've thought a little about it, I don't see how checking the headbolts and tightening only two bolts barely 1/4 turn could cause a problem.

 

Anyway...

 

I'm glad the anti-seize wasn't a bad idea in that application...

 

I pushed up on the EGR valve and it seems free. I'll do it again though, and if it doesn't help, I'll just take it off and check the manifold bolts while I have it off. Hopefully it is something simple that will negate taking the stuff off to get to the intake bolts to check them. It's not hard, just tedious as hell :blink:

 

If that stuff doesn't work, I'll have to check the valves. I've really been hoping I could get my emissions test out of the way first, but it wouldn't pass worth a crap running like this, so I've got nothing to lose at this point :(

 

Are there any other areas other than the intake, vacuum hoses, and EGR that can cause vacuum leaks??

Edited April 8, 2009 by Buzzbomb

[datzenmike]

Actually it happened well after the head re-torque when you were driving.

 

Check throttle linkage. Reset the idle speed and mixture.

[steve g]

if your valves are adjusted too tight it could cause idle issues. my bosses 720 had horrific idle / low rpm problems and it turned out to be an EGR partially stuck open. I think Mike covered it pretty well. Is your distributor walk on you? check to see if its tight. Could it be that you adjusted the idle when the choke was slightly on?

Steve

[Buzzbomb]

Could an EGR problem show itself when the truck is actually in motion at a low RPM? Around 1500 or so? It drives just fine...It's so easy to check the valve, I'll give it a shot again.

 

All good stuff here..I'll try the easy jobs first and hopefully will get lucky. If not...argh... :lol:

[Buzzbomb]

I had a chance to mess around with my truck today...It still isn't idling correctly for some reason. I can say that it does idle better, just not smooth enough and at a low enough RPM most of the time. I say that because it's inconsistent with idle. Anyway, here's what I did...

 

Tightened up the manifold bolts to 12 lbs..Seemed to help, they turned about 3/4 turn before click. I'm hoping that's the last time after putting on the new gasket. I wanted to do this anyway due to possible gasket "creep".

 

Cleaned the EGR valve. It moves freely, didn't really need much cleaning.

 

Checked the fuel pump...It seems to be working fine.

 

Checked compression after warming it up. It's pretty much 150 across the board. Practically no variance between cylinders. Wanted to try this too after replacing the head gasket.

 

Made sure hoses are in good shape..They are.

 

Checked the anti-diesel solenoid. It clicks fine when plugged/unplugged.

 

Carb mixture screw was fine and wasn't moved, so I see no issue there. I need to get the truck E-tested, and it passed before, so should pass again at its current setting. It was set by a pro before using a sniffer, so I don't want to cause more problems.

 

Next up is to adjust the valves, I guess..Honestly, they've never been done over 100,000+ miles. I know that is pretty dumb, but I used to figure if isn't broke, why fix it? The truck has always run well.

 

I suppose it could also be the AB valve, idle compensator or some deal on the air cleaner. I guess I'll have to figure out how to test that stuff. If none of that it is it, I can't think of anything else other than a carb problem of some kind. If it was ignition, my guess is it wouldn't run right at any speed.

 

Kinda sucks :( ... It was running damn good.

Edited April 9, 2009 by Buzzbomb

[banzai510(hainz)]

anti desiel seliniod could still plug up with dirt even if its working ok. But usually when its plugged it just dies at idle right away.

 

Is there a DGV carb on here? I forgot but the ones with the cheap Carb adapter could crack and cuase a cunt hair vacuume leak.(happened to me once.

 

Sometimeres adjusting the mixture screw can fix this.

Me and jeff were working on a Datsun and it would run when you had the pedal pused down just fine but then to idle it would die.

I turn it all the way in then did half turns till it was running.

Be Honest I just got fucking LUCKY. Cause I was stumped. Plus it was the stock carb and the fuel level was fine.

[Buzzbomb]

anti desiel seliniod could still plug up with dirt even if its working ok. But usually when its plugged it just dies at idle right away.

 

Is there a DGV carb on here? I forgot but the ones with the cheap Carb adapter could crack and cuase a cunt hair vacuume leak.(happened to me once.

 

Sometimeres adjusting the mixture screw can fix this.

Me and jeff were working on a Datsun and it would run when you had the pedal pused down just fine but then to idle it would die.

I turn it all the way in then did half turns till it was running.

Be Honest I just got fucking LUCKY. Cause I was stumped. Plus it was the stock carb and the fuel level was fine.

 

It's not a DGV, it's the stock Hitachi. If I could put a Weber on it and be smog legal, I'd shoot for that. The problem is I don't have the money for the kit right now, AND when I get an E-test, they check the underhood. I've argued with those guys many times about why my truck doesn't have an air pump :rolleyes:

 

That's the strange thing, it doesn't die at idle right away. It's sort of like gasping for breath, then it finally stalls. I can have it idling at 600 or so, but it's not a smooth idle, and it finally stalls. Maybe I do have a small vacuum leak somewhere, but I just don't know where else to look! The most obvious place was the manifold, and I now have 12 pounds on all those bolts. Checked all the vac hoses, didn't even take the carb off when I did the headgasket. I just don't know where else I could be losing vacuum from. I also don't know how it can be running damn near perfect one minute, then I give it gas for a little more power up a hill, and it's idling like sh*t the next minute.

 

I'll have to bust out your video and check out the valves section again. Like I said, they've never been adjusted on my truck. I know that's pretty stupid, but :blink: ...As a last resort, I'll hit the adjusting idle mix screw. If I didn't have to get it smogged, it'd be different; I'd already be trying to adjust that sucker. Problem is I have the smog Police to contend with :mad:

[Weaver]

Read through the posts, and I don't think I read that you did this: have you checked timing? Try turning the dizzy clockwise a little bit, if there's a difference, then that's likely what's causing the rough idle.

[Buzzbomb]

Good point..I'll check the timing to be sure it hasn't moved for some reason. I didn't move the distributor pre or post head gasket, BUT stranger things have happened.

[Buzzbomb]

Quick update on this..

 

My valves were way out of whack...Nearly all intake valves were much looser than spec, and I had one exhaust valve with NO clearance, and an additional exhaust valve that was less than it should have been. SO FAR, it seems to be running GREAT! I've said this before, so I'm not getting too excited :o . However, the valves DID need attention, and I'm glad I set them. A little more "ticky ticky" than I'm used to, but then again they weren't adjusted right anyway. I used the Haynes manual method of #1 lobe up/down and adjust in sets. If this problem crops up again for some reason, I'll be able to eliminate the valve lash as a possible problem. As of this point, my truck has had what is basically a major tuneup, which in my case includes a head gasket.

 

Idle is rock solid at around 800, vacuum is pretty solid at 15 with a 1/2 variance here and there...That means NO vacuum leaks, and I'm happy about that. It's tough to check stuff like that when the engine won't idle. My throttle response is much better also.

 

Just thought I'd give a quick update..Hard to type with my fingers crossed :blink:

Edited April 20, 2009 by Buzzbomb

[datzenmike]

Thanks for the up date to let us know what worked to fix it. Always good.

[420n620]

your idle should be set at 600 rpm for a manual trans not 800 rpm's.

you also should main tain it at 600 rpm's when adjusting your idle mixture.

(you will have to go back and forth from idle speed screw to mixture screw. )

when you do get it set right, then set the idle speed screw at 625 rpm's then slowly screw in the mixture screw, when the tach show's your back at 600 rpm, this will give you the right lean that you need.

[Buzzbomb]

your idle should be set at 600 rpm for a manual trans not 800 rpm's.

you also should main tain it at 600 rpm's when adjusting your idle mixture.

(you will have to go back and forth from idle speed screw to mixture screw. )

when you do get it set right, then set the idle speed screw at 625 rpm's then slowly screw in the mixture screw, when the tach show's your back at 600 rpm, this will give you the right lean that you need.

 

I've always set it where it seems "comfortable"..The book says 600 +/- 100 rpm, so I'm not really too far off that. I have a tach/dwell set up for V8 engines, so the RPM for a 4 banger isn't dead on accurate, but I know for sure that that carb is not in the primary circuit, AND I've passed emissions previously at around 900 RPM. Running a little higher idle RPM (to where it's still in the idle circuit) helps clean up the emissions for a tail pipe test, which helps if you have to deal with it.. If I didn't have to worry about smog, I would mess with the mixture screw and set it to highest vacuum. I actually had a shop set the carb up once when I failed the e-test, and don't see any reason to change it at this point.

 

It seems to be fine (knock on wood), and other than at least checking the hot valve clearance, I'm not messing with it anymore. I need to get the smog test and get my plates at this point. Unfortunately, a smog test doesn't give you much latitude with some things that us enthusiasts can do.

Edited April 20, 2009 by Buzzbomb