78 L20b #1,#2 cylinder dead at idle

[Sar_moby]

Well I need some ideas of what could cause the following problem:

 

 

95k mi on vehicle

I know there is a head gasket leak- water seeps out the back of the head when cold and the thermostat is closed.( next to the good running cylinders)

Cylinder 1 and 2 seem to not be firing( pull plug wire at idle and no difference) especially noticeable when cold. With the choke on the higher idle and rich mixture make it run okay. When fast idle cam drops out, it wants to die unless the idle mixture is richened up.

Off idle the motor shudders a bit but revs great all the way up. On the road( hot) the motor revs and pulls well.

 

things I checked:

spark on both cylinders- nice arc from plug wires, compression hot( 120,125,128,125), rebuilt carb, adjusted valves( intake on cylinder 1 was too tight, seafoamed the engine- lots of smoke= carbon build-up

Timing set to factory specs

new fuel filter

new ignition componets

 

Theories:

Bad intake/exhaust manifold gasket causing a leak at idle.

Burned intake valve

bad head gasket between cylinders 1 and 2 ( wouldn't the compression test show this?)

Bad (new) sparkplugs( NGK)- they did not look as colored as the rear two but were clean.

blocked intake manifold?

 

things to try:

I will try pulling #1 wire when cold and see if the high idle and rich mixture make a difference.

swap spark plugs?

 

Anyone with other ideas, thanks for the help.

 

Scott

[Cruzn620]

I would go with intake manifold gasket leak. I have this on my 620 and it will not run right or hold an idle untill you are spinning enough RPM's to overcome your loss of vacuum. get the motor running and take carb cleaner and spray around your manifold, if your motor revs up when you spray, you have a leak...you can also trace your leak this way. if you have a bad intake valve, this should have shown up on your compression test. You said your head gasket was already shot, so you need to get that fixed before you get water into your bottom end with will trash would main bearings. so if you take the head off to replace the gasket, you can fix all your other problems, check that intake valve, and replace your manifold gasket. I also highly doubt that new NGK spark plugs could be "bad" i have used NGK only in my bikes and cars and have never had a "bad" one before. Good luck with your build!!!

[Guest DatsuNoob]

If you have dead cylinders, it usually ends up being a bad head or electrical problem in the ignition system. Have you done a compression test yet? Harbor Freight tools sells 'em cheap. I would take the head completely off(since you have to do a head gasket anyway) inspect the valve train, as well as checking for warpage. Break out the four foot level(a straight one)

and check for even flushness all the way around. My level stays accurate to

.005" so this is a decent method. If it's bad, look for a good used closed chamber head, and Bob's your uncle.

[Guest DatsuNoob]

Oh I noticed you were using NGK plugs, funny you should mention. Hainz came over one day when I thought my timing was 180 out. Turns out my assumption of having everything set up right was correct. We checked everything, then when he was scratching his head on what to do next we pulled the spark plugs(NGK V-powers) and they were fouled. Brand new, but fouled. He swapped in some USED el cheapo autolite plats and it ran like a top. Point of the story, more expensive isn't always better.

[Sar_moby]

Thanks for the quick replies.

 

While the compression test was solid, the intake leak seems most likely. Both of those cylinders are siamesed( I think) and a bad leak would kill both of them.

 

Any other possiblities ?

 

I have the head gasket but it will be awhile( if ever) that I tear this down.

I have two cars ahead of it( one with a timing belt and ironically,a second with a head gasket as well= practise?).

wife wants the car to "go away" but I keep trying to make it a daily driver.

Can't let an old car die without a fight.

 

Thanks- Scott

[banzai510(hainz)]

tighten all the intake and carb bolts.Relative, it is a Jap motor with aluminum. Dont pull out the threads

 

adjust the valve lash so you know it closes. I just make sure the rocker arm wiggles loose abit and call it good (for now)

 

If you removed the plug wires at one time or someone else did make sure the fire order is Counter clock wise 1 3 4 2 . I assume it good sinceyou said it run all the way up the rpm fine

 

When cking the valve lash I assume the lash pad is in the retainer. Sometimes they can fallout.

Ck the bottom of the disrtibutor cap to make sure the contacks are still there. You said that was New also. So cant be that

 

If the rig idles with 2 cylinders I assume the intake is tight enough already cause it would DIE if there was a leak. spray starter fluid around some areas and see if it runs better for a second

 

Like noob said replace the plugs or swap them around

 

plugged idel jet?????????

The L20s had a 12volt wire to a idle cutoff selinoid. This is when motor shuts off to stop gas from going in the carb .Keep it from run on(dieseling)

 

 

YOu say it runs better with the choke?????? doing that makes it suck gas out of the main fuel jet faster.

 

later L20s had alot of pullution stuff on there so Datzenmike or other would know more on these. EGR valve ect........???????

[hang_510]

distributor? points?

how does it look under the cap?

 

i had a bad dizzy(worn shaft=wobble) that would function at high RPM but barely idle

[banzai510(hainz)]

what hang 510 said,

 

I had points on my 521 and it was just missing once the rpms got up

but idel was fine so I dont think its a worn distributor bushing

replace with another dist and worked ok.

 

just wiggle back and worth from side to side. if alot it can open the points when you dont want it open(fires)

[Sar_moby]

Okay, thanks for the thoughts. It does not have points and I did check the mag pick-up clearance( did not wobble the shaft though). I would think a bit of wobble would chew up the mag pick-up pretty fast if it were loose. I will wobble it and try spraying carb cleaner around the intake manifold.

 

I got the link to Hainz video- will look at that as well.

 

Let you know what I find.

Scott

[banzai510(hainz)]

if EI distributor(elelt ignition) I would worry about the wiggle. rule that one out.

as for the valve lash just make sure the lobe is on the back side between 10-2 oclock position and adjust the lash or see if its loose(meaning th valve is down all the way making a good seal)

 

Im thinking its Fuel related. cause you said you had spark to 1&2 clylinders.

So make sure the fire order.

 

did this just do this all of the sudden or you changed something? If you changed the dist cap then I assume you put the plug wires on wrong?

[Sar_moby]

I think this problem precedes my ownership( car had a stuck float when I got it). It runs solid at higher RPM so a bad plug wire would misfire at high rpm. I did a hot valve adjustment and got the factory setting on intake and exhaust though I did find #1 intake tight. Rest of valvetrain looks good.

I did not yet check the intake manifold but that seems most likely at this point.

Will advise when I test this - tonight.

 

Great video Hainz- thanks

Scott

[Sar_moby]

Well, I sprayed carb cleaner around the #1,#2 intake manifold from the top and sides and did not notice any change. It is very difficult to get to the bottom part of the intake manifold on a smog equipped l20B so it could be leaking from the bottom side, cannot tell.

 

Another thing I noticed but have not tried yet is that the vacuum connections tee goes into that leg of the intake manifold. I will try pluggin both vacuum lines( no vacuum advance) and see if there are any changes. All that would need to happen is bleed enough air into that leg of the manifold to drop the mixture lean and those 2 cylinders would not fire. I will check it and report.

 

The BPT valve is disconnected now as is the EGR to make sure they are not contributing to the problem= no change.

 

Anything else to check?

 

Thanks

Scott

[Cruzn620]

put a straw on your can of carb cleaner and just shoot it as close as you cal to the bottom of that manifold. if its not changing rpms...you have eliminated 1 cause already. good luck with it!

[banzai510(hainz)]

I got a 521 running just buy adjusting the misture screw!!!!!!!!!

[RacnJsn95]

Do a leak down test.

[Sar_moby]

that is a good point:

 

When I did the compression test, I let it crank 8 revs and then made sure it held the pressure for at least 30 seconds, no leaks noted.

 

Thanks

Scott

[bluemeanie]

that works, but i've noticed that some of the newer compression testers have a check valve that you have to push to release the pressure. Make sure you dont have the kind with the valve.

[Sar_moby]

I think mine has a relief valve but not a check vavle, I can try removing it under pressure to confirm if it leaks down when unscrewed from the cylinder hole.

 

Thanks

[datzenmike]

The BPT valve is disconnected now as is the EGR to make sure they are not contributing to the problem= no change.

 

Anything else to check?

 

Thanks

Scott

 

On the '78 the EGR valve will be closed at idle and when the engine is cold. On a warm engine above idle the EGR valve opens in direct relation to exhaust back pressure. Simple, however it is possible that the EGR valve isn't closing when it's supposed to, (carbon build up) causing a slight vacuum leak at idle. (this would affect ALL cylinders though)

 

If you disconnect the rubber hose and undo the two 12 mm bolts you can remove it and clean the valve with a wire brush. You'll also see how it works and if it is closing properly.

 

There is a bung on the back runner that the vacuum line for the power brakes connects to. If it's damaged or the hose is cracked there'll be a vacuum leak.

 

Did you replace the distributor cap and rotor?

[Sar_moby]

Update-

Turned the idle mixture out two turns until the enging idled pretty smoothly and now at tip in the engine stumbles. If I lean the idle mixture, the stumble goes away but I loose #1 and #2 when cold with no choke.

After making the mjxture adjustment I pulled the #1 spark plug and did not notice any difference in the idle of the engine.

Can this be "normal" on an L20b? Is it possible that the rear two cylinders are running that much leaner than the fron two? I did disconnect two vacuum lines( plugged) and they made no difference.

On the EGR, I removed it and the manifold adapter 2 months ago and cleaned out the carbon build-up. I have the vacuum to that and the BPT plugged right now so no EGR at all so I can diagnose the poor idle.

I have also tried to spray carb cleaner around the intake with no change to the idle ( may not be able to get to the bottom of the intake manifold).

After adjusting the carb, took it for a drive and it pulls well( all cylinders firing but maybe a little rich). Carb is a =DCH 340 with a 103 primary jet.

 

Now, I can live with a rich idle if I can get rid of the bog at tip in. The accelerator pump has two positions for the plunger and three positions on the lever arm.

Question: To reduce the shot volume at tip in ( too rich condition especially on #3 and #4) I would assume( dangerous) that I should move the rod toward the pivot (reduce throw). Is that correct?

What else can adjust the off-idle mixture?

 

Thanks all

 

Scott

[banzai510(hainz)]

i just adjust the mixture in/out intill its smooth.

 

that intake is prettymuch equel runns so I dont know why the first 2 cyls are what they are. besides the manifold on that end has something wrong with it.

 

I am of no help anymore,sorry. I got no more awnsers.

[hang_510]

how are the return springs?

maybe the butterfly doesnt close all the way during idle?

[Sar_moby]

I think the return springs are okay( had not thought about it). I can adjust the idle speed at the screw without problems.

Good thought though, thanks

 

Scott

[datzenmike]

 

Another thing I noticed but have not tried yet is that the vacuum connections tee goes into that leg of the intake manifold. I will try pluggin both vacuum lines( no vacuum advance) and see if there are any changes. All that would need to happen is bleed enough air into that leg of the manifold to drop the mixture lean and those 2 cylinders would not fire. I will check it and report.

 

Thanks

Scott

 

Scott there is no vacuum connections TEE going to the 1&2 intake runner. There is a plugged hole there and it is not used. There IS a hole in the 3&4 runner for vacuum for the power brakes. Check it out.

 

There are two ported vacuum outlets on the valve cover side of the stock carb. The one to the front should have a hose going to the vacuum advance of the distributor and must be hooked up to give good throttle response just off idle. Make sure it is connected and not leaking. The second port is for the EGR and should be plugged at the carb to eliminate leaky hoses. Once your problem is fixed it can be connected back up if you wish.

[Sar_moby]

DatzenMike-

 

78 smog vehicle uses a two port threaded fitting on the #1,#2 intake manifold leg where one manifold vacuum source goes to control the air injection system (fender mounted) and the other ( I believe is the anti-backfire valve?) also located on the fender. I plugged one of them and you get that motorboat sound from the air injection system. hooked them both back up= no change.

 

Now I am looking at the accelrator pump to see if the motor needs more fuel on tip in or less. I am not clear on the best settings and must change the plunger rod setting and the pump lever to change the magnitude of the pump shot.( is there any other way?)

 

Motor starts great with the choke on, then the rpm drops when the choke is out of the way (set choke to colder setting?) and with the rich setting on the idle mixture, as it warms up it appears to run on more than two cylinders. Except for the tip-in the motor pulls quite well.

The remaining problem is the bog on tip-in.

I have a new accelerator pump in the carb but when looking down the primary it seems to only squirt a fairly small, steady stream of fuel( as compared to my toyota 22R- or my imagination).

 

I appreciate all the suggestions and help.

 

Almost a daily driver

 

Scott