87 420SEL, starts and only runs a few seconds

18726 Views 41 Replies 9 Participants Last post by waybomb, Apr 10, 2010

waybomb

Discussion Starter · Jan 5, 2010 (Edited)

87 420SEL, starts and only runs a few seconds - Still need help

Have a 1987 420SEL. 140,000 odometer.

Start the car, rpms come up slow, idles fine, then races and shuts off. If restarted immediately, the process becomes shorter. If a wait of a few minutes, the process may take 45 seconds.

3/4 tank fuel, replaced the fuel filter today, still has same problem. The pumps are running, air filter ok, no wires seem to be off anywhere.

Any ideas on what to check?

Thanks in advance.

21 - 40 of 42 Posts

Teutone

· #21 · Feb 6, 2010

Should be in the forum archive.

The forum archive has a wealth of information available at your finger tips.
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Teutone

· #22 · Feb 6, 2010

newbenz2 said:
Also it runs for about 15 mins at idle then it does the rev and die... When restarted it will rev and die. The longer it sits the longer it will run... I am sooo confused...

Welcome to the forum.
Please click 'User CP' on the top toolbar and complete your profile with the car mod and location, to make it easier to answer your posts.

The forum archive has a wealth of information available at your finger tips.
The search function accepts 2 words of at least 3 letters.
For all available resources / forum features / 'how to' navigate the forum etc, please make sure to carefully read the 'Welcome to the Forum' announcement / tutorial sticky on top of the W126 page.
Cheers

ElRojo

· #23 · Feb 6, 2010

Hello again... seems this issue isn't going away easily. I'm not suggesting throwing lots of parts at the car, but the three I originally suggested still rank high with me as the potential culprits, with the FPR still looking like the prime suspect. What I'm thinking is that there's a temperature switch that sends a signal to switch to "closed loop" at 50o C or so and the circuitry responding to that signal (call it the "B" path or something) is faulty. It would appear that somehow either the fuel pumps or fuel delivery through the CIS shut down when the car goes to this "B" path, and the engine starves and dies. At one point, you stated that the car runs (and continues to run(?)) when the FPR is jumpered. Without jumpering, starting fluid (and I presume raw gas) would keep it running too, right? I'd suggest you listen for the fuel pumps after the car stalls-- if they are still running (humming), then it seems that the FPR is still doing its thing. If not, then I suggest the Jetronic control is doing something to shut down fuel supply after the "B" path signal. I'm not sure how this would happen, as I'm still a bit of a rookie when it comes to understanding the ins and outs of the CIS controls. Check these links out-- they might be of help...

Bosch Fuel Injection Systems - Bosch K-Jetronic

Auto-Solve Diagnostic Assistance

Untitled Document

Best of luck!!

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waybomb

Discussion Starter · #24 · Feb 6, 2010

1987 420sel, all stock

My son had the car towed over here.

I took one of the Fuel Pump Relays and one of the OVPs apart. Both clean.

I plugged in both open ones, attempting to watch the contacts vs dying.

The car started right up. It's been in the 20s here the last week or so, and it had not been started for a few days.

Idle is about 1100 cold, charging at 13.97 and dropping over time to about 13.75 and staying fairly steady there.

It is fine through 50c, 60c, but up around 70c, the idle jumps up to about 2200 and stays there for a while. Then, the idle starts to settle down, but the the FPR contacts open and it dies.

I did this a few times, the last couple with some ether. I can keep it running with ether, so not an ignition problem.

Then restarted, and the idle jumps around 1100-1500 all on its own. Never settles below 1100. When it jumps up to about 2200, it will do so for a while, then the FPR kicks out and car dies instantly.

Then I took the fpr out, and jumped it so it would run the pumps without the fpr. It eventually goes to 2200-2500 and does not die, nor does the rpm drop.

So, the car will continue to run with fpr jumpered, but the idle speed is very high, up to 2500 rpm.

When at 2200 rpm, disconnected the black box in the footwell, and the idle jumped up. Reconnected, dropped back down to the 2200.

Tried a different one, same indications.

Any Ideas?

I've searched all sorts of terms and must have spent 15 hours reading old posts. I can't seem to find one relating to this issue.

Help?????

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waybomb

Discussion Starter · #25 · Feb 6, 2010

ElRojo said:
I'd suggest you listen for the fuel pumps after the car stalls-- if they are still running (humming), then it seems that the FPR is still doing its thing. If not, then I suggest the Jetronic control is doing something to shut down fuel supply after the "B" path signal. I'm not sure how this would happen, as I'm still a bit of a rookie when it comes to understanding the ins and outs of the CIS controls. Check these links out-- they might be of help..

I disassembled one of the fprs (either has the same symptom). I could see the contact lever move as it dies. My son was under the car with his hands on the pump and we coordinated our findings. The lever moves and the pumps stop and the car dies.

With the FPR jumpered, it no longer dies, but the engine is racing at above 2200. It seems as if something is causing the idle to jump way up, and then kill the fuel pumps.

I'll read through the links.

Thanks alot.

Give me a few minutes to digest it and I'll try some things and report back.

THANKS!!!!!

waybomb

Discussion Starter · #26 · Feb 6, 2010

Oh, one more thing. When idling around 1100 or so (it doesn't sound like 1100, but the tach shows 1100), the idle will kinda jump up and settle back tgo 1100, sometimes quickly in succession.
Or sometime s it will jump up a few hundred rpm and settle back down.

waybomb

Discussion Starter · #27 · Feb 6, 2010

Anybody know what the auxiliary air valve looks like on this car (1987 420sel).

waybomb

Discussion Starter · #28 · Feb 6, 2010

Ok, so I went out and found the idle control unit. Thew black box mentioned earlier must be the CIS control unit.

I started it up, I pulled out the ICU and the iidle jumped up. I plugged it back in and the idle settled down.

I unplugged the CIS and the idle dropped. Plugged it back in and it went back up.

Now, whe the engine was warm and I disconnected the CIS, the idle jumped up, not down.

Any ideas?

waybomb

Discussion Starter · #29 · Feb 6, 2010

I have two OVPs, one I disassembled and one not.

With either of them, if I pull it out, the idle goes up. If I plug either back in, the idle, just as I plug it in, jumps up maybe 100 or so rpm for a split second, and then settles back down to the indicated 1100 rpm.

waybomb

Discussion Starter · #30 · Feb 6, 2010

I found what the ICV was. I took it off and inspected the inards I could see. Seemed fairly clean.

I unplugged it after I installed it. I started it up and the idle was at about 2200. I plugged the ICV back in, and it dropped back down to 1100. Does that tell anybody anything about the problem?

waybomb

Discussion Starter · #31 · Feb 6, 2010 (Edited)

So I took it back off. I spayed ether into it and it came out the other end. I then applied 12vdc to the plugs, it clacked close. I sprayed ether in with it closed. The ether did not leak out. I removed voltgae, it all came out.

I put it back on the engine and started the engine. Isle down in the 900-1000 range!

Anyway, have a dinner date and gotta go. More tomorrow.

Going to pick up a bunch of gumout and clean the heck out of it.

Back at it tomorrow...........

Aspect

· #32 · Feb 6, 2010

Where's the CIS module you unplugged located?

Benznoob26

· #33 · Feb 7, 2010

waybomb said:
I took one of the Fuel Pump Relays and one of the OVPs apart. Both clean.

I plugged in both open ones, attempting to watch the contacts vs dying.

If the OVP or pump relay is bad you won't notice a difference whether it's plugged in or not. I'm not sure how to properly test for working relays, but this clearly seems like a fuel pump relay to me.

waybomb

Discussion Starter · #34 · Feb 7, 2010

Aspect said:
Where's the CIS module you unplugged located?

In the pax footwell, on the right side, behind the kickpanel.

The idle control relay is in that same footwell, but under the carpet, above a couple of aluminum covered controls of some sort.

waybomb

Discussion Starter · #35 · Feb 7, 2010 (Edited)

Making some progress

I took the icv off and cleaned it somewhat again, put it back on, and the idle was even higher.

So I took it off again. The plunger moves freely, and if shaken, a slight rattle is heard. There is spring return pressure.

This time I propped it up so I could fill the chamber with gumout, and while the inards were submerged in gumout, I took a thin screwedriver blade and moved the plunger a bunch of times. Reinstalled it. Idle now down to a nice 650-750 when engine cold.

At about 50c or so, the idle jumps up and down abit, and once the temperature switch is made, the idle jumps back up to 1500 and climbs to about 2200.

At that point, if I unplug the OVP, or the ICV connector, or the Idle speed control box, Nothing changes with the idle.

So I am guessing I need a new ICV????

Can somebody tell me which thermo switch actually sends a signal to the ISC and how to jump it so that it always tell the enmgine that the engine is cold?

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waybomb

Discussion Starter · #36 · Feb 7, 2010 (Edited)

I think I found the switch in question - would it be B11/2? Looks like it is the one closest to the throttle unit, sort of rear and left of the cold start injector?

On a cold engine, is that switch supposed to be closed or open or go to or open from ground?

When above 50c or so, does it close, open or go to ground or disconnect from ground?

The schematic shows 4 pole, but I am not smart enough to tell from the schematic how to test it.

EDIT-
I found the answer on another sight:

B11/2 CTS

Temp C -- K Ohms

20C -2.5K
30c - 1.7k
40c - 1.18k
50c - .84k
60c - .60k
70c - .435k
80c - .325k

My B11/2 drops in ohms similar to these indicated, though the readings a a tenth or two higher, based on dash gage. I don't think the dash gage is perfect.
In any event, as the engine warms up, the resistance drops.

If I unplug the switch, for infinite resistance, idle is high. Pluged one wire back in, and the idle dropped a bit. Plugged in the other, no change.

I am looking locally for a different Idle control valve and a different idle valve control electronic box.

I did open mine up. The piggy-back board has a sticky substance on it, maybe a corrosion inhibitor? It does not smell burned. I plugged it in without it's protective case and wiggled it around a bunch with no change in idle.

I disconnected the red/green wire from B11/2, idle drops a bit. {Plug it back in and it's back to where it was. When I disconnect the other wire, no change.

Anybody?

And another edit - I was checking resistance between the two poles. That was wrong; suposed to check from each pole to ground. The readings don't ibe with what's expected above. Trying to find a local switch.

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ElRojo

· #37 · Feb 7, 2010

Well, now it looks to me like you've got the ICV working right (after cleaning). If it's holding 650-750 when cold, it's looking like the thing works. The next thing I'd look at is the idle speed control relay (the little one in the pax footwell). Strikes me that the box has a bad circuit when the car gets warm and signals "closed loop." The relay then sends an incorrect signal to the ICV which remains open (appears like there's NO signal), and the car races. It could also be that the same signal is telling the FPR to shut down the pumps. So next on my list would be to replace the idle speed controller in the footwell.

I know you have local sources, but I have a few ICV and ICR (speed control) units in my garage, if you need 'em.

newbenz2

· #38 · Feb 7, 2010

Well everyone, we replaced the Idle control valve and the Idle control relay and still doing the same thing..... Anybody have any other Ideas? Could it be the computer itself?
Kevin

Grumpy560

· #39 · Feb 8, 2010

do as mvmiller had suggested in an earlier post and check the air plenium tubes. if you checked the air plenium tubes along the valve covers and under the intake then I suggest you re-check that area again. kind of wiggle the airtubes around very gently and see what happens. use a spray bottle of clean water to do this test. you need to spray a mist of water and not a stream around the connections and the injector holders. the problem you are having is definatly a vac leak somewhere in the system. either by way of the airtubes, injector o-rings and seals, icv tube and all of the formentioned vac lines, the rubber boot under the airflow meter or possibly the 8 rubber o-rings under the intake. look up my thread on this and you will see what we are trying to tell you here. you can change out the ICV, ICR and the ECM and have no change at all if you have a vac leak. by the way. the ECM will have nothing to do with this at all. I had this same issue a few months back, go read my entire thread titled 89 560SEL check engine light on, hard start. there are many pics in that thread that will show you more or less what these air distribution tubes do and how brittle they become after years of use. I also did a search about "high Idle" and found alot of info there so you might want to do some reading in the archives for awhile. good luck.

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newbenz2

· #40 · Feb 8, 2010

benz560sel4u2nv said:
do as mvmiller had suggested in an earlier post and check the air plenium tubes. if you checked the air plenium tubes along the valve covers and under the intake then I suggest you re-check that area again. kind of wiggle the airtubes around very gently and see what happens. use a spray bottle of clean water to do this test. you need to spray a mist of water and not a stream around the connections and the injector holders. the problem you are having is definatly a vac leak somewhere in the system. either by way of the airtubes, injector o-rings and seals, icv tube and all of the formentioned vac lines, the rubber boot under the airflow meter or possibly the 8 rubber o-rings under the intake. look up my thread on this and you will see what we are trying to tell you here. you can change out the ICV, ICR and the ECM and have no change at all if you have a vac leak. by the way. the ECM will have nothing to do with this at all. I had this same issue a few months back, go read my entire thread titled 89 560SEL check engine light on, hard start. there are many pics in that thread that will show you more or less what these air distribution tubes do and how brittle they become after years of use. I also did a search about "high Idle" and found alot of info there so you might want to do some reading in the archives for awhile. good luck.

When it has an idle of 750 when cold I sprayed carb/choke cleaner around all the tubes and by all vac connections and the rpm did not race until the car warmed up..
Kevin

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