[waybomb]

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.

 

[mvmiller]

Ignition coil?
Bad ground strap?
Crank position sensor? (green wire going to the Ignition module (EZL) on drivers side fender well under hood.

 

[waybomb]

Ok, this car starts fine. Takes quite a bit of juice to turn the engine over. One <could> assume the battery would be good if the engine cranked over normally and started.

NOT!

This problem was caused by a bad Battery!

 

[mvmiller]

I am glad you found the problem.

 

[waybomb]

Problem not found - SOS

This is my kid's car. Here's the entire serious of checks and the symptoms. I haven't worked on the car at all; I got all my info from Kev, my son.

The first thing I told him to check was the fuel filter. He did, and it was partially clogged. he replaced it.

He then told me no fuel was coming out of the tank. I told him to look at the repair cd's to make sure he was looking at the correct line. He's too smart to do that, so he pulls the tank. It was clean, the screen was clean, he was checking at the fuel filter outlet. The line coming from the tank flows fuel freely.

I am sure this is not a fuel problem.

He had the car at a buddy's shop. They put a real battery load tester on the battery and it failed miserably. Replace battery. Thats seemed to help. He went to pick up the car and a block away from the shop, the car dies again.

They test the alternator. It is marginal. They replace the marginal alternator. Seems fine, until he drives away.

So now I get involved and visit the place he has the car.

here's how it goes:

Cold start, fires right up, idles fine, and at around 50c coolant temperature or so, the idle jumps up to about 2200 rpm or so. It runs like this for anywhere from 15-45 seconds, then abruptly shuts off. It doesn't spool down slowly; it shuts off.

If restarted immediately, it jumps up in rpm almost bright away, and dies after about 15 seconds.

While in this process, I sprayed started fluid into the air valve. The engine did not pick up at all in RPMs and died. So, something electrical.

What could cause the engine to shut down electrically AND cause the rpms to jump up for 15-45 seconds? Does anybody here have the suspect controller we could borrow and try out, and then buy if needed?

If after the first event, the car is allowed to cool down, it takes longer for the process to occur. So, somehow, this is related to coolant temperatureas well.

He had a known good OVP and tried it. Nope.

What do you think the issue could be? I am not around to help him, but I'd like to save him some money. He's going to tow it to a Euro-car repair place. I can just see the $$ racking up and he doesn't save money like kids should.

 

[ElRojo]

I'm gonna stab at three possibilities-- first and cheapest is the idle control relay, found beneath the false wall in the passenger footwell. I'm pretty sure you'll want to replace that to start with, although it might not be the issue. The fact that is jumps to 2200 when it goes to "closed loop" after a warm-up makes me think it's worth a try though. I'm pretty sure you want P/N 004 545 1032. I have several of these available.

Second is the fuel pump relay, which is found between the two firewalls in the engine bay. I have a few of these lying around-- see which numbers are on yours-- it should be something like 002 545 9205, and it will often have "KPR" or "KVS" on it (not Klima). Pull it and count how many pins it has on it.

The last would be the KE jetronic controller, found on the outer wall of the passenger footwell, behind the carpet. Be careful taking the carpet away-- the plastic it's applied to gets very brittle. I have two of these lying around- #006 545 6032 and #008 545 5232. See if your numbers match.

I'm pretty sure one of us So Cal junkyard divers can get all of these units for you in relatively short order, and pretty inexpensively. As I said, I have a bunch of parts around. If you need something that I don't have, a JY run might be in order. I'm laid up for a couple more weeks after foot surgery, otherwise I'd be out there scrounging, once the water dries up from the recent rains. Mclare (on this forum) might have bits lying around as well-- you can PM him.

 

[waybomb]

Thanks for the reply. My son "newbenz2" just registered here, so hopefully he'll contact you about the parts.
He says that the fuel pressure was checked today. When the car is running, the fuel pressure is something like 100 psi. When this failure process starts, the pressure drops to 45psi.
I am not sure where they checked it, but I forwarded a PDF I found on this site that outlines how to check fuel pressure. I'm sure he'll follow that procedure.

Any thoughts?

 

[mvmiller]

Here are the fuel pressure specifications for the 420 engine:

System Pressures:


Cold or Warm 6.2 - 6.4 bar (90 - 93 psi.)

Residual Pressure, after 30 Min. 2.8 bar (40.5 psi.)

Lower Chamber Pressures:
Presure specifications given are in bar (psi) below previously measured system pressure.


Normal Operating Temp. 0.4 bar (5.8 psi.)

Idling 68°F (20°C) 0.5 bar (7.3 psi.)

Enrichment Pressures:
Measured at lower chamber port.


Acceleration Enrichment 20°C (68°F) min. 3.8 bar (55 psi.)

Deceleration Pressure:
Measured at lower chamber port.


Decel Pressure Must equal system pressure

 

[waybomb]

Looks like all the various checks are ok, until the idle races. It then drops to 45psi.

Elrojo, I sent a PM to you and mclare about the parts.


Here's some pof what I sent:

He has the car at a friend's dad's shop, but they are not familair with Benz. They have been doing a lot of searching here, mbworld, mercedesforum, and peachparts, plus, they ahve aldata.

They have determined the issue to be either the fuel pump relay or the OVP. Elrojo suggested the idle control , the Fuel pump relay, and a control under the pax carpet

I was hoping that one of you had extra working used parts, or, between the two of you, the parts.

I hate throwing parts at it, but looks like the thing to do at this time as I am out of town and can't help. Even though on this one, I am lost.

 

[jaymanek]

My 560 has been playing up too.. mine just cuts out at low revs, when approaching a junction... When restarting the fuel pump doesnt buzz at all.. I played around with a few things, tried a new fuel relay but no good..

Could it still be the idle relay?

It hasnt done it in a while but I know it will come back to haunt me at the worst possible time.

 

[mvmiller]

The racing idle just before it stalls could be unmetered air getting into the intake system. Check the following air plenums on top of the engine for leaks or cracks. Especially check the idle control valve hose connections as well as the injector plenums.
This whole system runs off of pressure differential. Very little electrical controls.

 

[waybomb]

Thanks everybody for staying with us through this. My son is working on this issue without my being there.

Thank you ElRojo and Mclare for trying to find some parts for us.


Here's what he tells me today. If the problem occurs, and the cars dies, and the engine is restarted, it will race and die again, as stated above,

He swapped the OVP out, the Fuel pressure relay out, and some other controls out, same problem. Then he jumpered the fuel pump relay. No more problem.

So, something is dropping out the run signal to the relay.

Any ideas????

Again, thanks everybody!!!!!!!

 

[ElRojo]

If jumpering the FPR allows the car to run, then that to me means the FPR he used is faulty (the jumper simply bypasses the relay circuitry). Was the FPR he put in a new one or a used one? I'd go for another FPR try.

 

[waybomb]

He used one from an alledged running car that is being parted out.

Any idea what all controls the FPR and the items in series with the control? If it were a simple relay, it would only need 4 pins - control +, control -, power supply in +, and power supply out +.

I just spoke with my son and they are tracing it out now, but any guidance would be appreciated. They are using aldata schematics, but none are experienced techs.

And the FPR came from a known reputable source. I am guessing it is not the FPR. What is odd is increase in idle for a while before it dies. It runs at a high rpm (2000-2500) for at least 5 seconds before it dies. When I was in town and stopped by a couple of weks ago, it ran at high idle for a good 20 seconds before it quit.

When it started to quit, I sprayed ether into the throttle hole with no increase in idle. Kinda leading me to beileve it is electrical in nature. If it still had spark, but no fuel, the ether should have kept it running. Or not? When jumpered, does the FPR feed current to anything else?

 

[newbenz2]

Hey everyone, we unplugged the idle control and it still does the rev and die. If you spray starting fluid it will keep running though.. We jumped the relay and it stayed running. Any Ideas?

 

[newbenz2]

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...

 

[waybomb]

Glad you made it here Kev.

You NEED to get a list of what was checked and post it here.


Everybody else, on this current thread in the 126 section :
"http://www.benzworld.org/forums/w126-s-se-sec-sel-sd/1495041-rediculously-underpowered-accerlation-getting-desperate.html"

they talk about grounding out the temperature valve that puts the system into closed loop. Kev's car seems to only exhibit the symptoms once its reach about 50c.

Why would the FPR be cut off once it goes into closed loop?
Anybody?

 

[waybomb]

Kev,
Now the engine runs on starting fluid when it does the dying thing???

<Could> it be possible the new-used FPR you got was also bad?

Take one of the two apart and resolder all the connections. Maybe your bud can do that while you are at work tomorrow?

 

[waybomb]

Can somebody send or point me to a resource that would list the appropriate values for the pinout of the FPR socket, in cold mode and closed loop?

 

[waybomb]

ttt

Anybody?