Non-starter 107 (and technical overconfidence)
 

I got called for help with a non-starting '83 380SL three years ago. Cranked endlessly, but would not ignite and run. After checking the forums here, the problem was worked down rapidly and correctly to a failed fuel pump relay. Bravo, M-shop posters! You prevented a tow-in. I fixed it where it had failed.

Yesterday, same car, same symptom, this time while the car was up on ramps in the driveway for a coolant change.

I instantly said, "Must be the same thing as last time, fuel pump relay, easy fix," while patting myself on the back.

Uh, nope. I jumpered the pins on the relay to get the pump running, and still no start.

Fuel level was quite low. I figured that it *had* to be a case of a dry pickup in the tank starving the pump because of the ramp angle. Went and fetched a big can of fresh gas.

Nope. Uh, does the fuel pump run? Seems to do so. I can hear it when I jumper the fuel pump relay.

Battery good? Better than good. Doing great. Turning out more cold cranking amps than a cheap Exide ought to be able to.

Distributor okay? Yep. Clean under the cap, only minor wear, rotor looks fine. No moisture inside or outside.

Is there spark? Pull a cylinder wire and check while turning over. Yep, seems strong. At least that one cylinder should fire.

Starter solenoid engaging? Yes, the engine happily spins all the stuff at its front.

Metering plate stuck? I pulled the airbox and checked. No.

Geez, for a guy who was confident he had it nailed right away, I'm pretty confused now.

The car will crank until battery exhaustion (I have a charger on it in between start attempts, to prevent deep discharge).

Yesterday, it cranked with no hint of ignition. Today, it coughs a little roughly, as though it's considering starting. I tried pouring a bit of fuel directly past the metering plate. Nothing.

Any hotter wrenches than I am care to take a shot at diagnosis? Am trying to tell myself that it's not a sick fuel distributor.

s/b

Crud from the low tank plugged the fuel filter or tank pickup screen? Check for actual pump flow at the engine. I wouldn't expect much pouring fuel down the air intake if the injectors have no flow.

If you confirm a spray at the injectors and spark, then you might be missing compression, eg if the chain is loose and jumped a tooth.

Steve

Put a pressure gauge on it and check the fuel pressure. It might still be the pumps or the check valves.

I can't recall where the pickup is on this tank, but yeah, that is entirely plausible. I certainly ought to hope for a plugged filter; if the filter sacrificed itself to protect the fuel distributor, that's *much* cheaper.

Quote:

Check for actual pump flow at the engine. I wouldn't expect much pouring fuel down the air intake if the injectors have no flow.

Going to try again this weekend with starting fluid.

As for verifying pump flow, I figure I could disconnect the feed line into the distributor, route it to a bottle, and jump the relay.

Quote:

If you confirm a spray at the injectors and spark, then you might be missing compression, eg if the chain is loose and jumped a tooth. Steve

This engine is (by the receipts) only about 30K since a full rebuild, including a double-row chain, and I wouldn't figure it to be loose already.

But the rebuild seems to have been a half-assed job -- compression is weaker than I would expect, 160-170 range, and visual assay of the timing chain guide rail shows it to be bottle-brown (geez, could they have re-used the rail?).

I'm not hearing any mechanical-catastrophe noises when turning it over, so I'll assume for now that even if it's off a tooth, trying to start with starter fluid is okay.

Thanks for the feedback; I'll follow up shortly.

s/b

I agree with the fuel theory.

I would verify fuel by cracking a line on the fuel distributor with the fuel pump on, then quickly closing it to avoid spillage.

Even if you have jumped a tooth, the engine should still fire.

If I am not mistaken, does the anti-theft system have a tow switch that when the car is "lifted up" such as a tow truck would, that it disables the car?

No antitheft on this car, but it's a good hypothesis in cars that do!

Latest update: I went out to the car today, and before anything else, tried starting it. Varoom! Instant start, clean idle.

Completely baffled by this one. My experience has been that ignition problems sometimes self-heal with some time spent sitting (wet distributors and the like), but the electricals were dry and tested on this car. I was pretty sure it was a fuel issue. Sounds like most of you who responded were also focused on fuel as a cause.

I shut the engine off quickly, as the block does not yet have coolant in it (the car was on the ramps for a block drain and coolant change). Further diagnostics will have to wait until after the coolant is in.

My next chore is to figure out how to refill the block on a 380 engine. The service CD for the 107 cars describes some crazy gig involving jumpering the auxiliary (heater) coolant pump -- there must be a more sensible way!

s/b

Nope, you gotta get the heater core full or it gurgles and burps air forever, leading to having to fill the coolant tank multiple times.

You can simply put the defrost on with max heat, I think, but even so, with warm air temps, the aux pump may not run, so no wate rwill go though the heater core.

Follow the procedure, it's there for a reason.

I have to bleed the air out of the 280 SE by opening one heater hose at the heater core, it won't push the air out under water pump pressure, and the heater cover gets airlocked -- no heat.

Peter

Ah! So the manual authors did know what they were doing! Makes perfect sense. Thanks, Peter.

But, correct me if I'm wrong, goosing the aux pump to force turnover of the heater core contents is something that should happen after coolant is already in the block, nicht?

So it turns out there *already* is coolant in the block, to my surprise. See my separate post in Tech Help about "teleporting coolant".

s/b

Unless you pull the drain plugs in the block, with the water pump installed, the block will contain water almost up to the top of the "V" in the center -- as i discovered while sealing the cracks the idiot PO caused on my 280SE by not putting anitfreeze in it when the water pump leaked.....

Peter

Ouch! What an awful thing to allow to happen to a great car. Yeah, you have my sympathies, I'm in PO hell right now.

Well, at least on the 380. The 500E had a *great* PO who seems to have done everything professionally, by the book, and on time. I can't find a single thing to ***** him out about. Wish that they were all that way.

I have to say that I was very impressed with the volume of fluid that came forth from both block drains. Easily the volumetric equal of the rad and expansion tank combined.

Note to future wrenchers who may find this thread -- you really should pull both block drains if you want to get everything. I pulled the PS plug first, and then DS a few minutes later after PS stopped flowing, and got a big immediate rush of water from the DS plug. By no means does it all come out from only one of the drains.

s/b

Final followup on this one:

Assumed to be fuel starvation due to something blocking the tank pickup. Once it began to start again, it has done so consistently and reliably, and it has run with no stumbles and plenty of power.

My best guess matches what someone else suggested upthread: that because of the low fuel level and the severe incline of the car, a big piece of rust or other crud in the tank managed to occlude the outflow.

I thought that my refilling the tank partway and vigorously agitating the car by jumping on the bumper would knock loose any debris. Perhaps it did, in retrospect -- the car didn't start instantly after I did that, but I only cranked it for thirty seconds or so. It did start the next morning.

s/b