I have been monkeying around with my daughters 1988 240DL all summer trying to deal with starting issues. After sitting, it cranks for a long time before firing then when it finally goes it is froggy for 10-15 seconds and then fires up. Once it's running it runs like a top.

So far I have replaced the in-tank fuel pump, flame trap, cleaned the throttle body, replaced the spark plugs, distributor cap, and fuel pump relay. I have also run some fuel injector cleaner through the system.

It seems to run lean rather than rich in that I don't get a gas smell when pumping the gas pedal a little to help things along. I can hear the rear pump humming when the car is running and the main fuel pump loud and clear. I guess my next main suspect is the fuel filter but I would think that would be causing problems even after the car is running.

Don't think these could be related but I will add that I replaced the radiator in the spring and when the car gets real hot it spits a little coolant out by the water pump. I've ordered a new pump but can't see how these would relate to the starting issue. The oil looks fine in that I don't see any signs of coolant mixed in.

I don't have a fuel pressure gauge and maybe I need to invest in one. Does any one else have any ideas on what to look at next?

 

Textbook Coolant Temperature Sensor failure symptoms.

 

Wow. Thanks. That is about the last thing I would have thought of. So the cooling system issues are likely related. It looks like that will be a bit of a bugger to get at. May have to pick up some ratchet extensions.

 

the coolant temp sensor is used to tell the ICU and ECU how hot the motor is so it knows how much fuel and what spark timing to use. if it doesn't know the engine is cold, it won't richen the mix, making it quite hard to start.

 

Actually, a COOLANT LEAK has nothing to do with the SENSOR unless the coolant level is so low that it affects it... but it has to be really low. Your case doesn't sound like it. A little pump seepage is not that relevant.

 

Update on this issue. Last weekend I pulled the intake manifold and replaced the engine coolant temp sensor as recommended in this thread. I also replace the knock sensor which had completely snapped off. The ECT sensor snapped of like nothing when I touched it so it definitely needed replacing. Now with these two sensors and a new intake gasket, things are running smoother than ever.

However the issue with extended cranking after sitting for a while has not gone away. I should probably just spring for a fuel pressure gauge kit but my next suspicion is the fuel pump check valve. However, when I reach under and feel the valve when the car is running or just after, I am not feeling any fuel.

If the valve is leaking, would the fuel typically be leaking externally or just back into the feed line?

Another question. The main fuel line to the fuel rail is very loose and can be slid and a half inch or so either way. This is similar to my other 240 so I'm thinking this is typical. Do I run any risk by clamping this down to make sure fuel isn't vaporizing out of the line?

 

Is the fuel pump priming when the key is turned?
A fuel injected engine should not need the gas pedal pumped. It does not act like a carb.
If your main pump is "loud and clear", then it is likely that your in-tank pump is not operating. A failed pre-pump is a likely cause of hard starting and initial poor running.

 

Thanks fochs. I replaced the in take pump a few months ago and I can hear it running when the car is running so I'm confident this is not the issue. As far as the pumps priming, my pumps do not start running until the starter cranks and I have heard mixed opinions about whether this temp priming process when the ignition is turned on exists on earlier models. However if this priming process should indeed happen on a 1988 with an 1984 engine then I am open to suggestions on what may be causing it not to happen. I also replaced the fuel pump relay at the time I replaced the in-tank pump.

 

clip a test light one side of the tank fuel pump fuse (I think its fuse 4?) and a handy ground, and see if this light comes on for a second when you turn the key on.

the fuel check valve is just a one-way valve, it keeps fuel from going backwards into the pump.

i'm unclear what you mean when you say the fuel line moves an inch. is that side to side?

 

It can slide up and down its connection about a half inch away and towards the fuel rail. When I try to pull it off completely, it gives plenty of resistance to the point where I did not force it all the way off so I'm assuming that the connection may be designed that way. It does not appear to have ever had a clamp on it and my other daughtes 91 240 is the same way. I did not take it all the way off the fuel rail connection because I wasn't familiar enough with the connection to risk it but it seemed strange.

 

Absolutely the pump should prime both on an '84 and an '88. Prime it manually a couple seconds by jumping a wire between the 30 and 87 positions on the relay socket. Those are the larger slot which is sideways and the slot directly across from it. Alternatively, you can jumper the fuses to manually run the pump not sure which ones though maybe 5 and 7?. Then replace the relay and give it a try. I'll look to see about the why's of not priming. Don't know offhand. I usually have to prime my 83 twice on cold starts.

 

on a 86/87/88 240, I believe its fuses 4 jumpered to any of 6-7-8-9 (which are always powered), this should power the pumps even if the car is switched off.

if you do this and it then starts, then the lack of priming is definitely your problem.

 

Thanks guys. I will probably try and jump it using the relay socket since the fuse for the fuel pump on this vehicle is in the engine compartment.

I will post what I find.

 

so this vehicle has been rewired in nonstandard ways?!? that makes it very difficult for 3rd parties to suggest troubleshooting...

fwiw, you always want to put the fuse as close to the power source as practical. putting the fuse near the load won't protect against a short in the wire between the power source and said fuse.

 

I actually don't think this is non-standard although I should clarify. The fuse for the in-tank pump is indeed in the fuse compartment by the drivers seat. I believe it is standard for the 87-88 non-turbo models to have a 25A fuse the serves the whole fuel injection system on the left side of the engine compartment. This is where mine is located. It looks like the one at the top of this page:

Black Vinyl Wire Cover Tubing for Wire Harnesses

 

ok, yeah, thats standard. and wow, I read your statement as 'in the trunk', phew. so forget most of what I rambled. chalk it up to lack of sleep.

so yeah, jumpering power to fuse 4 WILL power both pumps, even if the fuel pump relay is turned off, even if the IGNITION is off. I'd take a bent paperclip, and touch fuse 4 to fuse 6-7-8 (which are always powered) for a second to prime the fuel system (and you should hear the pumps run), remove that jumper, THEN switch on the ignition and try to start the car

 

Great, thanks for all the info. I will try that. I will need to wait until morning after it has sat for a while to see if it speeds up the firing process.

 

Your car has the single relay (main relay) for fuel and system. If you jumper there, it is 30(red) to 87/2(yellow/red), what I posted earlier was for older models ('85 back) with a separate fuel pump and system relay. If you jumper the fuses, it is 4 and 6.

 

Just circling back to close this out. I did replace the fuel check valve with no apparent improvement. However, some other issue lead me to believe that a larger problem was at hand which all became mute after by daughter got in an accident and we junked the car. The problems started after the radiator blew, which I replace which resulted in a leaking overflow cap, which lead to a leaking water pump, which after fixed lead to a blown heater hose.

In the end, I think I had a head gasket leaking a little coolant into the intake and when it sat for a while, it just had to cough it out before it started. The symptoms sure felt like it was fuel starved but I think this was the issue. I think the head gasket leak was causing the pressure build up causing things to blow and probably choking out the start.

Thanks to those who offered advice.

 

well, the head gasket can't leak coolant into the intake manifold, but it can leak into the cylinder, or externally, usually on the exhaust side below the exhaust manifold #3 and #4 ports