Hello, I've been pulling my hair out, and searching the net frantically. This forum kept popping up and seems to have good advise so I joined, I hope ya'll can help me out on my 1988 740 gle non turbo botch system.

This car is fairly new to us, we have put about 10k+ miles on it and it now reads 190K or so. We have had some fuel issues in the past, and that is partly why I'm leaning to the fuel for why it's not starting.

A few years ago it would run and randomly die, we took it our mechanic (no longer dealing with him, and inspired me to learn to work on our own cars) and he said that since the car had been sitting for so long that the tank was all rusty, and plugging up the fuel system. He replaced the fuel filter and it ran fine. This past summer it has been out primary family car, and we have been driving it a lot more. This past july the car died on us on a road trip. It was hot, driving up a steep grade, and the car sputtered out and died. It would not start back up right away, and it finally started after I opened the gas cap (to listen for the fuel pump, couldn't hear it (on highway). We got it to the next town, added some sea foam, and filled the tank thinking it may be the in tank pump. It got us home, and has been fine ever since.

A few days ago it died as I was accelerating the oil light flicked on, and the engine stopped running. It has oil, full tank of fuel, and battery. It will not start, and just cranks, I cannot hear the fuel pump comming on. I then went online and started reading up. I tore into the fuel pump relay, and that's where I'm stumped. I jumped the #30 slot to #87 and the main pump comes on. I tried cranking and no start, replaced the relay, and no start. I fildled around and got the pump to work once (very briefly) with jiggling the relay. I can't tell if the pre pump is working or not but I do have a full tank so shouldn't the main pump be enough? Should the car start when I have the relay bypassed? I can't figure out why the pump works when the relay is by passed, and the relay won't click the pump on? Is the relay I bought bad?
I also took the radio suppression relay cover off and it appears to be working just fine. I also cracked open the fuel line at the injectors, and a little fuel leaked out (but not much more than a few drops) as I had some one else crank the engine.

I guess I'll leave it here for now. Any help would be appreciated for this broke aspiring diy mechanic.

 

Spray some starting fluid and you'll know if it's fuel or spark....
Year?
Oh, and the less you "tear up" now, the easier it will be later to get it fixed...

 

wait. 'cracked open the fuel line at the injectors' ? I wanna scream STOP, DONT TOUCH THAT CAR. this way leads to engine fires, and nothing good ever comes from that

 

the fuel pump relay is a dual relay, one half powers the ECU and the other part powers the pumps. so, if you've unplugged the relay and jumped the fuel pumps, you'd also need to jump the other side (87/1 and 87/2 are the two halves) so the ECU would be alive and the car could start.

 

Thanks for the saftey tip, and just for a little clarification I checked fuel where the rubber gas line meets the steel one near the injectors. Every thing was cold, and it was right after the engine was cranked to see if there was any pressure. Since the fuel pump was not coming on I took that risk to see if there was enough gas to at least make the engine stumble or try to start. I'd swear it's a fuel issue, but I'll test for spark tonight after work just to rule it out.

 

It's a 1988

 

Ok just a short up date.
I tried the double jump on the fuel pump relay and nothing. With the new relay in, turning the key very slowly from I to II I can some times hear the pump kick on for about a 1/2 second. Is there some sort of fuel pressure sensor that tells the pump that there is enough fuel pressure and that all is well? Given the history I went to fuel to check fuel 1st, and since I can only hear the pump kick on once every dozen attempts (while jumped it's all on all the time, as to expect). When the relay cover is off the relay on the right (if it's facing you) clicks on, and the relay on the water expansion tank is working too.

Off to check spark after work tomorrow... Could it be in the ECU or ignition?

 

the pumps should run about 1 second when the ECU is first switched on, then it waits for pulses from the Hall sensor in the distributor to tell it the engine is moving, before it turns the pumps back on.

LH2.2, the primary sensors are the MAF telling it how much air is being sucked in, and the engine coolant sensor telling it how warm the engine is, and the pulses from the hall sensor telling it how fast the engine is going. it also monitors the O2 sensor for lambda trim, and the idle switch on the throttle to know when to regulate the idle.

the hall sensor is actually wired to the ICU first, and the ICU outputs the timing pulses that the ECU sees.

 

Well this keeps getting deeper. No spark (at coil).. I'm finding bad wires, and when I checked fuses it was for the fuel system. I pulled all fuses one at a time, and the big 30 amp fuse in #16 to the heater/ac is welded in place. I traced one of the wires that relay which is corroded and has some black sooty stuff on the prongs. This is my familys main ride (the other is a toyota R20 truck that I use for work), I may be throwing in the towel on this car...

 

It turns out that it was the timing belt... I did have fried wires under the fuses, but I think that they are all on unrelated circuits, and they are now fixed. I still may have a fuel pump/relay issue since the fuel pump will not prime with the key on II... We'll see once I get the new belt and harmonic balancer in.

 

740 GLE has dual overhead cams, correct? This may be worse news as the DOHC engine is interference engine. May have bent valves.

 

'88 GLE does not have an interference engine. That designation later applied to 16v motors.

 

well she is alive, not well but alive. New timing belt and balancer on, it seems to be a little spunkier now (might be in my head). I must have done something to the wires, while fixing the heater fuse, and some burnt wires.... No horn, power mirrors, radio, and possibly wipers (motor was going out anyway)

 

I'd check the fuses first. otherwise, not sure what could tie those things together, except maybe ignition switch accessory power.

I don't have the schematic for 88, just 91+, and those are a bunch of transition years so I can't analyze the wiring to see if there's a common point for your failures.

 

Just as a note, my LH2.2 car (1989 740) never primes the pump until the engine is cranking. I wouldn't worry about that.

Look in the fuse box table and see if your missing accessories are on common fuses and then check for power with a multimeter.

 

yeah, our 87 240DL, also LH 2.2, doesn't seem to prime the pumps. Its probably the ECU you have that determines this.

my 1992 740 turbo, LH 2.4, definitely DOES prime the pumps. if you switch it on /then/ start, it starts faster/easier than if you just crank it from off to start quickly, but either way it starts in about a one-one-thousand crank.

 

That's ignition switch problem. Turn the key slightly, jiggle it, those accessories should come on.

 

Fuses are good... I had the whole underside of the dash off tracing wires since that was where the burnt wires were.... On both sides of the #25 (rear fog lamps) the wires insulation on the wires were fried. I think that this was a old problem since some on removed that fuse, and the fog light switch never worked since I have owned the car. I never really cared about not having the lights, so never looked into it. Also the big 30 amp fuse going to the heater was melted in place, the fuse never went but I couldn't get it out.

I spliced in good wire on #25, installed a in line fuse, and did the same for #30. I'm just worried that I some how did something to the other circuits. I don't see how I could.

Since the heater fuse is right beside the others (see below) do they share a common hot wire under the fuse panel? If that's so that would be it! I do remember when I was doing all the cranking to check the fuel pump and ect that the radio would come on... I just don't have a cause and effect moment when I was in the wires.



14 Electrically-operated side view mirrors, cigarette lighter, radio, rear wiper (wagon) 15
15 Horn, windshield wash/wipe 25
16 Heater blower, air conditioning 30

has to be somthing simple... Thanks for the help

 

the 740/940 fuse panel has a couple common rails, these are brass strips on the bottom side of the fuse panel, at least one is the always-on power, and another is the ignition switched power, and of course there's a ground rail too.

 

Well I think I have every thing as it should. I spliced "jumper wires" back into the dead #16 fuse location, and #15 and #14 are back on and working fine. What a frustrating learning experience, now I think that I would never want to get rit of this car since I know it literally inside and out now. Thanks for the help that I got here