240 '84 another no-start thread

[mels]

Gents,

1984 245 NA

Had an issue over the past year where the engine would just out of the blue quit clean without stumbling or any warning.

Could usually slip it into neutral and it would restart on the fly. The past couple weeks I noticed the car wouldn't accelerate cold as quickly as it usually does once warmed up, just figured I wasn't giving the old girl enough time to wake up.

Heading Home from work yesterday engine again quit suddenly while on the highway. Tried the old pop it into neutral and restart trick but to no avail. Coasted off to the shoulder, waited a few moments then she fired right up. Made it Home, had to run out again and on my way home engine stopped suddenly, again. Everything else works fine, lights horn blower radio starter cranks engine over at a good clip (newish battery), darned thing just won't start, won't run.

Flatbed hauled her Home.

Seemed to me to be like an ignition problem the way she just cuts right off clean with no stumble so I looked into that first. Got good spark.

Unplugged AMM thinking maybe just maybe it had something to do with that but of course as is my luck, no change.

So I turned to searching this forum, read up a lot and while I didn't find any threads that matched exactly my once intermittent now more permanent problem, I did find some helpful leads.

Armed with those leads, I spun fuses, changed my blinker fluid (11wt because it's below freezing out) turned the radio to NPR well, because that seemed like the thing to do, again no change.

Grabbed my meter and started reading voltages on both sides of the fuseholders with the key in the run position, and that's where I found what could be my most solid clue thusfar: no power at fuse no. 5 (in-tank fuel pump). Now, heretofore I had discounted a fuel problem simply because I can hear the main pump run, hadn't considered the lift pump.

Now my questions are these: does the fuel pump relay send power through fuse no. 5 and on to that pump, or does power go through the fuse first then to the relay and out to the pump?

If power runs through the relay first, then would I be correct in assuming the relay has given up the ghost?

Sorry if this has been covered ad nauseum, i just couldn't seem to find an answer I could sink my teeth into.

Also, if leaning towards the fuel pump relay, where is that sucker located? I've filed my owners manual in a safe place so I wouldn't lose it but you know what happens when we do that...

Thanks in advance for your help, we need to get this car back in service ASAP and we can't blow the coin just throwing parts at it.

 

[cleanflametrap]

Now my questions are these: does the fuel pump relay send power through fuse no. 5 and on to that pump, or does power go through the fuse first then to the relay and out to the pump?

Yup. Exactly. Relay takes the juice from the red lead and the 25A blade fuse and delivers it here to fuse 5 - left side to the main pump, and right side to the tank pump. It only does so while cranking or running, not just key on. If you have spark indeed, and nothing on fuse 5 while cranking, suspect the 25A blade fuse wiring. Yes, the wiring, not the fuse itself.

If power runs through the relay first, then would I be correct in assuming the relay has given up the ghost?

No. Unless someone turned the relay upside down and a windshield leak followed the harness inside and rusted it, the relay will outlast the car and maybe even you. Very reliable metal can Bosch relay.

Also, if leaning towards the fuel pump relay, where is that sucker located?

It and its lookalike, the System Relay are above the passenger's feet. The red wires you see on their sockets come from that crusty 25A blade fuse where I would look for your trouble.

 

[mels]

Art,

Thanks for your reply, and the direction. I should have mentioned that I had checked that 25a blade fuse (engine compartment, drivers' side fender in front of the strut tower) for continuity (pulled) but not for presence of voltage in the wiring up or downstream. Will hit that hard tomorrow.

Thanks too for the clarification on voltage presence (or lack of) at fuse no. 5 while cranking rather than key simply in the run position. It was while cranking that I checked for voltage at fuse no. 5, no dice.

Where should I look for the 25a blade fuse wiring to run, and terminate at each end?

 

[cleanflametrap]

Where should I look for the 25a blade fuse wiring to run, and terminate at each end?

The source should be the bus (junction block) screwed to a bracket along with the high/low headlight relay on the left fender, but it is a long time since 84, and many were moved to the battery terminal. The fuseholder itself is a piece of work with 6 separate connections to corrode, so it may now be a patched in pigtail version.

The load is terminal 30 of both of the relays I mentioned inside the cabin. The best way to be sure this circuit does not have a piece of green crud in it somewhere is to read one of the voltages provided by a relay downstream. The system relay powers up the AMM, so because it is handy, provides a decent load, and universal across years of LH-jet, I roll the boot back on the AMM and check for battery voltage on the orange (power) lead. If you have it there key on, the red lead is good.

Ignore the red stuff... Also, this matches 1983 - in 84 they moved fuse 12's FI function to fuse 13.

 

[mels]

Roger that! Some good intel there Art, I'll dig into that and make my way back here after.

 

[quillc]

I've had two relays go bad on my 83 over the 150K miles I've been driving it. I keep a spare in my trunk for good measure these days.