Spark but no fire

[tluz]

Hi, Guys,

New to the Forum but not to Spiders. Had a '74 years ago but tinworm got it. 'Nother story.

Hope you can suggest a way to diagnose a problem.

I have an '82, manual, injected but not turbocharged. I unwrapped it after its winter's nap yesterday and took it out for a spin. It fired right up, warmed up like usual and sang beautifully for about 20 minutes. Rowed up and down through the gears and drove about 10 miles or so. Then it started to bog on acceleration. It would get there, but not quickly. The idle got rougher and rougher, then it just quit. The battery was charged and it had fresh gas in the tank.

Repeated cranking has not resulted in ignition. So I started testing stuff.

Test light with the key in the "on" position shows power to the coil, and pulling the high-voltage wire from the distributor and grounding it while cranking shows a good rhythmic spark. During this process my hand also discovered that the spark is pretty strong. So the issue does not appear to be with the engine control module. With the key in the "on" position the whir of the fuel pump is faintly audible, so I'm guessing there's fuel reaching the engine, but I have not actually tested it.

Last year it had a problem with bogging and it turned out to be the throttle body adjusting screw. I tightened it about 3/4 of
a turn, sealed up the box with gasket maker and had no further problems.

Have any of you experienced anything like this? Any ideas or suggestions would be appreciated.

So now I'm puzzling about what to do next. Is air sneaking in behind the throttle body? Bad O2 sensor? A relay? Fuel starvation?

Any suggestions or ideas would be greatly appreciated.

Best,

Tom

[So Cal Mark]

the fuel pump shouldn't run until the afm flap opens. perhaps the flap is stuck open

[tluz]

Thanks, Mark. By AFM, do you mean "Air Flow Sensor"?

[SLOSpider]

Yes the air flow door on top of the air cleaner, check that it is not stuck open. Fuel pump only runs when cranking engine that pulls air in and opens that door then makes the fuel pump come on via a switch inside the mas air flow sensor.

[tluz]

OK, I pulled the unit off the air cleaner and found an L shaped, spring-loaded flap inside. It is not hung up and moves freely when pushed. Snaps back when let go.

Interestingly, even with the power to the AFM disconnected, when the key is in the "on" position the fuel pump is buzzing. Bad pump relay in the relay set? Or bad pump?

[RRoller123]

Probably was wired to be on all the time, which was common with these cars. Mine is that way. Apparently the damned FP relay is failure prone, so PO's would bypass it. You can make it all safer by installing a crash inertial switch to shut it off in the event of a serious collision. Don't want fuel being pumped onto a crash scene if the ignition switch stays on and you are unconscious, for example. A very bad result could occur. The inside of the AFM module would have the contact arm bent like in the pic below if the fuel pump on/off is NOT being controlled by the AFM module (this is the way mine is, from PO)



See how the pin is bent to the left so that when the AFM is closed it does not make contact with the brass piece? The FP is then wired to bypass the relay and just come on automatically when the ignition switch is on. This is only sort of ok, but it would be a lot safer if you add an inertial shutoff switch to the system.

[So Cal Mark]

it's possible the wire that connects to the - side of the coil fell off. That would interupt the ignition signal to the ecu and the injectors won't pulse.
If someone tweaks the afm adjustment, the fuel pump contact won't work properly. It's not a big deal to bend the arm to open the switch when the flap is closed. That way the pump won't run constantly

[majicwrench]

You need to actually verify fuel getting to engine. Pump running w engine off is not correct, but no biggie. Easy first step is piss some fuel down a vacuum hose and see if it runs on that.
Keith

[tluz]

good ideas, guys, thanks. I'll check the - side of the coil and see if it will start with fuel poured in.