DME relay for fuel pump question

[Tim Boyer]

HI,
I am trouble shooting to find out why my early 85 is not starting. It has been sitting for a while so I am thinking fuel. Can someone tell me how you would know if you would have a bad DME relay for the fuel pump?
Thanks,
Tim

[John_AZ]

Make a jumper:

DME Relay Information and Testing

If the jumper works...................the DME relay could be the problem.

GL
John

[ERAU944]

how long is 'awhile'? inside a garage or outside? temps?

there can be a bunch of issues that might cause you a problem after a long storage, so maybe we can help you systematically narrow it down.

i'm ashamed to say it, but my cars sometimes sit for 5-6 months at a time. always in a garage, and as such temps never get much over 100 degrees F.

when you're just beginning to troubleshoot, start with the big 3:
Compression
Spark
Fuel

If your car doesn't sound like a sewing machine while you're trying to start (i.e. the timing belt has broken and all you're spinning is the crank) then you can safely assume that the compression is good.

to check the spark, the easiest thing to do is hold a spare spark plug connected to one of the wires and hold the business end of the plug against the head or intake manifold and make sure you've got a nice blue spark.

to check fuel gets a bit messier and more complicated: without having to pull the injectors out, pull the plug off one of the injectors and see if you are getting a signal while cranking.

if you are getting a signal to the injectors, make sure the pump is working. if it appears that the injectors aren't opening well, you can try to 'wake them up' by tapping with the PLASTIC END of a screwdriver (tap the other end gently with a hammer and use the plastic end to give them a soft jarring).

i woke up a parts car one time by jarring the injectors. the car had sat for years, and the car wasn't in any shape to go anywhere. got it trying to start with some raw gas in the intake, and eventually after some persuasion the injectors decided they wanted to do their thing properly.. It's not typical for them to get gummed up from just sitting, but if you have a bad drain back valve in the fuel system it's possible.

oh, and to answer your question in the original post: you know it's bad by either testing it, or swapping in a good unit (typically the one you have as a spare that you keep in the car. you do keep a spare in the car, right?)

[Tim Boyer]

Thanks for the suggestions. I will try all of them and hopefully wake this beast.
Tim

[Cocacolakidd]

The 944 motor is an interference motor - That means if the timing belt is broken and you are spinning it over and the crank is spinning, and pistons are going up and down, but the cam is not spinning. That means that the pistons come up and hit and bend the valves - sometimes destroying valves and even destroying the head. Interference motors will bang the valves into the pistons if all is not well with the timing belt.

If you already have been spinning the motor over by the ignition key, and the motor has not gone crunch, bang, snap and crinkle - Next with the ignition key off watch the Tachometer closely and turn on the Key and watch for Tach bounce, very slight, maybe a 1/16" or so. If there is no Tach bounce then either the reference sensors are out, or the DME (Motor Computer) may have a problem. If there is Tach bounce then it is fuel or spark.

Turn on the key and listen for a slight hum of the fuel pump. If you do not hear it check out the link for the DME relay (Listed above and a good source - Clark's Garage), and check this out first.

Check to see if there are 12 Volts to the coil and spark plugs with the loose spark plug method (As long as you know know that the timing belt is intact).

You can also slightly loosen the front nut on the front of the fuel rail slowly with the key on to see if there is fuel pressure there - if so there will be a fuel leak (Make sure to clean up fuel if spilled).

All of the above is a process of elimination, and the first thing is to eliminate the possibility of a bad timing belt (Very important).

To check for bad fuel - spray a little starting fluid into the air intake below the air filter. If the car starts shortly and runs out of starting fluid then you have a fuel problem...