84' 944-No start until pull/replace DME Relay

[JD1990]

I have a 84' 944 that will not start until I pull the DME relay and then replace it. I can do this with the original DME Relay and a fresh one I just purchased. It will start and run fine, then if I turn it off it will crank over, sound like it's firing, then does not follow through with a start.

I followed the Clarks Garage test procedures for testing the wiring where the relay plugs in and even checked it at the computer.

Any thoughts on next thing to troubleshoot?
Does this sound like a bad wiring connection?

Prior to this the car ran fine. We replaced the fuel pump recently because one of the fittings started leaking. Then did the pump and the in fuel tank filter/screen. We do get fuel to the rail.

One post suggested testing/changing out the speed and position sensors. Upon trying to test, the connectors disintegrated, so we just replaced those.

It will run fine once it does start. Just not sure the best procedure is to pull the DME relay each time.

[originalowner]

Sounds like a connection/wiring issue. You can likely just wiggle the relay instead of removing it for the same effect.

Having an Ftech9 diagnostic DME relay would help nail it down quickly. It has LEDs on the inputs and outputs of the relay, so you will be able to tell which wire is having an issue. Or, if you are handy in that way, you could add LEDs to one of your existing DME relays.

[Jfrahm]

Why not test with a jumper wire and see if you can restart then?

Do you get tach bounce when it won't start?

It might be a DME issue with the driver circuit for one part of the relay. You could also try disconnecting the battery for a minute or two and then restarting to see if de-powering the DME that way also affects starting.

[djnolan]

i would be careful about pulling the relay out too many times, it could damage the relay board. At the least put some lube on it

[walfreyydo]

Like Jfrahm mentioned, create a jumper as is clearly outlined in Clarks Garage and test. It might be wiring to/from the relay loose, so if you can replicate it with the relay bypassed, next step is to start chasing the wiring, especially the connections at the fusebox/relay

[Monkey Wrench]

small indicator bulbs might help here because you can wire them in and then see when it fails, if the DME has power and the fuel pump etc. a lamp is easier to see an intermittent issue with than a meter display.

if there is ever high power, like a short, sometimes it can get the spade connectors hot enough to loose their spring tension. that may also burn the contacts of a relay , even a new one. so you could have two bad relays if you had a pump that failed and stuck or similar and drew a higher than normal load.

if you heat brass and quench it it goes soft. if you heat it and cool slowly that may help restore the temper or "springyness" to the terminals.

you might try with a hunk of wire and a spade , press it into where the relay seats to feel the connectors on an individual basis. See if any seem to have gone soft or maybe just need a squeeze up to be tight again. hard to tell with the relay itself, as it will have more than one that seats in unison. easier to get a feel with just one wire at a time.

[JD1990]

Thanks for the feedback. I've been out of town for a week. Getting back to it now.

The remove/replace option stopped working after a few more attempts. I didn't see the concerns early enough. But also wasn't thinking it would be a permanent solution.

I suspect some wiring is loose, but will also see about jumping the circuit.

The Tac has been jumping since we got the car. Our thought was that something behind the dash was loose as we could tap the gage and often it would come back to life. (not sure how scientific the approach is)
We did replace both the speed and position sensors going into the bell housing. Still no-start. The cable connector on the sensor side just crumbled when we touched it. We did not test the continuity of the other half of the circuit. Would that be a good place to check first? or just pull down the wiring loom behind the fuses to check for loose or damaged wires (under driver side dash)?
We did get the battery tested. It tested fine and continues to crank.

[paulzebo]

If you're still stumped, I would replace your current DME relay with this one. Now you can get an indication which of the four electrical paths to concentrate on.

[walfreyydo]

Originally Posted by JD1990

Thanks for the feedback. I've been out of town for a week. Getting back to it now.

The remove/replace option stopped working after a few more attempts. I didn't see the concerns early enough. But also wasn't thinking it would be a permanent solution.

I suspect some wiring is loose, but will also see about jumping the circuit.

The Tac has been jumping since we got the car. Our thought was that something behind the dash was loose as we could tap the gage and often it would come back to life. (not sure how scientific the approach is)
We did replace both the speed and position sensors going into the bell housing. Still no-start. The cable connector on the sensor side just crumbled when we touched it. We did not test the continuity of the other half of the circuit. Would that be a good place to check first? or just pull down the wiring loom behind the fuses to check for loose or damaged wires (under driver side dash)?
We did get the battery tested. It tested fine and continues to crank.

Hi, please bypass the relay as we mentioned earlier so you can confirm whether the DME relay is bad, or if something else is the cause. Do not associate other peculiar behaviors to the no start issue until you go through the proper testing procedure.

DME relay bypass:
DME Relay Information and Testing

If the bypass doesnt work, the next thing to check is the basics - do you lack spark or do you lack fuel. This guide will lead you through the steps to diagnosing the no start issue:
https://www.clarks-garage.com/shop-manual/ts-01.htm#fire

[JD1990]

Latest update - continued with the theme that no spark or no fuel. Reading through the Clarks procedure came across one step that stated that an over-pressure of the fuel system could cause a no start as the injectors draw too much and the computer shuts them down.

The test was to disconnect one of the injectors to see if it started. All be it on 3-cyl. It took a few tries but did start, and was repeatable again with a few tries. I did have to use the jumper to get to those results. Getting it to start there points to a fuel pressure regulator issue.

Is there anything else I should be verifying?
My one concern is that I recently replaced the fuel pump. Should a new regulator be able to handle the higher pressures? Or did I get too strong of a pump by mistake?
(I am working on getting a fuel pressure gage.)

[walfreyydo]

So if you had to jump the relay in order to get it to start (even on 3 injectors), how do you know its the injector issue and not an issue with the DME relay?

Did you try starting with just the DME relay jumpered and leaving all injectors connected? If you havent done that you should. Test each system independently, dont add multiple variables.

Get a pressure gauge on the car before making any assumptions about fuel pump or FPR. A bad FPR will sometimes (but not always) have fuel leaking into the vacuum line, something you can check before getting the fuel pressure gauge.

[JD1990]

It's been a while. Following the string of looking for spark and fuel. I pulled the injectors and did a full cleaning including replacing the cap, O-rings, and "screen". I did replace the fuel pressure regulator as well (I had bought before checking the last note in this string.)
On 2nd try, after letting the fuel pump run, it fired right up. Then, as typical of late, it would not restart.

I continued back through all the checks. Confirmed the DME relay was good. Checked voltage at 18 & 35 on DME computer connector - good. And a few others.

One of the checks in the Clarks Garage Fuel-16 procedures is to check the voltage at the injector plug terminals. It says that 1 should be approx 12vdc and the other should be at 0vdc. It does not say what to do if both are reading 12vdc with the ignition on. I checked 3 of 4 injectors, all had the same problem. Thoughts? or did I read the procedure wrong.
Is there a place on the wiring harness that may be prone to issues?

Is there another test to try?
When cleaning the injectors, they all clicked when voltage was applied 12v on one side and ground on the other.

Appreciate the continued assistance.

[djnolan]

Sorry to hear you are having this problem. when it won't start try jumpering the dme relay. as you plug in the jumper listen for fuel running in the fuel rail to confirm fuel pump. now try to start it . if it won't start then check for spark by removing #1 wire, plug in an extra spark plug, with a aligator lead from the spark plug threads to ground, and then crank and observe if here is blue/white spark. remove the dme jumper afterwards so as to not leave the fuel pump running.

if there is spark this means the dme is probably ok however there have been cases where there is spark but no injector pulse due to a dme problem.

edit: constant +12V is normal on the injectors, the dme will provide the negative 12V when it pulses the injector.

The dme jumper is simply a 3-way Y connection from pin 87 (12v power) to 87b (fuel pump) and pin 30 (dme power)

More info on the Dme relay and jumper here: http://www.clarks-garage.com/shop-manual/fuel-05.htm

[walfreyydo]

Originally Posted by walfreyydo

Like Jfrahm mentioned, create a jumper as is clearly outlined in Clarks Garage and test.

Hi, please bypass the relay as we mentioned earlier

Did you try starting with just the DME relay jumpered and leaving all injectors connected?

Originally Posted by djnolan

when it won't start try jumpering the dme relay

The reason we are so insistent on this is because a bad DME relay is highly correllated with hard warm startups, because the heat causes them to not work. Once they cool down they work. The fact your thread title states that the car starts when you remove and re-plug in the DME relay, makes this the #1 theory on your issue.


YET... you still refuse to jumper the relay. The next time the car acts up, jumper the relay. Report back. Im not going to respond to this thread any further until this is done.

Confirmed the DME relay was good. Checked voltage at 18 & 35 on DME computer connector - good.

That is not how you confirm the DME relay is good.

[JD1990]

I have used the jumper. Currently I can get it to start with all 4 injectors plugged in on the 2nd-5th try relatively consistently. With the jumper engaged, the fuel pump is clearly audible (fuel pump new @ 2weeks prior to issues beginning).

I used the Clark's FUEL-16 procedure for the following -
DME Relay check - good
Confirm ignition switch voltage at DME relay plug (on fuse panel)- good
Confirmed voltage to the DME Computer plug - 18 &35 - good

I have replaced both the speed and reference sensors after attempting to confirm resistance caused the original plugs to disintegrate.

I confirmed spark with a spark tester.

I now have a fuel pressure test gage that I'll be installing this weekend.
I also ordered one of the F9 solid state DMEs with the LEDs to see if that helps. That should arrive today.

But, at present, neither DME will get it to start more than 1 time. The jumper will get it to start multiple times.
I'll provide an update this weekend - for sure on pressure check, and hopefully with a different DME.

[walfreyydo]

Originally Posted by JD1990

I have used the jumper. Currently I can get it to start with all 4 injectors plugged in on the 2nd-5th try relatively consistently. With the jumper engaged, the fuel pump is clearly audible (fuel pump new @ 2weeks prior to issues beginning).

I used the Clark's FUEL-16 procedure for the following -
DME Relay check - good
Confirm ignition switch voltage at DME relay plug (on fuse panel)- good
Confirmed voltage to the DME Computer plug - 18 &35 - good

I have replaced both the speed and reference sensors after attempting to confirm resistance caused the original plugs to disintegrate.

I confirmed spark with a spark tester.

I now have a fuel pressure test gage that I'll be installing this weekend.
I also ordered one of the F9 solid state DMEs with the LEDs to see if that helps. That should arrive today.

But, at present, neither DME will get it to start more than 1 time. The jumper will get it to start multiple times.
I'll provide an update this weekend - for sure on pressure check, and hopefully with a different DME.

A bad DME is really kind of the last resort option once youve gone through anything else, regardless sounds like thats not the issue as youve already tested with a known working DME.

The fuel pressure test will hopefully reveal some data. The fact that the car starts easier (but not perfectly) with the jumper in place is interesting and perhaps points to multiple issues. One of them potentially the DME relay, so its good you are getting the F9tech relay. I have one and they are apparently 100x more reliable than analog. It will never be an issue again (hopefully), assuming thats one of the issues.

A couple other things to check (apologies if this has already been mentioned):
-DME temp sensor
-AFM barn door voltage test
-Fuel Pressure Regulator (this will be revealed during the fuel pressure check if too high)
-Fuel Pump Check Valve
-Fuel Filter or fuel tank strainer clogged (this would show up as a drop in fuel pressure during cranking/running as the fuel cant push past the filters quickly enough to sustain pressure)
-Injectors clogged
-TPS (does it click when you first open the throttle?)
-IACV (should snap open/shut cleanly with 12V, if its sluggish or only open/closes partially it need to be cleaned)

All of these are related to fueling and air/fuel balance, especially during startup, which requires a richer mixture than when running. The DME needs to know when the engine is cold (DME temp sensor) and at idle (TPS switch). It also need to measure the amount of air coming into the engine (AFM) and have the correct amount of air bypassing the throttle plate (IACV). And of course needs the appropriate amount of fuel to balance those (injectors, fuel filter, pump check valve).

[djnolan]

The clarks reference is only so useful as it is for a 85.5 or later car. here is the wiring diagrams for 83 and up, should you need it, e.g. the dme relay is not getting the correct signals... I have never had to chase down this angle, and I am only familiar with the 85.5 and later cars. I don't know if the pin numbers are even the same?

https://web.archive.org/web/20070314120555/http://cannell.co.uk/944_workshop_Manual/Vol4-electrical.pdf

[JD1990]

2nd try at posting. Apparently the forum doesn't like me...
Weekend update.

I did receive the new F9 DME Relay on Friday. We installed and it fired off on 2nd try. I has a fuel prime component in the solid sate logic, so the fuel pump was easily noticed when I put the ignition to Run (prior to start). I was able to get it to restart with the new DME, however, it still took a couple of tries. And it seems that it will either start in the first few seconds, or not. Prolonged use of starter didn't help it kick over.

Observation -
the red - Fuel Injector led - was "on" when I plugged it in, and remains on after the ignition is turned off.
the green - Ctl Fuel Pump led - turned off after start when at idle. But the Blue Fuel Pump led remained on.

As for the other tests -
1. Fuel Pressure - I need to find a connector for the fuel pressure gage I have. Any suggestions are appreciated. I'm not sure I'm up to the task mentioned in the Clarks procedures.
2. Suggested items to check:
-DME temp sensor - added to list. I see the procedure.
-AFM barn door voltage test - added to list. (We have noticed a rich condition in the exhaust at start...)
-Fuel Pressure Regulator (this will be revealed during the fuel pressure check if too high) - noted for when I can gage hooked up.
-Fuel Pump Check Valve - recently replaced with the fuel pump.
-Fuel Filter or fuel tank strainer clogged (this would show up as a drop in fuel pressure during cranking/running as the fuel cant push past the filters quickly enough to sustain pressure) - Fuel tank strainer was just replaced at same time as fuel pump. I have a replacement fuel filter available and am going to change that out.
-Injectors clogged - just cleaned the injectors and replaced the consumables - O-rings, spacers, and injector screens.
-TPS (does it click when you first open the throttle?) - will check
-IACV (should snap open/shut cleanly with 12V, if its sluggish or only open/closes partially it need to be cleaned) - will check

Thanks all for the additional guidance and reference info (electrical diagrams).

[JD1990]

One other note - with it started, we did take her for a couple of runs. No hesitation was noted as we drove around.

[walfreyydo]

Originally Posted by JD1990

1. Fuel Pressure - I need to find a connector for the fuel pressure gage I have. Any suggestions are appreciated. I'm not sure I'm up to the task mentioned in the Clarks procedures.

You need to get an adapter from M16 to whatever the thread size is on the pressure gauge