Otto Mechanic

I'm wrestling with yet another "no start" problem on my '89 S2. I'm using the Trouble Shooting guide at Clark's garage to work through the diagnosis, but I'm unclear on one point made there, which reads:

"For the fuel pump to start and remain running, for the ignition coil to develop secondary voltage, and for the injectors to fire, the DME computer must see an engine start signal or an engine running signal (greater than 200 RPM). When it does, it completes the circuit for the Fuel Pump / DME Relay secondary coil and the fuel pump starts."

My problem is the fuel pump. When the DME/Pump Relay is jumpered on pins 30 and 87b, the pump starts, eliminating the pump itself as a problem. Similarly, a noid light on an injector shows I'm getting injector signals from the DME. A "test plug" indicates I'm getting spark. But I'm not getting fuel.

If I open the intake after the AFM and spray in ether, the engine starts.

I've replaced the DME Relay using three different brand new (1 URO, 2 OE) relays with no change.

My question is; given that I have spark and an injector signal, can I rule out a DME and Reference Sensor failure? And if so, what's left?

Otto Mechanic

PS:

I've also performed the "alarm reset procedure for the S2" outlined here.

It may be worth noting that I've recently (since the last time the car was started) done work on the driver's side door lock mechanism to replace a broken link. Since that repair was made I can't unlock the driver's door with a key, but I can still unlock it using a key on the passenger side. I'll need to open the driver's side mechanism up again to re-connect one of the two plastic actuators that must have come unhooked.

jderimig

Are you getting fuel pressure at the rail when the fuel pump is running?

Otto Mechanic

I wish I could categorically say "yes" to that one, but I can't. My pressure gauge doesn't fit the S2 fuel rail so I'm still waiting for plumbing parts from eBay that I can use to build a 90 degree coupler for it, they should be here in a few days.

But I don't think that matters since I know the pump isn't delivering fuel at all unless the DME relay pins 30 and 87b are jumpered. I think trying three different relays of different manufacture ought to rule the relay out.

The real question is: if the Reference Sensor had failed, or the DME itself had failed, could I still get spark and injector signals? Clark's is vague on that point.

jderimig

Oh, ok didn't catch the point where the fuel pump wasn't running. On my 84 when I had bad reference sensors I didn't get spark, I don't remember if I got fuel. I don't which one was bad I changed them both and it got the engine running.

Does your tach bounce when turning the engine?

Otto Mechanic

Yes, I get a solid Tach bounce, and as I mention, if I inject ether into the intake the engine starts right up.

Otto Mechanic

PS: It's very helpful to know that when you had a bad reference sensor, you didn't get spark. That allows me to rule out the reference sensor.

jderimig

I am not the most experience 944 wrench here but I suspect your sensors a good.

I would still suspect the alarm system, I think there is a way to bypass the alarm system with a jumper arrangement on the DME. I might try and search that as I have no experience there.

jderimig

Caveat: I am going by memory 6 years ago.....

Otto Mechanic

I may have inadvertently found my problem.

I decided to use the DME relay bypass test described here.

The car didn't start, but when I got out of the cabin there was a strong smell of gas in the shop. I looked around and found a big puddle of gas under the tank just about where the fuel filter is.

I did replace the fuel filter while I was working on the suspension, a WYIT sort of thing. I triple checked the filter to make sure the arrow was pointing the right direction, towards the line that supplies the engine, but apparently the filter is blocking flow and when the pump is forced on it leaks like a big dog.

I don't know what's wrong with the filter installation, but I'm pretty sure now I know where the problem is. I have to say that a large puddle of gas in the shop on a 90 degree day was an exciting discovery. After getting a fire extinguisher and hosing the whole floor down without incident I feel a little better. Hands are still shaking a bit but a solid knock of decent scotch should fix that.

More later after I calm down a bit.

Otto Mechanic

I have that procedure, it's here.

But now I don't think the alarm is the problem. I've bypassed the fuel pump relay and that was a near disaster (see earlier post). That was a seriously bad idea. Now I get to repaint my shop floor. At least I didn't blow up my house.

jpk

The blocked fuel filter will not cause the pump not to run. The alarm should cut all power to the DME, so if that were the problem, you wouldn't get tach bounce or spark.
You could still be looking at a DME problem. Internally, there is a transistor that acts like a switch to send the signal to the DME relay to send power to the pump. If that transistor is bad, then no fuel pump. Might consider sending the DME out for repair.

PaulD_944S2

Scott, here's a suggestion from my experience.

Check and clean the wire lugs on the battery posts. They get a little corroded and then no current gets through. Don't ask how I know.

If it's not the problem, I'm sorry, but you have prevented a future failure.

Also, chances are if you are getting tach bounce, the DME is good.

BTW, I'm not too far away, in Riverside. We may have to meet up!

Otto Mechanic

I don't really know the pump isn't running when I try starting the car because the starter makes so much noise it would drown out the pump and I don't yet have a working fuel pressure gauge. I've been smelling gas during earlier tests though, I just didn't know where it was coming from until now.

After I check the filter installation I'll have no choice but to send out the DME. If I knew which transistor to check I could, at the very least, check the solder joints. I haven't tested a transistor in 40 years, can't even remember how and I don't have an oscilloscope anyway so I'll need to send it out.

Thanks,

Otto Mechanic

Hey Paul -

I just got a fresh can of DeOxit and I'm going through all the contacts now, but I'm getting enough to run the starter and the fuel pump so I don't have a lot of hope there. As soon as the shop floor is dry I'm taking out the filter for inspection.


Yeah, that would be great. I'm not in Paso yet, still selling my place in Santa Cruz. As soon as this car is running I'm moving the shop down there and I'll only be up here when I need to show the place. Planning to join the Central Cal PCA and start meeting the folks down there. I'll look forward to seeing you. Do you ever get to Buttonwillow?