kevin Dubois

as some of you may know my brother and were working on his '88 S, doing an engine swap to a '90 S2. now that i am done with classes for a while, i have some time to work on this. here is the problem: we have the engine installed completely. we have power running, and have tried starting it a number of times. we have spark, and the fuel pump is running. however, the injectors are not injecting any fuel, so the car will not start. i tried bridging the terminals on one of the injector plugs with a light to see if there was any current flowing when the car was starting, but nothing (my digital multimeter is broke). i think i will try and get the multimeter fixed so i can verify that there is no current flowing across the injector plugs. anywho, what potential problems could cause no injector pulsing? if it is the DME, i still have the '88 S DME sitting here, i was thinking i could plug that one in to check and see if it isn't the problem. is there any huge difference between the DME'S? will the '88 S SME work for 1 minute?

Dal Heger

Check the connections on the crank reference sensor at the back of the engine, the one that reads off the flywheel. Also might want to check that the sensor is properly spaced (0.5mm from the actual flywheel teeth). I'd check the wire connectors, most likely they are brittle and cracked, causing a bad connection or no connection. Without that signal the DME will not allow the car to start (can't get a reference signal as to WHEN to fire the injectors and the ignition spark).

Check the simple stuff first!

Dal.

kevin Dubois

i thought about that, and i will definitely check it again, but i read in a previous post that if you have spark, that means the reference sensor is working properly. obviously i don't know this for sure, and i will check it again. what is the way to check if it is working right?

SoCal Driver

Only one sensor on the 'S' type engines. So if you have spark then the sensor is working.

One of the things that happens only to the 'S' style DME's is a burn through on a grounding circuit inside the DME. Aparently due to poor grounding and then the attemped start of the car through jumping to another car or with a charger. This cut's the circuit to the injectors. Check to see if you have battery voltage at the injectors. If not then it could be this burn through or a broken wire in the injector harness.

Think there was a thread about this on Pellican. Will have to look it up.

SoCal Driver

Found the Pelican tread:

http://forums.pelicanparts.com/showt...hreadid=136257

kevin Dubois

ahh, that is what i will check tommorow morning. the car has been on a charger a number of times already as it keeps killing the battery trying to start it (and now we have a new battery). i will pop open the DME and check out the burn out point his little picture thing had.

THANKS SoCal!!!

Dal Heger

Plus the other sensor (Hall Effect), in the cam sprocket housing that gives you the spark..... The "S" cars have that sensor to tell the DME when to fire the spark/which fuel injector to fire - TDC, intake sensor.

S and S2/968 have this setup.

Dal.

MHT

there is a hall effect switch/sensor on the back of the cam gear, the ecu does not need to know which cyl is at TDC for spark as that is taken care of by the distributor, but it does need to know for fuel injector firing. That info comes from the cam sensor. Is it hooked up, is the interruptor ring on the back of the gear?

SoCal Driver

Sorry the injector timing and the spark all come off of the flywheel. When you look at the lobes on the flywheel you will find a one that is a bit different than the rest -- TDC timing. The DME sees the difference in the pulses being sent to it.

The hall effect on the cam is for the two knock sensors. The DME needs to know which cylinder is knocking so it can retard it's timing. If the hall effect or either of the two knock sensors fail the DME retards the timing by 6 degrees. Really trick system. Think the 951 has a knock sensor too.

kevin Dubois

ok, update: i have taken apart the DME, and didn't find and signs of the ground lead cracking.

next, i checked the voltage across the injector plugs, and there was no voltage at all (done with the key in the running position). i then checked the resistance from the injector plug to the DME pins 14 and 15 because i heard that those were the pins that control the injectors (if i'm wrong on this, please correct me). THere was no resistance (open loop) from either of the pins on the DME, to either of the two pins on the injector plug. i suspect there may be a second plug for the injectors that may not be connected somewhere. can anyone verify if there are any connecting plugs for the injectors?

also, using the shop manuals i noticed that there is a plug for the ballast resistors that runs the power to the injectors. where are the ballast resistors, and do they use a connector like the diagram shows (where is the connector)?

kevin Dubois

bump.

kevin Dubois

anyone?

Dal Heger

Sorry man, I have no idea. Maybe the DME is toast? If you checked and triple checked all the connections to the sensors, checked the wires for breaks, and made sure that everything is hooked up properly then that's the next thing to look at. You did check the condition of the crank reference sensor (condition and proper height above the flywheel) right?

For the S cars there is also an ignition module in the front driver's side headlight area. I don't remember if you said that you had spark or not. That module often fails. I'm not sure if it's only on the S2/968 though.

Did you have the fuel injectors cleaned while they were out? If so, unless they were run with gas after they were cleaned they are most likely gummed up solid and need to be cleaned again. If they were out for a long time (even without cleaning) then they might be gummed up with varnish from the fuel sitting in them for so long.

Just check the basics.

Dal.

Bryan

You need to look at the wiring diagram for the S2. Find the pins on the ECU that pulse the injectors and measure resistance across, say, injector pin 1 and the ground pin. Should match what you get across the pins of the injector itself. Then make sure there's zero resistance between the ECU's ground pins (there may be a couple of them) and the negative battery terminal.

Did you have to do any wiring changes to the car? When I did this conversion on my 8-valve 944, I had to rearrange the pins in the rectangular black plastic connector back by the brake booster. 14 pins I think? But this was to plumb in the igniter module for the ignition system. And I think this connector is just for the ignition system and perhaps the oil level sender as well.

I also had to add a constant 12V signal to the computer - which I think is only for fault code memory and you may have this since you're starting with an S.

I had to change the plug where the instrument harness connects to the ECU harness, but that's just to get the instruments working. Shouldn't keep the engine from starting.

What about grounds? There's a main ground from the negative battery terminal that goes onto the...errr....starter terminal? Or is it the one on the bellhousing? I forget. The starter won't turn without this hooked up. But there's also a ground for the ECU harness that connects to the bellhousing near the top. Make sure this ground is hooked up and clean.

Bryan