Missing Cylinder #2

SolReaver · 11-22-2006, 12:30 PM

The project (87 924s, 2.5L) car has taken to running roughly and it doesn't have the porsche-esqe power I expect from such fine german engineering.

It sounded and felt like a missing cylinder. Upon pulling the plug wires from the cap one at a time I noticed that there was a big difference in pulling wires 1,3, and 4. Upon pulling the #2 plug wire there was little or no difference. Taking the easy way out I replaced the plugs. still number 2 cylinder was no where to be seen. Later I will try replacing the plug wire with whatever I can get from a parts bin to rule out the wire.

I am suspecting a fuel injector or some sort of injector signal as the exhaust is not particularly gassy and the plug removed was not particularly wet or washed.

I do not yet have a manual (in the mail) so I am asking:

How Do I check the fuel injector? where does the signal wire travel to and from? Is there one of those little test lights that can hook up to the injector connection? (it blinks on signal)

Any other suggestions would be appreciated.

I may check the compression if I can get a tester.

SolReaver · 11-22-2006, 03:48 PM

P.S. The little light that plugs into the injector where the injector goes is called a "Noid" available where all fine tools are sold.

SoCal Driver · SoCal Driver's Garage

Check the compression.

SolReaver · 11-22-2006, 06:55 PM

Checked compression, 150,150, 145, 145 all good!
I switched the 2 and 3 wires at both ends, still missing cyl #2.

Compression good, ignition good, I am thinking fuel. How does one test that? Is there a hall sender on this model? where?

The other Cylinders are running champion, what is 2's problem? What makes it so differnt and special?

I now have 2 manuals, however neither covers the 2.5 L engine.

SolReaver · 11-22-2006, 07:17 PM

I had the plugs out for the compression test, I put the plug in the 2 wire and spun the engine, Spark, Spark, Spark.

Razorback1980 · Razorback1980's Garage

If the voltage to the injector tests fine, then I would pull the injector out and put a clear plastic hose on it and run the hose to a can on the floor. I can then watch how the injector sprays the fuel...if it does at all.

SolReaver · 11-26-2006, 04:02 PM

Still waiting on the noid. Trying to borrow a voltometer. I got a stethescope from a friend and listened to the injectors. 1,3 and 4 all tick, tick, tick. 2 is silent. I hit the fuel rail with some spray to prep everything. I will open it up if I find there is signal going to the #2.

SoCal Driver · SoCal Driver's Garage

Bad connector. Pull the rubber boot back and see if any of the wires are pulled off the pins.

SolReaver · 11-28-2006, 10:32 AM

going over to the car later today. I will check pins and connections. I spoke to the guy at Witch hunter. He said it sems like a stuck injector. Not surprising as the car sat for so long. I drained the old fuel and put in new stuff before firing it up. Oh well. FYI he reccomends testing the injector as folows: Hook up a pressure guage to the fuel rail and use a little 9v to trigger the injector, pressure drop and it is working. I don't have a presure guage so I am just going to remove the plug and listen for a hiss or click at the injector with the stethescope. Again, the noid is in the mail (still) and I will use that or a voltmeter to test for signal to the injector. If the injector is stuck, I can try rapping on it lightly with a hammer to un stick it. If that doesn't work, I will send the 4 of them out to be serviced. The car has 100K or more on it and I am pretty sure they are the original injectors. Probably a good idea to have them all done and flow matched. I think they should be serviced or replaced every 60 to 80K which means they are overdue anyway.

hpaulb · 11-28-2006, 11:28 AM

Easier than you think. Pull the rail out of the intake manifold. Leave in the rail. (4 bolts) Stick them in 4 glass botles and watch as somone turns it over. Maybe remove the coil wire first. You should see a fine spray and evenly fill the jars. It is hard to deturmine trigger pulse from a meter. Use an osiliscope.

SolReaver · 11-28-2006, 03:36 PM

I pulled the fuel rail. Yes, pretty easy(4 10mm bolts and a little wiggling) Upon cranking the engine, 1 AND 2 are not squirting, 3 and 4 are squirting fine.

I put 1 and 2 leads on injectors 3 and 4 and got no squirting. I put the 3 lead on injector 2 and it worked fine. I did the 9volt battery test to the injector connections after pressurizing the manifold and got all 4 injectors to squirt fine.
The connections look good, I will peel back the boots tomorrow and check there. So far it looks good with no major corrosion.

So, it seems I am not getting SIGNAL to 1 and 2.
The injectors appear to be fine.
When I began this project, I could have sworn the #1 cylinder was functioning at least a bit, which leads me to believe this puppy is dying on the table.

W...T....F...???

Riddle me this Batman: do injectors 1 and 2 share a common ground or something? Before I go tearing apart the harness to look for a short is there another likely suspect I should be interrogating? Where do the injector leads go what gives them signal? Unfortunately, I do not have an oscilliscope.

Fedex tells me that the manual is almost here. I have a feeling this may be beyond most troubleshooting flow charts.

I would do more today, but I would like to think out my next move and the gas fumes were giving me a headache.

Any input would be welcome at this point. Thanks for looking.

SolReaver · 11-28-2006, 04:52 PM

Ah Ha! They Do have a common ground! both injectors ground to either 88e or 88b on something called the Fuel injection Combo Relay!

Pins 15 and 33 go to inj 1 and 2 respectively, pins 32 and 14 go to 3 and 4. 37 and 38 come from 1 and 2 connect up to 88e. Pins 40 and 41 come from 3 and 4 and connect to 88b.

Now If I only knew where the "fuel combo relay" was and what it looked like. I do know it is a printed circuit and prone to soldier failures. (hmmmm)

Sorry about the double posts folks, this is where I keep my notes.

Jump in anytime if you can help me out here.
I just got and looked at that poor excuse for a factory manual you folks are supposed to work out of and I am, well, less than impressed. the above info came off the net on a search for l Jetronic, lots o good stuff out there.

Thanks

SolReaver · 11-28-2006, 06:41 PM

Injectors 1 and 2 do not share a common ground, they share common power through the Fuel injection combo relay. the ground is through the control unit and I really am hoping that is not the problem. BTW, I have found out there are a bunch of cars that share the L-jetronic Fuel infestation system the 528i for example, ya learn something new every day.

SoCal Driver · SoCal Driver's Garage

Fuel Injection Combo Relay...

The what???

SolReaver · 11-28-2006, 09:02 PM

Dual Relay- it is the relay that powers the fuel injection and the fuel pump, I think it may power the ignition. I can't be sure as I only have engine sections of the 944 factory manual and cannot seem to find an exact wiring diagram at this time.

I am guessing it is referred to as a fuel pump relay or ignition relay or something along those lines.

Anybody have a good wiring diagram 4 this model? (see sig)

on a 912e the relay is part #923 615 101 00.

In any event this relay has several pins, two of them should be labeled labeled 88b and 88e, these pins go to Injectors 3 and 4 and injectors 1 and 2 respectively. I am thinking that there is either no power or a bad connection somewhere between 88e and injectors 1 and 2, thus both are not getting signal. This is only a theory, but it makes sence as to why 2 injectors are not geting signal and the other 2 are.

I will check for power at the 88e pin and continuity between that pin and the injectors. That is, once I Locate this relay. Any guesses as to what it is called and where it is?

hpaulb · 11-29-2006, 08:24 AM

OK here is the circuit path:

All injectors common point RT/BL color, connection SP3 and go to Fuel pump relay pin 87.

Injector 3&4 Gr color to SP2 connector, Gr to pin 14 of DME

Injector 1&2 GR/BL color to SP1 connector, change to GR/SW color to pin 15 of DME.

If 2 are firing, check the common anyway. I would think the the common to the DME for 1&2 are coroded or somthing.

SolReaver · 11-29-2006, 09:21 AM

Ok, Fuel Pump Relay, Pin 87 is where I start. (many thanks)
check Rt/Bl and SP3
checkGr/sw and Sp1 (suspicious)

Just an aside, the injectors are grounded individually via the DME
(generic L Jetronic pinout)
Inj 1 DME pin 15
Inj 2 DME 33
Inj 3 DME 32
Inj 4 DME 14

So I will (very carefully, after disconnecting the battery and waiting a bit) check the main ground to the unit. and clean the big connector.

I have encountered FI Digrams that are not accurate as to actual colors, so I will proceed skeptically, however, this a good start.

My research has shown some L jetronic systems may only trigger 1 of the banks on cranking and energize the rest on run. I do not know if this is the case. So if Anyone out there has cranked the engine with the fuel rail out, let me know if all of the injectors are supposed to fire. That way I am not chasing shadows. If there is a seperate circuit for the first bank going to the relay this may be the case. I'll let you know.

hpaulb · 11-29-2006, 10:18 AM

Acording to my shop manual for the 87 924S there paired. pin 14 or 15? Use an ohm meter to verify. The DME is an active low meaning it draws the line to ground. 12DC is constant on only off if the relay/ignition is off. To test firing, go down line, disconect the SP 1 conection and short to ground (not DME side to be safe).

SolReaver · 11-29-2006, 03:24 PM

OK, I went there:
Pulled the battery, Dropped the brain,and cleaned every connection, fuse, relay, ground and terminal I could get to. I didn't find anything really corroded, just the normal 20 year old tarnish. I found the fuel pump relay (it is the one with the red fuse on top of it) and Pin 87. From there on, I could just not follow it without removing the fuse/relay block and I didn't have enough time to do that as I wanted everything back together before I forgot where it all goes.

I checked the voltage with the ignition on at the injector connections and it is all 9v (both sides, each connector) the battery needs charging before I can test it further. All Injectors read 3 ohms, and all trigger (squirt) with the little 9v I use for testing.

HpaulB: your shop manual says they are paired. They are paired 1+2, and 3+4, Yes? Does the 1+2 pair go to the same pin 87 as the 3+4 pair? If so they are truly common and I might be able to just tap into the Inj 3 common to 1 and 2 in the injector harness above the rail. (if I haven't fixed it already) I am reading 9v at all injector pins (I think it is supposed to be 9v, not 12v) with respect to motor ground.

I will verify the DME injector connections if I have to go in there again. I really think each injector has it's own pin on the DME (CYL=Pin) 1=15, 2=33, 3=32, 4=14, otherwise, how would each know when to fire? Most of the time, the injector has 9v on both sides, so to the injector there is no voltage across the pins. The DME sets the pin to ground and the 9v common feed goes to that ground through the injector, triggering off the injector. (voltage across injector pins= squirt)

As this is important, Which one is SP1? where is it, and what does it look like? (I probably cleaned it already) Thanks for your help.

Nifty maual you have there, I will probably be needing one eventually.

SolReaver · 11-29-2006, 03:24 PM

OK, I went there:
Pulled the battery, Dropped the brain,and cleaned every connection, fuse, relay, ground and terminal I could get to. I didn't find anything really corroded, just the normal 20 year old tarnish. I found the fuel pump relay (it is the one with the red fuse on top of it) and Pin 87. From there on, I could just not follow it without removing the fuse/relay block and I didn't have enough time to do that as I wanted everything back together before I forgot where it all goes.

I checked the voltage with the ignition on at the injector connections and it is all 9v (both sides, each connector) the battery needs charging before I can test it further. All Injectors read 3 ohms, and all trigger (squirt) with the little 9v I use for testing.

HpaulB: your shop manual says they are paired. They are paired 1+2, and 3+4, Yes? Does the 1+2 pair go to the same pin 87 as the 3+4 pair? If so they are truly common and I might be able to just tap into the Inj 3 common to 1 and 2 in the injector harness above the rail. (if I haven't fixed it already) I am reading 9v at all injector pins (I think it is supposed to be 9v, not 12v) with respect to motor ground.

I will verify the DME injector connections if I have to go in there again. I really think each injector has it's own pin on the DME (CYL=Pin) 1=15, 2=33, 3=32, 4=14, otherwise, how would each know when to fire? Most of the time, the injector has 9v on both sides, so to the injector there is no voltage across the pins. The DME sets the pin to ground and the 9v common feed goes to that ground through the injector, triggering off the injector. (voltage across injector pins= squirt)

As this is important, Which one is SP1? where is it, and what does it look like? (I probably cleaned it already) Thanks for your help.

Nifty maual you have there, I will probably be needing one eventually.