JD928_S4

Hey all,
I have a 1989 928 S4 with an A/T. The other day I drove over to a friends house to hang out and when I got in my car to leave it would not start. I just would crank and crank with no signs of even a single fire. Before this the car was running fine. I proceeded to tow it back to my house and poke around under the hood. I have what seems to be a very nice spark at all the cylinders and the plugs are wet when i pull them. There is pleanty of fuel to the fuel rails as I have pulled the lines apart. I have compression and the sparking seems to proceed at a reasonable firing order. The wires and cap are fine. I am simply dumbfounded as to what the problem is, especially because the engine will not even pop at all. I halve alsoe checked all the fuses and inspeced both the EZK relay and the LH relay and they both appear to be fine. Anyway back to the garage to ponder some more. Thanks for any advice in advance.
Jacob Duffney

Imo000

Try jumping the fuel injection relay.

fbarnhill

I hate to be the one who mentions it but check the timing belt.

FlyingDog

Check the timing belt, then double check that you have spark and fuel. If timing, spark, and fuel check out fine, it's an injection issue. If you have spark, you have crank signal which goes to the EZK (ignition computer) which feeds it to the LH (injection computer). The LH batch fires all 8 injectors by grounding them. With the ignition off, check for continuity between the two pins on an injector connector. With the ignition on (fuel pump running), check for 12V on one pin (and only one pin). Let us know what you find.

Lorenfb

"With the ignition off, check for continuity between the two pins on an injector connector. With the ignition on (fuel pump running), check for 12V on one pin (and only one pin)." - FlyingDog -

When checking for 12 volts on the injectors, i.e. with just one injector plug removed,
both pins will have 12 volts since the other injectors provide the return path for the
LH control line to the voltage source. Only with all the injectors disconnected, will
only one injector pin have 12 volts.

The simplest and key troubleshooting start point is ALWAYS to check for a spark,
especially on a 928 since the LH (fuel) is dependent on the spark ECU (EZK).
Once an ECU potential problem source is localized, then its voltage sources
are determined followed by its trigger signal/signals. Use the methodology
here ( www.systemsc.com/tshoot.htm ) as a guide.

Bill Ball

You report you have spark.
You report you have plenty of fuel in the rails.
You report you have wet plugs - I assume not wet with oil, but fuel.

Pull the spark plugs and let the cylinders air out for a couple of hours.

Remove the air filter and try starting the car with starter fluid squirted down the intake throat. If the car fires then you have established you have spark but there is a problem with fuel (despite the wet plugs). Do this only long enough to establish that the car will fire on starter fluid (a few seconds). If the car still fails to start on starter fluid, then spark is an issue. If the car runs on starter fluid, but not without it, find someone locally with an 87+ 928 and try your LH brain in their car. It's a bit of a pain to get out of your car, but easy to plug into their LH harness plug and test that way.

I did encounter one 928 recently that would not fire at all despite good spark and good fuel pressure. It turned out to have a short of the wires in one injector plug lead. Since all the injectors share a common ground, a short in one injector lead takes all of them out of operation. To establish whether the injectors are firing, it's best to have noid light. You could do the lead voltage test Loren and Flying Dog mention.

I encountered another 928 a while back that would only start and run with the throttle floored. In that case the MAF plug was the culprit. It can't hurt to unplug and reseat the MAF plug. This requires removal of the air filter base to get to the MAF plug. You might leave the MAF unplugged and see if the car will start. It doesn't sound like a MAF issue, but who knows.

BTW, do you hear any random activity out of the injectors with the ignition in the on position?

Oh, one other thing - you should check temp sensor II. It is on the driver side of the water bridge. Pull the plug. Each pin on the sensor should be tested with an ohm meter to ground. At 59 to 86F the resistance should be between 3.6 and 1.4Kohm (lower at higher temp). A short or break there can prevent the car from starting.

Lorenfb

Bill Ball has provided a very comprehensive troubleshooting outline.
If the engine still doesn't start based on his outline, then consider the
mechanical aspects as mentioned; e.g. timing belt or cam timing,
or low compression.

Note: Don't assume that any spark is an adequate spark; i.e. the spark should
jump 10-25mm from the coil wire (removed from the distributor) to the engine
block/heads. The spark at the plugs should jump 8-10mm.

John Speake

Bill's advice is very sound, but be careful squirting starter fluid into the intake via the MAF. Keep the fluid well away from the venturi that contains the hot wire and other sensors, or you can start a fire in the MAF when the burn off cycle occurs when the igntion switches off.

JD928_S4

Tested the Temp II sensor and it reads .667K ohms and its about 70 degrees outside, I could see this affecting the performance but not limiting its ability to run. thanks for the advice Ill get back with more info in a little while. BTW I am just outside of albany NY and was wondering if anyone local would be willing to help if I cannot figure this out myself. Thanks again
Jacob

Bill Ball

Actually, a bad temp II sensor can affect starting as you lose cold enrichment. That reading is telling either the EZK or LH it's over 140F. If there is a complete break (unplug the sensor), I know the car will not start.

NOTE: There are two pins - you test them separately versus ground. One feeds a signal to the LH and the other to the EZK. Does one have a more appopriate signal? If so, swap the leads and see if the car starts (idea is to get the better signal to the LH). You can only do this if the AMP plug is gone (often true), although you could jumper the plug to reverse the leads. I've never tried this before, but it seems to me it might work. I'm not sure if both sides of the sensor fail together or separately.

JD928_S4

hey I juist checked the temp II sesor with each side vs ground and it has no conductivity or essentially a resistance of infinty. Is there any way I can jump the plug to this sensor or would that no work because I would need to ground out each side of the plug?? Thanks again
Jacob

Bill Ball

OK, it's bad. That is your problem. You need to replace it.

JD928_S4

ON my way to the store now to pick up a new temp II sensor hopefull bill is right and that is all that it is...keeping my fingers crossed. But I must thank all of you for your insite and help. THank you very much!
Jacob Duffney

JD928_S4

The Temp II sensor on the driver side has been replaced with a new unit but the new unit does not have any change from the old sensor. The resistacne between the two tips is about 0 ohms and the residtance between each tip and the block is still infinity or no circuit at all. I cant see the possibility of having a faulty new sensor... Oh and when I jacked the car but to get underneath for furthewr inspection I found that the last 3 days worth of starting with no result has left me with about a half cup of gas that proceeded to pour out of a joint in the exaust... so I guess it was a good thing id hasnt fired recently becasue I suspect if it had my car would have become a flying vechicle momentarily untill if came back to the ground after an explosion. lol.
ANy help at all would be great!
Jacob

Bill Ball

Somebody help me and Jacob. Am I wrong about temp sensor II? Each pin to ground should be between 3.6K and 1.4K Ohms in temp range 59 to 86F. Definitely should not be open circuit.