williamhk

All,

My 928 s4 has no power to the fuel pump and no spark to the spark plug

I have renew fuel pump relay and renew LH system relay.

What can I do to check or fix this problem?

Any reply will be appreciated. Thanks a lot.

Hilton

Possible causes:

failed EZ-K relay (the one with the tester in it - but can be swapped with any type 253 relay as they're functionally the same)
failed EZ-K ECU
failed Crank Position Sensor

My memory says the LH fuel pump circuit only energizes when it receives an rpm signal from the EZ-K, which is sourced from the crank position sensor.

IMO - most likely cause:
crumbled harness connector on the Crank Position Sensor

However - do you have access to an oscilloscope?

Before you get into the expensive parts-swapping phase, swapping the relays and also putting an o'scope on the terminals for the rpm signal at the EZ-K and LH harnesses connector is a great way to check whats going on

williamhk

Can I check the CPS with a multitester? becuz I dont have a o'scope.
If ok, can you tell me how to use multitester to test CPS?

Hilton

Not really - its a hall effect sensor, so you can't check continuity/voltage on it with a DVM.

Did you start by swapping the EZ-K relay? swap it with the horn one (make sure horn works first ) and see if you get spark. Guessing you're in Hong Kong from your forum name? (i.e. access to another S4 to test your ECU in is tricky).

worf928

No spark with good EZK relay means dead CPS, both coil amps or coils dead, or dead EZK. EZK rarely fails. CPS has limited life. 1 in a million for both coil amps or coils to die at same time.

Replace the CPS if the EZK relay is good.

Wisconsin Joe

Quick and dirty Crank Sensor test:

Watch the tachometer when you crank the engine with the starter.

If it twitches, the crank sensor is working. If not, not.

williamhk

Thanks for all replies.
For secure, which cause(s) (dead CPS, both coil amps or coils dead, or dead EZK) will also trigger another problem of no power to fuel pump, besides no spark?

Mongo

Fuel pump will not push gas in the motor if the crank sensor is toast. This is to prevent hydrolocking the engine with too much fuel.

worf928

It's to ensure that in the event of an accident that a working fuel pump doesn't spew gas into the wreck.

worf928

No CPS signal tells the computer than the motor is not turning. Therefore the EZK will not signal the coil amps. Thus no spark.

Or, in other words, the EZK will not activate the coil amps unless it sees that the motor is turning.

williamhk

Thanks for replies.
Oh, I have been thinking it is the problem of hall sensor.
But, now I know it is the problem of cps
and I am curious that what is the use of hall sensor?

dr bob

The Hall sensor on the cam gear helps the controller know which revolution the crankshaft is on, so it can adapt ignition in specific cylinders when it detects knocking. A failed Hall sensor allows the engine to run OK but not full power. Timing is retarded some to protect all the cylinders all the time, but engine will still feel pretty normal.

Failed CPS is the most common cause of your symptom, but it can be other things like a loose power or ground for the EZK box. What did the tach do when you tried cranking on the starter? Tach depends on CPS, as does the EZK for ignition. Fuel injection gets the engine speed translated and relayed on by the EZK box. No tach points you to cps..

jtrygstad

I experienced pretty much the same symptoms on my 89 GT a few years back. I changed out all the relays, jumpered the fuel pump, etc.

In the end, it was a the ECU which is prone to failure - a well documented Bosch flaw. I was fortunate enough to trade it out with a spare ECU from Motorsport here in SLC which showed a failed ECU was the cause. Ended up installing the improved Speake-modified ECU which also cures the Bosch flaw.

M. Requin

Actually, you can check continuity pretty easily, resistance should be between .6 and 1.6 ohms, and with a good DVM/DMM you should be able to see voltage pulses at cranking speed, I think. Haven't tried it with a DMM but have checked it with a scope And the most useful test is on the harness side of the connector on the CPS , which is what usually fails, so that it is tested also. I'm not familiar with the EZF system, but on the EZK, this can be checked on pins 7 and 19 of the EZK plug, which is where you hook up a scope to check the CPS signal. Pages 28-56 and 57 of the WSM for reference.

worf928

Different problem. You're describing an LH (fuel computer) failure. The EZK computer controls spark and will turn on the LH computer only if the EZK sees pulses from the CPS that indicates a turning motor.

OP has no spark which points to issues before the LH computer.