Topic: EFI Cuts Fuel Intermittently, Anyone Seen This? Anyone Heard of This?

My 1983 Datsun 280zx straight six non-turbo has an EFI that is acting up.  Idle is fine, WOT is fine, but between 2000 and 4000 rpm the ECU is cutting the fuel off in short, repetitive pulses.  I'm going through "EFI diagnostic hell" now, checking AFM, TPS, wiring, etc. etc., but has anyone any idea what might cause such a thing? 

I caught this on video, at no load, 2000 rpm, AFT spikes repeatedly to infinity, which means ECU is cutting off fuel?
https://photos.google.com/share/AF1QipP … VDV3RvU1B3

Re: EFI Cuts Fuel Intermittently, Anyone Seen This? Anyone Heard of This?

I ran into something similar years ago, except WOT broke down also.  The ground wire to the fuel injector harness had broken about 10 inches away from the injectors in the harness.  Just the engine vibration running allowed the wires to separate just enough to break contact.  I had to take the injector harness apart and check each splice, and there are a bunch!  Check all grounds and run new grounds if necessary.

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Re: EFI Cuts Fuel Intermittently, Anyone Seen This? Anyone Heard of This?

It is also possible to see a "lean" AFR when the mixture fails to burn, like due to an ignition misfire.  Because the oxygen is still there.

Re: EFI Cuts Fuel Intermittently, Anyone Seen This? Anyone Heard of This?

Is it having a hard time reading your crank angle or cam angle sensor?  If it fails to read your sensor most ECUs won't know when to spark or fuel.

Are the lines to the sensor properly shielded.  If it's an aftermarket ECU do you have an appropriate pull up resistor if required?

Re: EFI Cuts Fuel Intermittently, Anyone Seen This? Anyone Heard of This?

This particular car has no crank angle or cam angle sensor.  The ecu reads pulses from the coil instead.  That wiring between the coil and the ecu is very suspect right now.  I'm going to pull the efi wiring harness and go through it, I also have another one I will swap out just to see.  The ecu is original to the car, I also already swapped it with another, with no effect.  Will let you guys know ...

Re: EFI Cuts Fuel Intermittently, Anyone Seen This? Anyone Heard of This?

I’ve had a problem with an engine randomly cutting out and it turned out to be broken solder joints on the drivers for the fuel injectors.

Going over the ECU with a soldering iron and some leaded solder resolved the issue.

Re: EFI Cuts Fuel Intermittently, Anyone Seen This? Anyone Heard of This?

Carburetors don't need a computer to run.

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Re: EFI Cuts Fuel Intermittently, Anyone Seen This? Anyone Heard of This?

How are the pulses generated? Is it reading the actual coil or something in the distributor?

In the daytona we had there was a hall effect sensor inside the distributor that did timing for the ECU. We had a problem with it breaking up that turned out to be the physical metal wheel coming loose from the rotor causing a messy signal. Don't know your setup, but if there are mechanical components give them a quick check.

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Re: EFI Cuts Fuel Intermittently, Anyone Seen This? Anyone Heard of This?

TheEngineer wrote:

How are the pulses generated? Is it reading the actual coil or something in the distributor?

In the daytona we had there was a hall effect sensor inside the distributor that did timing for the ECU. We had a problem with it breaking up that turned out to be the physical metal wheel coming loose from the rotor causing a messy signal. Don't know your setup, but if there are mechanical components give them a quick check.

I had a similar issue in an 88 Ram Charger. I dropped a new distrib in and problem solved.

"get up and get your grandma outta here"

Re: EFI Cuts Fuel Intermittently, Anyone Seen This? Anyone Heard of This?

I swapped the ecu, no effect.  However, both ecu's are old, I will open them up and check out the solder connections.

Yes, I have been thinking of carberetors lately.  When you have to get an oscilliscope to work on your car, it's too damn complicated.

As far as I know so far, the ecu gets spark timing and engine rpm from reading the coil negative lead only.  I need to to more research on that though.

Re: EFI Cuts Fuel Intermittently, Anyone Seen This? Anyone Heard of This?

fishchoke wrote:

As far as I know so far, the ecu gets spark timing and engine rpm from reading the coil negative lead only.  I need to to more research on that though.

Not trying to argue, but how does the coil know when to spark or the injectors know when to squirt without knowing where the engine is in it's cycle?  I don't think an '83 has mechanical ignition.

There is a crank angle sensor part for a 83 z-car.

Re: EFI Cuts Fuel Intermittently, Anyone Seen This? Anyone Heard of This?

rb92673 wrote:
fishchoke wrote:

As far as I know so far, the ecu gets spark timing and engine rpm from reading the coil negative lead only.  I need to to more research on that though.

Not trying to argue, but how does the coil know when to spark or the injectors know when to squirt without knowing where the engine is in it's cycle?  I don't think an '83 has mechanical ignition.

I think what he is implying is the hall effects sensor in the dizzy does not DIRECTLY feed the ECU ala the Bosch EZK ignition system where it feeds an ignition amplifier/ignition computer and then the coil negative feeds the ECU.  If that is the case, it is an odd system for sure because the (common) Bosch system normally had a feed off the ignition amplifier to the ECU on all the Eurotrash stuff but not sure on the Chrysler stuff (when it was used there).

Re: EFI Cuts Fuel Intermittently, Anyone Seen This? Anyone Heard of This?

OnkelUdo wrote:
rb92673 wrote:
fishchoke wrote:

As far as I know so far, the ecu gets spark timing and engine rpm from reading the coil negative lead only.  I need to to more research on that though.

Not trying to argue, but how does the coil know when to spark or the injectors know when to squirt without knowing where the engine is in it's cycle?  I don't think an '83 has mechanical ignition.

I think what he is implying is the hall effects sensor in the dizzy does not DIRECTLY feed the ECU ala the Bosch EZK ignition system where it feeds an ignition amplifier/ignition computer and then the coil negative feeds the ECU.  If that is the case, it is an odd system for sure because the (common) Bosch system normally had a feed off the ignition amplifier to the ECU on all the Eurotrash stuff but not sure on the Chrysler stuff (when it was used there).

My knowledge of this stuff is limited to what I have learned fixing the Bosch stuff on my own crapcan then converting to Megasquirt.