I have an ongoing problem with my 1983 280ZX Turbo.

When I'm idling or driving at a steady speed (engine RPM doesn't matter), every 5-10 seconds the car loses power - just like I lifted my foot off the gas. The engine speed drops off sharply as if I took my foot off the gas. As soon as I touch the gas pedal, the revs pick up and it runs fine - for another 5-10 seconds at steady throttle, then the engine revs drop again and the cycle repeats.

If I'm driving in traffic where I'm on and off the throttle, this does not occur - it only happens when I've been at a steady, unchanging throttle setting for a few seconds.

The tach stays active and shows the gradual decline in engine speed, so it's not the ignition cutting out. (And this is a turbo, so there's no ignition module to go bad.)

So - as soon as I press the gas pedal, the car immediately responds and accelerates. When I've been at steady speed for another 5-10 seconds, this happens all over again and the car loses power. It always responds and accelerates when I hit the gas pedal.

This happens whether the engine is cold or hot.

- ECU has been replaced and all connections coated with Deoxit to assure contact.
- Fuel filter has been replaced.
- Fuel pressure was been tested last summer after the problem appeared and was OK.
- Air flow meter has just been replaced with new AFM.
- Head temp sensor has been removed and tested - it passes.
- Cat converter has been checked for clogs (I removed it and sighted through it) and it's not plugged.

Other ideas are welcomed.



Edited 2 time(s). Last edit was february 07, 01:49pm.

I have no suggestions for you.
I just wanted to thank you for showing you've done a basic search by what you've written and thank you for giving as many details as you can about how to reproduce the condition.
It's always a treat to see that type of question.

Question from a co-worker. Has your turbo or gaskets to it been changed lately? He says it sounds like either a boost controller or the turbo itself is faulty and leaking slowly.

---

Edmonton, Alberta, Canada.
My main areas of knowledge involve the ZX.

Grammar Saves Lives! IE: Lets eat Grampa or Lets eat, Grampa.



Edited 1 time(s). Last edit was february 07, 02:02pm.

I have seen this exact same problem, so I can tell you with a high level of probability is the .... fuel pump modulator.

It is located above the ecu on the driver's side.

Bypass it and let us know if it fixes it.

*Edit* Forgot to add, a test for it is if when you drive the car, if you constantly vary the speed (throttle) slightly, does it stop the cycle and the problem goes away?

---

Blue 83zxt coupe .. Eibachs , Tokicos , GReddy stuff, B&M sts, Magnaflow
Orange 77 280z coupe ..

Seattle WA



Edited 1 time(s). Last edit was february 07, 05:35pm.

Turbos do have an ignition module/transistor O_o

Its on the same bracket as the ignition coil, provided we are thinking of the same thing.

Nope, thats the ignitor, its almost for sure the fuel pump modulator.
I reread the op, and it does pass the variable speed test, thats the giveaway.
Fooled me for awhile before I tracked it down.

---

Blue 83zxt coupe .. Eibachs , Tokicos , GReddy stuff, B&M sts, Magnaflow
Orange 77 280z coupe ..

Seattle WA

JPZX Wrote:
-------------------------------------------------------
> Nope, thats the ignitor

Yeah, but different people call it different things; ignition module, ignitor, power transistor (what the service manual calls it), just makin' sure he wasn't confusing it with something else.

Just sayin'

Fuel pump modulator does sound like a good bet though.

Good post. Weird symptoms that happen infrequently. I'll squirrel this away.

---

Chattanooga, TN
82 white w/ red n/a coupe 120,000 miles.
83 2+2 314,395 miles at college AGAIN
96 Pathfinder, 96 Maxima
90 300ZX 2+2, 82 ZXcoupe, 81 200sx, 72 Camaro SS, 68 Mustang, 1950 Chev PU fully restored
Pics:[www.zcar.com]

Danzeman Wrote:
-------------------------------------------------------
> JPZX Wrote:
> --------------------------------------------------
> -----
> > Nope, thats the ignitor
>
> Yeah, but different people call it different
> things; ignition module, ignitor, power transistor
> (what the service manual calls it), just makin'
> sure he wasn't confusing it with something else.
>
> Just sayin'
>
> Fuel pump modulator does sound like a good bet
> though.

ignitor is a fancy jap word for power transistor or ignition module lol

---

______________________________________________________________________________________________
83 Turbo 280ZX - NSX Manual Boost Controller set @ 12psi , Greddy Type-S Blow Off Valve, Faze Boost Gauge, Air Fuel Ratio Gauge, NGK BRP6ES Plugs, Short Ram Intake, Full 3" Apexi Turboback Exhaust, 3" Test Pipe, Tokico Rear HP Shocks, Walbro 255 Fuel Pump, MSD Blaster 2 Ignition Coil, Gripforce Stage II Clutch, BF Goodrich G-Force Sport Tires, Port Matched, Ceramic Coated, and Header Wrapped Turbo Manifold and Downpipe, CX Racing SR20 Aluminum Radiator, CX Racing Front Mount Intercooler, Port Matched Z31 Watercooled T3 Turbo

SR20 Radiator Swap [www.zcar.com]

-Chris M., Arlington, TX

I'd be DELIGHTED to check the fuel pump modulator. But wait...in the 19 years I've had this turbo, I've never heard of that part...so I checked the factory service manual.

On a turbo model, there is no part by that name. There is a fuel damper mounted near the fuel pump outside the fuel tank, and there is a fuel pressure regulator located on the fuel injection rail.

I'm familiar with the fuel pressure regulator and have changed it in the past, although it has been a few years (more than 3).

Neither of these are located above the ECU - in fact, there are no components I can identify in the fuel system located above the ECU on the turbo model; the ECU is inside the car behind the kick panel in the driver's side footwell...no gas running through there.

Could the damper or the regulator be the parts in question? The regulator is easy to reach and replace, and I'm sure the damper is manageable. It does make sense that it would be something in the fuel system, as the engine is clearly losing fuel but movement of the gas pedal restores it immediately.

According to the manual (p. EF & EC-49) the damper's purpose is to damp pulsations from the fuel pump, and the pressure regulator's purpose is to return surplus fuel to the fuel tank.

Logic tells me that pulses from the fuel pump would be unlikely to affect the car in the way I'm experiencing (and there's not much to fail in the damper), but it seems to me that a malfunctioning regulator might be returning too much fuel to the tank and letting the engine starve. Does that make sense?



Edited 1 time(s). Last edit was february 07, 09:02pm.

Pilgrim Wrote:
-------------------------------------------------------

> On a turbo model, there is no part by that name.

> Neither of these are located above the ECU - in
> fact, there are no components I can identify in
> the fuel system located above the ECU on the turbo
> model; the ECU is inside the car behind the kick
> panel in the driver's side footwell...no gas
> running through there.

Thats because its electrical dude.

Page 66 of EFEC.





Edited 1 time(s). Last edit was february 07, 09:31pm.

The fsm is defficient in a few areas of the turbo car, even the turbo supplement.
Its a fair sized box above the ecu.
What it does is change the voltage going to the pump depending on demand.
Seen it twice cause your exact problem.
Look harder. If I have time tomorrow after work I'll take a picture.

*Edit* Thanks danzeman, was writing when you posted above info...

---

Blue 83zxt coupe .. Eibachs , Tokicos , GReddy stuff, B&M sts, Magnaflow
Orange 77 280z coupe ..

Seattle WA



Edited 1 time(s). Last edit was february 07, 09:31pm.

Keeping the FPM in mind, I would also suggest that you examine the Throttle Position Switch (TPS) on the side of the throttle body. If it is broken, loose, contacts stuck, or just badly out of adjustment, it can send spurious IDLE signals to the CECU and the FPM, which could also cause the fuel pump's voltage to be lowered by the FPM, until wiggling the gas pedal caused a change in the signal, jumping the pump voltage back up to full.

Try disconnecting the wiring harness connector to the TPS, using a zip tie to secure it to one side, so it cannot touch anything. Then drive the car for a while, so see if the problem persists or goes away. If it goes away, the TPS or it's wiring is somehow responsible for your trouble.

If the TPS is working and adjusted, one way to test it is to let the car idle until warmed to normal temperature, then just tap the gas, and you should be able to hear the fuel pump speed up to full pressure for a few seconds, then drop back down to low pressure speed if there is no more gas pedal activity.

If it passes this test, that does not mean that the TPS or it's adjustment or cleanliness is not part of your problem, but it is something else easy to check.

---

Bob, in San Diego
1983 280ZX Turbo Coupe 5 speed

Visit [xenons130.com] for ZX Manuals, or
[www.xenons30.com] for 240Z, 260Z, or 280Z manuals.
Blue's Tech Tips [www.atlanticz.ca]
member Z Club of San Diego [www.zcsd.org]

*** Help stamp out "texting" abbreviations!!! ***

JPZX Wrote:
-------------------------------------------------------
> The fsm is defficient in a few areas of the turbo
> car, even the turbo supplement.
> Its a fair sized box above the ecu.
> What it does is change the voltage going to the
> pump depending on demand.

No KIDDING it's deficient if it doesn't identify this part. I'll check p. 66 when I get home tonight.

Thanks, guys! I will get on this as soon as we get a little snow melt. The car's under a cover in the driveway and I've been working on it as weather permits. We didn't get the snow dump here in Colorado that the east coast did, but we got a couple of inches yesterday and it's going to be below freezing most of the week.

And yes, if it happens that you can come up with a photo, that would be helpful.

I posted a pic of the location, unless it didn't load where you are currently at. >_>

Yes indeedy!

I see it now....and thank you VERY much!

Probably the first thing for me to do is pull out the Deoxit and go over the electrical contacts. I'll also check the FSM to see if there's a way to test it.

If no joy, then I'll go on the hunt for one.

Update: I think I just found a thread on zdriver.com that deals with this exact problem - and even gives me a way to test it by grounding the wire that sends a signal to the relay and thereby keeps the pump on while the ignition is on. That's not safe to do on an ongoing basis, but a very handy way to conduct a test.

[www.zdriver.com]



Edited 2 time(s). Last edit was february 08, 01:23pm.

Final discovery - it is the fuel pump control modulator. After reading the other thread, I went to the connector and found TWO white wires - but one was all white, the other was white with a yellow trace. I unplugged the connector and cleaned it with Deoxit on the off-chance that it was a bad connection - no luck. Then I stuck a jumper wire into the back of the connector on the solid white wire, re-connected the connector and grounded the other end of the jumper. I can hear the fuel pump run constantly and the car does not stumble or die. The fact that it continues to run seems to prove a bad modulator.

The modulator is in a rather difficult place to reach - but I'll order one and change it out. Until it arrives I'll leave the jumper in place, let the fuel pump run when the key is on and the fuel system will return the excess fuel to the tank. Not ideal, but it will only go on for a few days and on short trips.

Glad you found your problem.

Make sure the vacuum hose to the FPR is good. That will ensure that the fuel pressure is lowered in the rail at idle and low RPMs. With the pump running at full speed all the time, the car might run a little rich at idle, but you might not even notice.

Since the FPM runs the pump to high flow just about any time you are moving faster than a walking pace, I would say drive it as far and as fast as you like, just avoid rush hour stop & go traffic, and such. It should be fine.

If your fuel hoses are factory original, you might take the opportunity to inspect them for damp spots, caused by the slightly higher than normal pressures. If, after a drive, you see any damp spots on the fuel lines, or slight weeping, buy new high pressure EFI fuel line, new EFI hose clamps, and replace them. At night, use a high power flashlight to inspect the fuel lines and the injectors, fuel rail, and FPR, to see if you can see anything odd, like little wisps of vapor, or little jets of stuff. Those can happen on any engine with old hoses, but will somewhat higher pressures, while you wait for your new modulator, you might want to check yours, just to be sure.

---

Bob, in San Diego
1983 280ZX Turbo Coupe 5 speed

Visit [xenons130.com] for ZX Manuals, or
[www.xenons30.com] for 240Z, 260Z, or 280Z manuals.
Blue's Tech Tips [www.atlanticz.ca]
member Z Club of San Diego [www.zcsd.org]

*** Help stamp out "texting" abbreviations!!! ***

Good thoughts. Some of the hoses are old, some have been replaced. Good opportunity to take stock of their status!