‘91 300zx TT no start no-spark no-fuel pump

Post by **Larry60** » Sun Jan 05, 2020 5:05 pm

My 300ZX tt has not stated for long time. Other distractions keeping me from looking at it. Until now.

Starter spins engine fine but not a sign of starting. Fuel pump not running. No spark.
Code 55 so ok. ICM contacts green so cleaned with alcohol and small brush.

No change

Tried a number of things but can’t get even one sound of firing, even from one cylinder.

Would a bad ignition control module stop the fuel pump as well as spark?

Post by **Larry60** » Sun Jan 05, 2020 7:37 pm

I guess it’s called a Module - ICM.

Post by **Larry60** » Mon Jan 06, 2020 6:58 pm

Fuel pump now working. Not sure why.
Pulled & rotates cps to check injectors. Six injectors clicking. Checked pump relay, it was clicking. Then pump started working. Had to turn motor over to get good pressure at output of fuel filter. Need to check fuel pressure regulator.

Still Not starting. No single cylinder firing.
Need to track down no spark.

Ignition relay and fuses are ok.
What else can stop spark?

Post by **Larry60** » Tue Jan 07, 2020 3:52 pm

Spent some more time cleaning contacts on ICM / ICeU. Still no fire/spark.

But now getting a 21 ECU code. Also the tack is not moving at all while cracking.

I’m guessing ICU is fried.

Any suggestions to conf that, before I spend $$$ on replacement?

Post by **itsa300zx** » Wed Jan 08, 2020 10:58 am

Test the ICM (also called power transistor unit PTU) as shown in the FSM.
My suspicion might be the sub harness.

PTU looks like this:

Post by **Larry60** » Wed Jan 08, 2020 2:48 pm

Thanks for the "Trouble Diagnoses" page but i have some questions..

My ICM/PTU has an extra cable around the box to the car harness. Is that the "sub-harness" you talked about?
Since the connector keys at the car end of the "Sub-harness" match the picture in the trouble diagnoses, I tried to ohm from the car end of the sub-harness.
First, is that correct or should I go straight to the ICM connectors? (ICM Connectors don't look like drawing.)

I used the drawing and the sob-harness connector keys to identify "g" .. "a" and 1 ... 6 - Not marked on connectors.

I'm getting the opposite readings of open and 2M+ on the "g to "a" b c d e and "f" from the table.

Also, getting opposite for "a" to "1" and "b" to "2" and so no.

Just thinking it odd that all are exactly opposite on every pin.

Is this telling me the ICM is bad or am I just confused?????

Post by **itsa300zx** » Wed Jan 08, 2020 3:07 pm

Yes that wire bundle with 2 grey and 2 black connector is the sub harness. Its purpose is to adapt to the "newer" S2 PTU, as shown in my second picture, top smaller black box.

Test the PTU with it removed from the car. Side with 7 pins is a-G and 6 pins are 1-6

By the sounds of it the ptu is shot. Doulbe check you have the + and - probed correctly.

Post by **Larry60** » Wed Jan 08, 2020 4:13 pm

Thanks, probes polarity correct. Even went to the pins on the PTU, got same results. (Back traced the sub-harness)
Still odd that all are exactly opposite polarity.

Should I be testing all the coils also, to be sure that's not blowing out the PTU?

Is there a source for a tested but used PTU? (Just to get this question resolved.)

Post by **itsa300zx** » Thu Jan 09, 2020 9:58 am

Testing the pack is also a good idea.
Sorry I dont have a source for use ptu's. Maybe post in a want ads in various 300zx forums.
Should also try to figure out why the ptu failed so your new one doesn't do the same, ie a short some where in the wiring.

edit:
ebay has some used PTU, seller spoolinenterprise (AKA zhookup out of Missouri) I've purchased many Z32 items from them.

Post by **Larry60** » Thu Jan 16, 2020 3:13 pm

Not the ICM.
Sprayed cleaning fluid into intake. Stared for couple seconds. So spark is good, now.

Fuel pump running while cranking. Fuel thru filter, thru injector rail and out return to gas tank. Not sure if pressure is enough.

Injectors click when turning Cam Position Sensor. Likely clogged injectors or inadequate fuel pressure. ?????

What should fuel pressure be?

And is there a way to clean injectors in place? (Don’t want to pull intake to get to them.) odd that all injectors stopped working at same time????

Post by **itsa300zx** » Thu Jan 16, 2020 5:09 pm

You say car had been sitting for a long time? How old is the fuel? Nominal fuel pressure should be anywhere between mid 30's to mid 40 psi.

Post by **Larry60** » Thu Jan 16, 2020 11:02 pm

Yes, fuel is old. Very low old gas. Added new.
Also substituted external tank & pump. With new gas.

Found more nuisance things since. Car now starts but will not keep running.

Looking at other connectors (MAF, temp.).
Vacuum leaks?
Don’t have good fuel pressure gauge.

Any suggestions on keeping it running?

Post by **Larry60** » Thu Jan 16, 2020 11:03 pm

BTW - New fuel filter.

Post by **Larry60** » Thu Jan 16, 2020 11:07 pm

Interesting observation:
Fuel pump runs briefly when key first turned to run. But no pressure thru filter.

Is that normal?

It does run while cranking.

Post by **Larry60** » Thu Jan 16, 2020 11:19 pm

I put vacuum on Fuel Pressure Regulator Valve. It held vacuum. May have been clogged, since it started soon after. (But only tuns a few seconds.)

Had to zip-tie ICM connectors together.

Post by **Larry60** » Sat Jan 18, 2020 8:34 am

Fuel pump randomly runs.
I feel relay click but no sound from pump.
Now pump rarely runs. Even then no pressure build up in lines.

Any condition that would stop pump, even with relay click? Good voltage to relay.

(I did switch relay with another of same type.)

Post by **Larry60** » Sat Jan 18, 2020 11:16 am

I should have said -
randomly does not run when it should.

Post by **itsa300zx** » Mon Jan 20, 2020 4:43 pm

I'm out of ideas other than possible power to the fuel pump or fuel pump itself. Have you checked the fuel pump relay (green, left foot panel near fuses), FPCU behind the drivers seat?

chieftolly · Post by **chieftolly** » Wed Feb 05, 2020 10:32 am

Have you tried applying 12v to fuel pump to run it manually and see if it quits? It should rule out fuel pump being bad if it stays running

Post by **Larry60** » Fri Feb 07, 2020 8:22 am

I replaced the fuel pump. But with very cheap one. Still getting 50psl while cranking. And 40+ when running on carb cleaner.

So apparently destined to replacing injectors.

Surprising, because injectors click when cam sensor is rotated.

Post by **Larry60** » Sat Apr 18, 2020 8:38 am

Finally back to working on my 300zx. Apparently all the injectors are all bad - open circuit to Ohm meter.

Pulled intake plenum and injectors. New injectors on order.

My question is about all the coolant plumbing around and under the plenum, is that necessary? or can I just bypass the plenum coolant?

Larry60

Post by **itsa300zx** » Sat Apr 18, 2020 9:30 am

The coolant line under the plenum are a common delete, I have done it and would do it again.

Post by **NolimitZ32** » Mon Apr 20, 2020 6:06 am

^ As stated, a common delete, search "300zx plenum coolant line delete" there are plenty diagrams and a few diys.

Post by **Larry60** » Mon Apr 27, 2020 8:37 pm

I'm close to putting the plenum back on. But not sure about bolt torque. Found references for 12 to 15 ft/lb

Does that sound right?

Post by **itsa300zx** » Mon Apr 27, 2020 8:46 pm

Yes, 12-15 ft.lbs

Post by **Larry60** » Mon Apr 27, 2020 9:00 pm

Post by **Larry60** » Fri May 15, 2020 10:05 am

Back together and running.
One vacuum line (not in my disassembly picture) that I don’t have location. See pictures. Where should it connect?

Suggestions? Please!!

Post by **Larry60** » Fri May 15, 2020 10:15 am

Pictures are from long view to closeup.

Right side (passenger side) branch in smaller vacuum line to crossover.

Not sure where the tube itself was connected. The before picture does not show the line and where it goes.

Post by **Larry60** » Sat May 16, 2020 10:29 am

I may have found vacuum hose. Fell way down behind engine. Runs all way across firewall to small unlabeled box. See picture.

What is it? What function does it serve?

Post by **itsa300zx** » Sat May 16, 2020 11:12 am

Boost sensor for the dash gauge.

‘91 300zx TT no start no-spark no-fuel pump

‘91 300zx TT no start no-spark no-fuel pump

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