Z32 running on five(now hardly running at all) with video!

[spiffy]

Hi guys, during a longer drive yesterday i started noticing some random hesitation and stumbling during some spirited driving up the mountains. Mostly notable during full throttle pulls in 2nd. Then I learned that I could provoke it to some extent by going around 2000rpm in 3rd or 4th and then giving it around half to full throttle under load, say going up a hill or incline.
On the way home it got worse, and when I stopped for some road work it started running on 5. Then back on 6 as soon as I got up to highway speeds...
It has done this before, but only when cold. And as soon as the car was warmed up it would disappear. I swapped the plugs thinking it was a plug fouling, and it helped the first couple of drives before it started to reappear. Now it doesn't matter if it's warm or cold.
It is the nr5 cyl that stops, I have tried to swap coils with nr1 cylinder but the problem stays on the nr5.
I have previously listened to the injectors to check if one might be dead but all are ticking like they should.
My attention has turned to the PTU, but my car is a 91 TT but it has the newer style ptu so it has been swapped at some point. How prone are the newer style ptu's to failure??

[NolimitZ32]

Check to see if you have spark manually by pulling the plug , connecting it to the COP and turning the CAS by hand with the key in the on position (ENGINE NOT RUNNING). If you have spark it could be a compression loss issue if not than its most likely your PTU.

[spiffy]

forgot to check that!

Anyways I tried to troubleshoot today; started it up. Car runs fine... I notice a slightly higher idle and the fan is constantly on. Even though the car isn't warmed up yet!
So I take it for a ride to see if the stumbling issue comes back.
A couple of km's down the road it's warmed up and i can provoke a slight stumble and the hesitation gets bigger. It feels powerless, on the way back I try a full throttle pull, it's gutless and hesitates. No power at all, feels like a boost leak or maybe even like a broken maf!
So I come infront of the garage and the car just dies, I start it up again and it idles like crap, hunting, and I notice the boostmeter in the dash is a little higher than it should be when idling.
I floor it, rpms stop at 2-2500 maybe 3000 and then it dies, or if I let go of the throttle it returns to crappy idle. But I can slowly and gently raise the revs to max... sounds like a broken maf. But no fault codes, only 13 and 21; water temp circuit and ignition signal circuit.

I did these tests: http://www.300zx-twinturbo.com/cgi-bin/ ... &total=190
Except for C('cause I don't have a logic probe), but I tried to connect a test light and it lit up and blinked sort of, so I guess signal is good :/
I also tried the ptu check, page 179 in the EF&EC section, http://www.300zx-twinturbo.com/cgi-bin/ ... &total=190 there wasn't any continuity anywhere there should....

[spiffy]

does anyone know how to test the newer style ptu? since the servicemanual I linked to uses the old one.... I figure I need the fsm for a 94 model Z.

I also forgot to mention after I drove the car in to the garage the smell of unburnt fuel was pretty strong. How much can a broken water temp sensor f**** things up?? Could it be its drowning ? is that the reason(or one of it) it dies on accelerating?

[NolimitZ32]

Sounds like you're in limp mode, check all your hoses for vac leaks, also check inputs and outputs on the maf and TPS

[spiffy]

I'll do that, but I found a service manual covering the testing of the newer ptu. I just tested it and it failed all tests... No continuity at all...

[spiffy]

Today I tested the water temp circuit, without a fault. Voltage was around 4.6 at cold and dropping as the engine warmed up. But idling got worse as the engine warmed up... I also had problems checking the resistance of the sending unit, I tried testing another one I found in the garage(from a datsun) and had no problems getting a good reading from that as opposed to the one in the Z. I'll unscrew the Z one and test it in a controlled enviroment...

I also checked the cas, wich is good, I sprayed startergas around all the air hoses I could find and on/around the intercoolers but couldn't notice any difference, I also tested the MAF, wich where within the specified 0.8-1.5V range with 1.45 at idle(engine warm)
It was however out of range with engine off, ignition "ON", it showed around 0.48 while the servicemanual says it should be 0.8V, I'm not sure if it has anything to say at all....

Also, the ignition fault code is gone now.... Don't ask me how or why, I have not done anything except taking the ptu out of the car for testing(wich it failed) and then reinstalling it...

I'm probably gonna replace the water temp sending unit on monday and see if it makes a difference.

[spiffy]

Got a new temp sensor for the car today, swapped it. No difference except the fault code is gone.
The car itself still runs like crap. But no fault code, only "55".
The needle in the vacuum gauge is one bar higher than it should be at idle, anyone know how or why this might be?
I'm gonna remove the front fascia tomorrow and check IC's and spray around with start gas to see if I can find any leaks but if not them I just don't know what else to do....??

[GerryO]

does anyone know how to test the newer style ptu? since the servicemanual I linked to uses the old one.... I figure I need the fsm for a 94 model Z.

I also forgot to mention after I drove the car in to the garage the smell of unburnt fuel was pretty strong. How much can a broken water temp sensor f**** things up?? Could it be its drowning ? is that the reason(or one of it) it dies on accelerating?

The best way to check injectors is with a multi-meter and they should read about 11.5 ohms. How many miles on the car/engine? ECM trouble codes will only indicate things that are in some way electrically wrong; a wiring, resistance value/sensor issue, or a vacuum/temperature control solenoid that isn't opening or closing when it should.

Could be an injector that is leaking, a faulty fuel pressure regulator, a leaky injector o-ring or spark plug that's now fouled.

Pulling the plenum is a very good thing to do on an engine this age, as so many hoses and o-rings have gotten brittle and just as many things need a thorough physical and solvent cleaning. Running so rich could also do in your catalytic converter and it's probably time to replace O2 sensors too.

[spiffy]

I have pulled the front fascia off. Sprayed around and checked the hoses to the IC's, didn't find anything unusual.
Still no fault codes, I did the exhaust sensor monitor test and both sensor are indicating lean(engine light on=lean, engine light off=rich). It should alternate at least 5 times in 10 seconds but mine does not. So either BOTH sensors have gone at the same time, or there is something wrong with fueling.
What a friggin nightmare!

[spiffy]

VIDEO: http://s2.photobucket.com/albums/y41/ne ... EO0020.mp4

any input?

[spiffy]

This is my fuel pressure, at idle.... Should be 2.5 bar, 2.9 when disconnecting fuel pressure regulator vacuum hose. Nothing happens when disconnecting it.
I hear my fuel pump going, and squeezing the fuel hose makes the pressure rise, so the pump is doing it's job.
I'm gonna order a new FPR and hope everything turns out OK.

[kelseh]

I had no power, stumbling at idle, running like crap. It was two things. One was that the connector to the ptu on the side that runs to the ecu, not the coil packs, was loose. It was missing on cylinder #6. Check that the metal retainer is on properly. That fixed cylinder 6 not firing. Also the new o2 sensors fixed the rest. It runs like new again after she warms up. They were stock on lean and you could smell unburnt fuel.

[spiffy]

Yeah I noticed one connector on the ptu was loose as I was removing it. Probably the cause for the fault code and missing cylinder.
The problem now is I have no fuel pressure, so the car is barely managing to stay alive on idle...
I have ordered a new regulator but those things aren't in stock here in Norway so they have to be ordered from nissan in the Netherlands. It's gonna take about a week for me to get it.
I'm praying it'll all be good then as I have a show to attend in the beginning of june