Motor won't crank...spark output appears 'flaccid'

[swvasasquatch]

A few months back, my son bought a 90 ZX non-turbo, approx. 150k miles. It had an obvious oil leak which he was determined to remedy. What he thought would be a two day valve cover gasket job turned into a 6 week ordeal during which motor and transmission were pulled and a plethora of parts were replaced until funds and patience (guess who got sucked into helping him) were exhausted. Due to loss of aforementioned patience, some haste and ill-advised creativity may have been applied during re-assembly.

We had some trouble with a couple of cylinders during initial start-up. Spark was strong, fuel was pressurized, so apparently the problem was finicky electrical connectors to injectors on 1 and 6. Lo and behold, once all six injectors were firing the damn thing ran like a scalded dawg. Then things started to go down the ****ter.

EGR was 'abandoned' during re-assembly. Cheesy rubber plugs that were hastily utilized to cover holes where tubes entered intake manifold were soon sucked into said manifold.

My son had found a couple of three-wire O2 sensors on a zx website. OEM connectors got 5 wires though. Utilizing genetics gifted to him from my X, he frankensteined the sensors/connectors by doubling up wires of 'same color' so that 3 wires went in a mass of elec. tape, and five came out.

Weird electrical things then started to happen...capped off by sensor wires on passenger side erupting in flames. Refusing to admit wrongdoing (this is where my genetics kick in) he unplugged the sensors, stuck corks in the EGR holes, and promptly embarked on a 200 mile trip to a w/e 'music festival'.

By his account, car ran fine for the first 100 or so miles. He punched it to pass a car and then things started to go down the crapper. Motor started dropping cylinders, but he persevered and made it. When his 'three days of fun and music' were over, he couldn't get it started in order to get his *** back home.

Guess who had to go get car and haul it back home. My son is off to college now and I have said car clogging up my driveway. Which brings me to my topic, finally.

I just started trouble shooting. I replaced the O2 sensors with the proper ones. EGR holes are plugged. When I crank the motor, it wreaks of fuel. I pulled plugs 1 and 2 around dusk and checked for spark. Both plugs displayed an erratic, pathetic attempt of a spark. Certainly not the white hot potent spark I observed during Troubleshooting session #1 a couple of month back. What should be my next move? I apologize for going all the way around my *** just to find my elbow, but I'm speculating that rushed non-expert reassembly and said events leading up to this will resonate with someone who is now an expert at trouble shooting these cars.

[Zwicked]

Either a close to dead PTU or the CAS plug is not making good contact are the first 2 things I would look at as they both relate to firing the coils and injectors.On this really quite fantastic car, there are 2 failings as a result in my mind where the Nissan engineers obviously partook in a day time office party which included a lot of Sake intake. The connectors with the spring clip and the gen 1 injectors on this car are it's nemesis which most people must revisit many times through owning it.

PS - entertaining story by the way.

[swvasasquatch]

Thanks for the input...however please excuse my ignorance. I need to be schooled on what 'ptu' and 'cas' stand for, and where their location on vehicle might be. Both sound expensive and extremely electronic in nature.

[Zwicked]

They are both expensive. The CAS rarely goes bad and the newer PTU's are also pretty solid.

The PTU (Power Transistor Unit) is on the front of the timing belt cover on the passenger side. The early prone to failure type is silver in color. The updated one (92 and newer) is black and requires a short sub-harness for it to fit on the 90-91 cars.http://www.z32photoguide.com/ptu.html

It can be tested with a multimeterEngine Fuel and Emissions Control section, page 179

http://www.300zx-twinturbo.com/cgi-bin/manual.cgi

The CAS (Crank Angle Sensor) is on the driver side front of the engine and is used to set the base timing and carries the signal. The plug is a bit of a pain to get off, but it's very common for it (and all) to become corroded and not make good contact.To test injector and coil pack firing, it can be removed, harness left on. Turn ignition on and turn the CAS shaft slowly be hand. You should hear each injector click. You can also test the coil packs in the same way if you insert a spark plug and ground it to the engine to watch the spark on each as you turn it.

Bottom photo

http://www.z32photoguide.com/sensors.html

Don't hesitate to email me if you have questions

[skinZ32]

thanx zwicked for the z32photo website. been looking for something like that for a while

[swvasasquatch]

I've been troubleshooting my PTU and have noticed a weak spark coming from each coil pack. I wondering where the common ground is for each of these. Where does the common ground from the coil packs go?

If this ground is bad would that cause PTU failure?

[300freekzx]

You can get the PTU for cheap at a Junkyard off of a J30