Hello Everyone, I just bout a 300zx TT from a friend which got demolished by pack rats. I'm excited to get the car running, but am a little stumped at the moment.
The car turns on no problem but runs on five cylinders and I have come to the conclusion that its because I get no spark. Now it appears that the pack rats did some work on the wires to the coil pack, but I reconnected them and still no spark. After a little more testing I found out that the middle wire is the wire that carries power, I believe it was the left one that grounded it(which both are doing exactly what they should), but the third one I have no idea and im assuming is the problem to my issue. After a little bit of research I believe that this wire connects to the power transistor unit(PTU), and looks like this fails quite often from all the other posts that i've seen.
Now my question is pretty simple, Would or could the PTU cause only once cylinder to not fire? Or should I simply be looking for a chewed through wire?
Some more information that may be helpful. I changed the spark plug with a different cylinders and the spark plug was NOT the problem. I changed the coil pack with a different cylinders and it was malfunctioning BUT the original cylinder still misfired.
Thanks for any and all help.

 

If the PTU is the newer style, it is not likely to be the problem.

How have you determined that the problem is spark? Fuel injectors are very problematic on pre-94 TTs.

 

I decided it was because of the spark because of a few reasons. First one being that when I pulled the spark plug it had fuel on it, and secondly because I did the whole screwdriver test and it was clicking as normal.

 

That's not a valid injector test... all it tells you is that it's firing. It could be firing too much, causing your plug to be covered in fuel and not igniting because it's too rich. Test the resistance across the injector leads, it should be 10-14 ohms.

 

Ill have to get a multimeter tomorrow to test it and ill post the results. Thanks for the guidance.

 

before you do that, you could check for spark. requires no special tools and may show you your problem.

 

How would you test for a spark? I have been told to pull the spark plug and connect everything together and ground the spark plug and try to start the car to test it, but wouldn't that cause fuel to spew everywhere which wouldn't be a good idea with a spark plug that might ignite it? Should I just remove the fuel pump relay?

 

no, fuel wouldn't spray everywhere. the injectors aren't spraying that much.

and you don't necessarily "ground" the plug. you hold it close to a ground, so as to view the arc.

you've got the idea though.

 

It appears to me that you don't have a good grasp of the fact that the injectors spray toward the back of the valves and what enters the cylinder is just a light mist of fuel.

KasbeKZ, what do you mean you don't ground the plug? Yes you do. The arc that you're observing should be from the electrode of the spark plug, and the plug will not fire if the threads are not grounded (they are usually grounded to the cylinder head into which they are inserted).

 

you put me in a tough position here. i must do it...

i, kasbekz, submit, that zlover4life, is wrong. hold the plug away from the plenum and turn the engine over, and the spark will arc to the plenum. this is how i always do it. it's just how i was taught to do it. i've done it with several types of cars/plugs/coil configurations.

but, thanks for pointing out the technique of actually grounding it. that would be easier if only to hold the plug still.

what you're thinking is that if it's not grounded, it has no where to go, and yes, but, if it's close to the ground, it just jumps.

 

Your right, I didn't have a grasp on that thought. But then again that's what forums are here for, and now I can run that test with a little piece of mind.

 

I am not wrong. If the plug is not grounded, it cannot spark. You're holding it close enough for it to ground, but that doesn't mean it's the correct way of doing it. When the spark plug is in the cylinder, it is grounded and the arc is from the electrode (you know that). When you want to check it, you simulate the conditions in the cylinder (i.e. the coil connected, with the spark plug at the end, and the plug grounded to something), in a situation that allows you to observe the spark (from the electrode, because that's what's supposed to fire).

You were taught wrong. In fact, I wouldn't be surprised if your method could give a false result... if there is a problem with the electrode, your method won't show it. Your way is basically only good for testing wiring and the coil itself. (But since spark plugs themselves rarely are the cause of misfiring, that's usually what's more important to check anyway.)

 

that may be so (that my method may give a false result). but if the spark plug is not touching anything, can we say that it is grounded? it is certainly arcing.

 

Electricity can flow through many mediums... including air. Is it securely grounded? Nope... but the proximity allows the circuit to be completed.

Think about it this way... the way a spark plug works is by charging the plug so much that it jumps the gap from the center electrode (which is protruding from the center of the plug) to the ground electrode (which connects to the threads, which are grounded). If there is a short inside the spark plug, your method would still arc... but the spark plug would not fire, because the electricity would never jump the gap inside the cylinder (essentially, it'd just flow through the walls of the spark plug). What you want to verify by testing a spark plug is that there is spark at the gap of the plug, because that's where it needs to be to ignite the air/fuel mixture.

My stance is still that the injector needs to be tested first. Then we'll move on to whether or not the plug is actually firing. I'll bet that it is, and if it wasn't, it was because the injector was fouling it.

 

reading back over your posts, i guess i don't have anything to actually say "you're wrong" to, though they do all have edits! i was under the impression that you thought that if the threads weren't touching anything, then no spark would occur. but, you never said that. i retract.

 

Third philosophical imperative is to question one's own statements - so I re-read everything I say multiple times and edit to eliminate any obscurity/ambiguity that could result from my word choice.

But I certainly never said that a spark couldn't occur... I simply said that such a spark wouldn't tell you what you want to know.

Be careful with when you call someone wrong.

 

I did the continuity test and it was just at 12 to 12.1 ohms. I also did it to another injector just to see what it would read and it was a little over 14 ohms.
Ill do the spark test soon, I just need to refuel after that treturous day at work.

 

well, before the edit we had a different debate!

 

I never said that your way wouldn't spark... just that it wouldn't be the proper type of spark. As I understand, you misunderstood me (and acknowledged that).

 

Well I had no luck with the spark test on account of my battery being dead. I tried jumping the car and the coilpack started to smoke and the plastic started to bubble up. I believe this is what caused the coilpack to go out in the first place. Any ideas what would cause this? short in the wire? to much voltage? Does anyone know how many volts should be running through each wire to the coilpack?

 

It's definitely symptomatic of a short... where was the coilpack when it started doing this? I'm not sure of the voltage at the coilpack wires... never had a problem with mine. Search twinturbo.net - I've seen it discussed on there.

 

yes i understand that i misunderstood you. i was just trying to make you say what you edited out! it's no big deal. just bored. exams week, and all mine are actually easy.

 

The 12:27am post, I consolidated two paragraphs into the third paragraph, since they were related and I had a redundant statement.

In the 12:41am post, I added the entire second paragraph.

I don't delete main points... if a main point I'm considering to post is wrong, I generally catch it before submitting it (I proofread about twice before even posting).

 

man i was just ribbin'! giving you a hard time. i know you wouldn't change it to make yourself right and not point it out.