After some advice please,

Ive owned this car for about a year now (jap tt) and during the time ive owned it, its been reasonably reliable, except for an unresolved boost issue and it now needs its 4th injector. Please ignore the boost problem as I dont think its relevant to this issue. When I bought the car it had a few dodgy "fixes",I think ive sorted all of them and interestingly it was sold with a bag of 6 standard injectors as it had upgraded ones fitted (it didnt).Every now again it runs on 5 and by swapping the injector with one from the bag it runs on all 6 again. The dropped cylinder is moving, so in my opinion would rule out a wiring fault. The plenum has been dremelled so swapping hasnt been to much of a problem until now. The dead injector is the back left cylinder as you look from the front of the car. ( not sure of numerical layout). So im gonna remove the plenum to do this one and do the deletes at the same time. The advice id like is, how likely to lose 4 injectors in a year? Could this be something other than injectors? I jave a third working set of injectors in another engine I could use, would it be worth getting these ultrasonic cleaned? Or do I just put a new set in? Any help would be appreciated as always, thanks.

Have all your failures been the original ones? I.e. None of your replacement ones have failed? Also these replacement ones, are they new or second hand.

What year is your Z? Are these phase one (square top injectors)? What fuel are you using?

Have you checked your PTU connections for damage/corrosion? Same for injector connectors.

 

Are you running an early style PTU which can fail giving similar conditions to the one you describe?

Edited January 15, 20178 yr by AndrewG

Have you checked your PTU connections for damage/corrosion? Same for injector connectors.

 

Are you running an early style PTU which can fail giving similar conditions to the one you describe?

 

These are good points, although I'd taken from his comments than the fail was not intermittent. So therefore if it was the PTU changing the injector would still render that cylinder down do to loss of spark. I'd be interested in what method was employed to diagnose the injector itself at fault.

Depends on how you frame "intermittent" - the OP does state that "Every now again it runs on 5" and "The dropped cylinder is moving".

 

Not discounting your suggestions, rather giving other things to check and eliminate as causing the problem.

Edited January 15, 20178 yr by AndrewG

Depends on how you frame "intermittent" - the OP does state that "Every now again it runs on 5" and "The dropped cylinder is moving".

 

Not discounting your suggestions, rather giving other things to check and eliminate as causing the problem.

 

My apologies for not explaining clearly. When it runs on 5, the 6th cylinder does not "come back" until I swap the injector. It is not an intermittent problem. When I said the dropped cylinder is moving, I meant that the failing injector has not been on the same cylinder. By diagnosing the injector, first I swap coils, then plugs, then screwdriver test and then swap injectors. I would/should ohm test, but my multimeter is dead. Been meaning to get a new one for ages.

I think the problem is almost definitely just the injectors, having eliminated most other options. It just seems unlikely to me that I would lose so many in a relatively short space of time. I am on a budget, so I dont want to waste money making the wrong decision.

Sorry did answer all posts in that last post, but seem to have lost some of my reply.

Ptu and injector connections have been checked and cleaned, ptu was swapped 6 moths ago with a spare. None of the replacement injectors have failed as far as I recall, car is 1991, so phase 1 injectors. The injectors are not new. Always run on tesco premium unleaded.

Depends on how you frame "intermittent" - the OP does state that "Every now again it runs on 5" and "The dropped cylinder is moving".

 

Not discounting your suggestions, rather giving other things to check and eliminate as causing the problem.

 

Didn't think you were bud ;) just expanding the discussion.

Any ideas anyone?

The phase 1 (square cap) injectors are less reliable than the later more modern oval ones. They are prone to damage from high ethanol content fuels. As well as a quirk of the loom that they are permanently live, even with the ignition off. This was revised in later models. Now obviously you can't know the history of the car fuel wise etc, coupled with these being 23+ year old electrical components failures aren't to be unexpected. It's also not unreasonable for them to fail at a similar time due to that.

What you should do is ohm test them and keep a track on which ones have stopped working. Repeat failures would cause a warning flag to me. The best option would be to replace them with the later ones. I realise that may not be an option. Second best option is to have a set cleaned and flow tested. Then fit all 6.

Sadly without even ohm testing them how can you be sure it's even the injector at fault. I know you did the screw driver test but that only tells you the circuit is there or not as the case may be. All your proving with that test is that the injector isn't firing.

Time to go buy a multimeter.

Already on the multimeter, should have a new one tomorrow. With regards to the injectors, if I were to change to the later style, I would need injectors, rail and connections. Anything else?

Not that I'm aware, as long as you swapped for the same size. You can use adapters rather than replace the rail. There's some seals as well, may be part of that kit.

Anyone want to chip in and clarify?

In my experience the earlier injector failures are caused by the poor connection, any electrical circuit that has poor connection draws more current and in turn the circuit warms up, this is what cause the small injector coil insulation to fail, during this time any Ohms resistance testing will indicate how the insulation and coil integrity is holding up.

 

The internal coil winding legs also can corrode and snap, this is when you get an open circuit and total failure and by far the most common fault, the later injectors had more robust connectors that all most certainly eliminated the connection and high current load issue, along with the earlier circuit wiring that continues to stay live even when the engine is switched off. Any green gung in the connector along with any moisture present will react with the voltage present when the engine is switched off and cause more problems.

 

The high ethanol content issue was a US problem not in the UK as their allowance is three times what is or has been allowed in UK fuel, in every single injector failure I have seen / worked on it is either a very high resistance coil or an open circuit one not pintle damage.

 

In fact provided the original ones are kept clean they will give long, long service, many zeds were are talking about now are still running on original units 28 years on, cannot really call them weak.

 

Jeff

That's a very informative post Jeff, thanks.

Thanks stephen and jeff, very helpful. Jeff in your opinion, is it worth changing to the later spec injectors?

Thanks stephen and jeff, very helpful. Jeff in your opinion, is it worth changing to the later spec injectors?

 

If you're planning on going for more power anytime in the next few years, I'd say yes, get all the bits you need to change for a laters injector. However, as there are now a fair few options available, I would go for a top feed rail setup over a side feed setup. The new generation top feeds are a very stable injector platform and if offers you more injector choice.

 

If you have no plans to go above a slight boost increase or don't plan on keeping the car in the long term, stick with old style side feeds. It's not worth the expense to upgrade.