Misfire woes

[DatsunMan]

Engine fault - HELP please!

1982 280ZX electronic ignition & fuel injection
Starts fine, runs on all 6 initially
After a short while will start to run lumpy
Removing a plug lead, either 1, 2, or 3, makes no difference...
Removing either 4, 5, or 6, the engine will stop
So, I appear to be running on half an engine!
Then it will cut back in & run on all 6 again, then drop out again to effectively just 3 again
This is the same when under power

Any ideas please?
What links 1 to 3 differently to 4 - 6 ????????

Thanks!
Regards, Geoff
07980 936438 anytime

 

[candy red]

Have you checked you have a spark at the offending cylinders pull the plug see what condition there in

Check fuel pressure with inline gauge,
Check fuel filter.
Check all electrical connections to fuel injection system faulty or dirty connections can make a big difference to how it runs .
good luck

Derrick

 

[Ped]

I had a mystery misfire for a while and couldn't work it out. I had it in at a fuel injection specialist who did fix a faulty connector which helped a bit, but the test continued to show an intermittent fault. They couldn't pin it down so suggested swapping out the usual suspects ie: dizzy cap, rotor arm, plugs and leads. All these items looked to be in good condition, but I swapped out the dizzy cap, rotor arm and plugs and it fixed it.

If I were you I would start with these items. If this does not fix it you can just put them back in the box for future use.

 

[DatsunMan]

Candy Red & Ped,
Thanks for the replies & suggestions.
I forgot to say that I have changed all the plugs, & the gaps are correct!
If the fuel pressure was incorrect, why would it only affect 1 2 & 3 cylinders?
Likewise the fuel filter?
Equally, if electrical connections are faulty/dirty, how do they work ok some of the time?
There is a good spark at all 1 2 & 3 cylinders when I remove the leads, but the engine keeps running...
But when 4 5 or 6 is removed, the engine stops
So, I do suspect a fuel issue, but why would that only affect half the engine?
It's a mystery all right!
I was rather hoping someone knew something that was different to 1 2 & 3 as opposed to 4 5 & 6 ?
Or maybe there isn't anything?
I have put £50 of super unleaded in it, just in-case it was the quarter of a tank of older fuel? No change!
Any more suggestions very welcome of course...
Thanks again.
Regards Geoff.
p.s. Only just bought the ZX, so I havn't even driven it without fault yet...very frustrating...

 

[DatsunMan]

I forgot to say that I have changed all the plugs, & the gaps are correct!
If the fuel pressure was incorrect, why would it only affect 1 2 & 3 cylinders?
Likewise the fuel filter?
Equally, if electrical connections are faulty/dirty, how do they work ok some of the time?
There is a good spark at all 1 2 & 3 cylinders when I remove the leads, but the engine keeps running...
But when 4 5 or 6 is removed, the engine stops
So, I do suspect a fuel issue, but why would that only affect half the engine?
It's a mystery all right!
I was rather hoping someone knew something that was different to 1 2 & 3 as opposed to 4 5 & 6 ?
Or maybe there isn't anything?
I have put £50 of super unleaded in it, just in-case it was the quarter of a tank of older fuel? No change!
Any suggestions very welcome of course...
Thanks again.
Regards Geoff.
p.s. Only just bought the ZX, so I havn't even driven it without fault yet...very frustrating...

 

[candy red]

Are the plugs wet with fuel when there not firing i.e. 1,2,3

how long does it run on all cylinders

 

[Huw]

Hi Geoff

Its a bit difficult to give you a straight answer to you conundrum as would really do with a bit more info. You say its missing, is it all the time, what happened under load or when you rev it, is it missing from cold or when up to temperature etc.

Rather than making stab in the dark suggestions I would recommend you down load the EFI service manual at the link below and follow the check lists within it. The site also has comprehensive service manuals too.

http://xenonzcar.com/s130/othermanuals/1980efimanual.php

However, quick stab in the dark checks would be:

Check vacuum lines, check for leaks and splits in the pipes
Distributor cap condition, cracks or corrosion on the contacts
HT Leads - check the spark for each plug at each HT lead as you crank it over. doesn't matter if the engine wont run just crank it and look for a spark.
Leads to the Ignition module on the distributor, check for damage or loose cables - maybe the module itself (black box on the side of the dizzy) they do fail.
Check the condition of the coil and the leads and connectors for the low tension. The coil could be weak and starting to break down as it get hot.
Check the cables to the temperature sensors at the front of the block (yes i did say that) for corrosion as you say it gets worse once warm.
Check the plugs to each injector are making good connections
Fuel filter, replaced anyway as you don't know the history of the car.

If none of those, get a multi-meter and start the checks in the EFI service manual as above.

Its a case of running through systematically until you find the fault if you can't see anything obvious.

Let us know how you get on.

Huw

 

[DatsunMan]

Candy Red, thanks again, & in answer to your questions:-
Haven't checked if plugs wet when not firing on 1 2 or 3 yet, but it does fire again quite soon still...
Runs on all 6 at least 50% of the time, then drops to 3 the other 50%!
It's so 50/50 that's it's hard to track it down, as it starts to run ok again as soon as you start to investigate...
Huw, Thanks for your advice, & yes, I think that's all I can do, systematically remove, clean, & replace everyting fuel-wise & ignition-wise...
Watch this space!!
Cheers

 

[racer]

If I remember rightly the early drop in resistor was split in half with 2 separate plugs. Poss each half covering 3 cylinders? It's been a long time since I've had a 280 to be honest.

Either that or maybe a intermittent dizzy fault?

 

[Ped]

Hi DatsunMan, even if the dizzy cap and rotor arm look OK (as mine did), there was a fault with mine, so as these are cheap and easy to swap, I would try that first. It is a process of elimination.

 

[monza]

The ecu fires in banks of 3 ( ie 1+2+3 and then 4+5+6 ). One single 12v feed supplies the injectors via the series resistors. I think the series resistors control 4+2 not 3+3.

I would check all efi connections and earths - wont take long, and definitely remove the main ecu connector to check for poor connection / damp / corrosion. You may have to open the ecu to look for tide marks or corrosion - but perhaps not as a first step....

You need to confirm spark when its drops to half the cylinders - get those cheap plastic caps with lights in that plug into the plug lead and work with the engine running - you may even be able to drive around with them fitted, so you can leave them while you wait for the problem to occur.
The injectors are noisy and you can hear them fire easily - so use the screwdriver to ear trick on each one to confirm that they are firing when the problem occurs.

If you see this post or similar twice then its because my pc 'wobbled' when posting !!.....

Cheers

 

[DatsunMan]

Hi, Racer, Ped, & Monza,
Thanks for all your help with this.
I think Monza might just be on to something, with the ecu firing in banks of 3 (1-3 & 4-6)
That's exactly how the engine misfire seems to present itself, with half the engine having no effect at times...
Also, the noisy injectors do all seem to be clicking, although to be fair, even tho removing the leads from 1, 2, or 3, has little or no effect on the engine running (when lumpy) there does appear to be a spark there still (as I do get a kick from it, & here the spark jumping the gap etc.)!
One final clue - the car has done less than 1000 miles in the past 4 years, so not really been used...
In fact, it's only got approaching 38,000 on it now, & that is genuine!
Compression test produces circa 190 on every pot.
Just wish it would stay running smooth tho, it's sounds & looks fantastic when it does!
I keep you all posted! Of developments!!

Meanwhile, it need new disc pads, front & back, a new exhaust system, & new wheels & tyres...
Yes, they're the metric wheels with Dunlop Dunovo run-flat tyres on still...20 years old?!

 

[candy red]

Would be good to see some pics of your car

 

[DatsunMan]

Happy to oblige with some photos...but how do you attach/upload photos here please? Thanks!

 

[Rob Gaskin]

Happy to oblige with some photos...but how do you attach/upload photos here please? Thanks!

Did you see the PM I sent you?

Photos.

People do it in different ways - I use the following method for attaching to posts:

Write a post and the click on the 'paperclip' icon. click of your picture/s only about 3 per post is best, upload, close window and click reply. They should appear but will be small - Steve Burns will resize ASAP for you.

 

[DatsunMan]

Can't see a paperclip icon, unless it's the one that says 'insert link' ?
which then says 'please enter the URL for your link' ?
If this is the one, I still don't understand it!

 

[DatsunMan]

No, no PM for me!

And I just posted a quick reply, which doesn't seem to have loaded eithet!

 

[DatsunMan]

Ahh, post now loaded!!

 

[jonbills]

Click 'go advanced' then you'll be able to add an attachment with the paperclip icon.

 

[Rob Gaskin]

Can't see a paperclip icon, unless it's the one that says 'insert link' ?
which then says 'please enter the URL for your link' ?
If this is the one, I still don't understand it!

If I click 'reply' I see this. Is it just me guys?