So here we have a technical fault that was dealt with in the workshop recently, thought it may be interesting to see what you guys would make of it and see if maybe we have a budding technician or a right good guesser among the membership!! I can tell you this is a weird fault with a surprising conclusion, read it all through before making any conclusions.

 

So let start with some background first, a standard non turbo running well with no major issues that developed a small water leak, the owner with some tech help from Jamie here and some pipes removed the plenum and replaced the offending pipes, the work seem to go well but once all back together the first start up was less successful.

 

The owner went over his work and with the exception of switching the coil pack connections on number 4 and 6 cylinder could find nothing to cause the non starting.

 

However with a fresh battery charge and some long starter motor action eventually it started, this is where we gave some further advice on checking vacuum pipe connections, electrical connections etc. at this point it was realised the det sensor and near side variable valve timing solenoid connectors were the wrong way around and so with these correctly plugged in the owner happy to do a road test.

 

This is where it all went wrong! the performance was terrible with a huge performance loss, lethargic acceleration coupled with a low tickover, and a sheer reluctance to rev when stationary and in neutral.

 

 

The next stop for the owner was a very slow drive to the workshop for us to take a look.

 

So as mentioned this was very poorly running zed, as we knew the plenum had been off and the potential for air leaks after we went straight for a leak check. In all fairness there was a couple of small leaks and one major one where an air pipe had been left disconnected under the plenum on the n/side.

 

Further checks of the smaller vacuum pipes found the egr valve incorrectly connected and so this was sorted and confidently the engine was started, but argh!!! exactly the same! no improvement at all, static revving the engine just produced this weird really slow build in engine revs whether the throttle was opened slowly or wide open, a seriously muffled sound from the exhaust.

 

So to recap, the engine has serious performance issues, but will not rev, now we know there is no air leaks, no pipe work errors, no misfires on odd smelly exhaust was no surprise because clearly something's no right but either way time for the ConZult.

 

 

 

 

 

 

ConZult screen One

 

So here is the first screen shot, for the uninitiated the there is a fair bit of info on it that is important and some not to worry about but in short there is a faulty O2 sensor a good timing reading ( confirmed with a timing gun) a high iavc ( idle control ) valve reading but the temp is only 67C so again not to worry about yet, BUT take a look at the injection pulse 4.03 ms !!! this is practically double what it should be, but with a an A/F reading of 108 % it could be easy to miss it as excessive enrichment. High injection pulse can be cause by air leaks due to the readings at the air flow meter been corrupted by the leaks or and very common a failed afm can give poor or corrupted readings that are still in its total range so hence no fault code error readings.

 

ConZult screen Two

 

So trying to keep it brief the next screen shot is some time on, lots of things have been checked again and again including timing, air leaks , vacuum pipes, throttle balance tps o2 sensors disconnected and reconnected, spark plugs checked cambelt timing checked all with no improvement.

 

So this particular screen shot shows an amazingly odd set of readings if you look at the part throttle tps reading against the actual engine revs of 3,700, this again was a hard, slow and lethargic engine that was slow to pick up. The injection pulse of 12.5ms is worrying so was the awful smell coming from the exhaust serious incomplete combustion, luckily we have a very well ventilated workshop!!

 

A split second after this screen shot without any more throttle opening the engine revs to over 6k very suddenly, releasing the throttle the revs dropped to idle, each time we tried the it the same thing happened. Now this is all very odd but even more so when you consider that we had the air flow meter disconnected at this stage!!!! yes that's right an engine revving at 3,700 and upwards with the air flow meter disconnected.

AFM Disconnected

 

 

So now we have moved up a gear with an engine that does not respond to the expected fault finding procedures as with the afm disconnected the engine should not rev pass 2,500rpm, oh and no fault code appeared in the ecu memory.

 

Ok guys so what do you think? just a little bit of fun, I doubt anyone would guess the exact cause of the fault because it was a bit bizzare in a simple way but had big repercussions.

 

So to recap.

Poor engine performance

Very slow resonding revs

Odd smell to exhaust

Swapped checked

AFM

ECU

TPS

Timing checked

Cambelt checked

Leak check

Abilty to rev to 6k with out an air flow meter

 

 

 

Jeff TT

dont most engine sensors run at 0.5 to 5v?, if theres a short or open circuit within the 5v sensor circuit say maf sensor / tps it can cause problems with the other sensors on the engine

Its got to be a short somewhere, wasn't a wire trapped between the plenum and rocker cover or something similar?

was there a wire broken when the plenum took off.soo when the engines vibrating its its an intermitent circut..as to wot one i dont know

i know - it was a twin-engined Z and the problem was with the engine in the boot!

No, it was all ok before the plenum pull.

 

Jeff

 

Ah of course! Sorry only since the plenum has been off.

 

Got to be electronics/electrical though, part of the loom damaged during the removal so shorting out on the block/plenum or something?

Its got to be a short somewhere, wasn't a wire trapped between the plenum and rocker cover or something similar?

 

Mmm...there was an issue with part of the loom on the passenger side that should go under the balancer bar and was wrongly routed over the bar......( clue )

 

Jeff

o2 sensor connecter plugged into the coil pack? is that possible?!

the cover of some wiring was sawn off by the moving throttle cable until the wire made a connection with the throttle cable!?! :rofl: :rofl:

right connectors on the engine side of the balance bar are, fuel rail sensor, 6 PTU's 6Injector plugs. and when it crosses under the balance bar you have the Idle adjustment, det sensor, O2 sensor, and that other one under the idle adjustment. the Det sensor wire wasn't plugged into the O2 socket, and the O2 sensor plugged into the det sensor socket?

o2 sensor connecter plugged into the coil pack? is that possible?!

 

 

Unreal how such a simple fault was causing such problems, a real lesson in not going too technical sometimes, the loom position error was masking the issue slightly as it was short and tight over the offending coil pack, the ecu was receiving corrupted signals and been back fed on two circuits so hence the poor running and the bizzare running without an afm connected.

 

Once correctly plugged in all was in order again and running fine, a few moment readjusting a couple of settings and she as purring like a cat, the lack of detectable misfire though remains a slight mystery.

 

Anyway nice one Quavey for guessing right ( with a few hints) and well done all of the rest for making this thread interesting! want another one?

 

Jeff TT

 

Unreal how such a simple fault was causing such problems, a real lesson in not going too technical sometimes, the loom position error was masking the issue slightly as it was short and tight over the offending coil pack, the ecu was receiving corrupted signals and been back fed on two circuits so hence the poor running and the bizzare running without an afm connected.

 

Once correctly plugged in all was in order again and running fine, a few moment readjusting a couple of settings and she as purring like a cat, the lack of detectable misfire though remains a slight mystery.

 

Anyway nice one Quavey for guessing right ( with a few hints) and well done all of the rest for making this thread interesting! want another one?Jeff TT

 

 

God no lol

 

 

Only joking, go on then :clap:

yes

Yay! I never win anything lol

 

So does that stand to reason then that the o2 sensor plugs and coil pack connecter plugs are exactly the same? Any chance that the coil was trying to spark continuously rather than being timed as per the ptu hence no actual misfire. It would cause big detonation i suppose and all sorts of weird ignition which would smell bad or be a mixture of half burnt fuel etc

 

I do find these weird issues fascinating! More more more!

Well done, Start calling you Sherlock Quavey now !!

Yay! I never win anything lol

 

So does that stand to reason then that the o2 sensor plugs and coil pack connecter plugs are exactly the same? Any chance that the coil was trying to spark continuously rather than being timed as per the ptu hence no actual misfire. It would cause big detonation i suppose and all sorts of weird ignition which would smell bad or be a mixture of half burnt fuel etc

 

I do find these weird issues fascinating! More more more!

 

Lucky no damage was done with the current going to the Coil pack, after all it is a spark plug on the end of it. though i suppose the current is uprated at the coil pack.

i knew all the time . just didnt want to spoil it for the rest of you . lol

looks like jeff might have a new technician on standby

Well it'll be upped to 30,000v or something rediculas but I was wondering if the coil responded to signal from the ecu to the o2 sensor and sparked continuously.

thats just stupid :lol::lol:

 

Guessing it was cyl no 6 ??

lol glad you found this out can make sure i dont connect mine wrong when refitting my plenum