Advice needed on some interesting engine troubles..

[NemesizX]

I've recently had an issue arise with my twin turbo.

I've noticed she runs a little lumpy on idle with the occasional mild misfire. I decided to get myself a free version of consult and plugged it in.

The readings I got back that I've been advised are out of place are the aac/i-acv readings are at 44% and the idle speed is dancing around the 900 rpm area. At points the engine does run lower but it seems to wander around a little when the mood takes it.

The error code on the diagnostic is also showing code 34 knock sensor. This is obviously going to play around with something if the knock sensor is dead.

I am going to cancel the knock sensor error by inserting a resistor in to the circuit and removing the knock sensor as advised by Mark, but whilst thinking about things this morning, I'm wondering if the knock sensor is OK, but it's showing the code because it's picking up the misfires? Is this a possibility?

I'm.still running a series 1 ptu and I'm fairly sure I have a dicky coil pack somewhere thats causing the misfire. Not sure when the plugs last got changed either. So do you think I should change the ptu, plugs and coil packs before I remove the knock sensor from the circuit?

Or would the code be nothing to do with misfire?

 

Any thoughts out there?

[NemesizX]

 

Here's the read out.. Ignore the temperature reading as it remained the same once it was up to running temperature.

[groover]

The knock sensor is a known common fault on these cars and like a fair few including mine, the signal from the sensor to the ecu can be triggered by a knackered sensor or broken wire, the easiest solution has always been to do the resistor mod, therefore fooling the ecu into thinking all is well. This is by no means the best solution on a high powered zed, being constantly pushed to its limits, however for a daily or weekend runner perfectly acceptable until the chance arises to change the sensor.

 

Highly unlikely a dodgy coil pack is to blame, a new set of correct heat plugs wouldnt go amiss, but i doubt the code will be rectified until the sensor is either replaced or bypassed with the resistor.

 

If your car is up to temp, then look at the temp sensor, the ecu is obviously reading the incorrect figure and therefore compensating, which is why your your idle is too high, also IACV as you are aware should be around 14% at idle, so before adjusting anything yet, i would check your injectors and plugs, coil pack and temp sensor plugs for corrosion, otherwise you are going to struggle to maintain a good idle if you have some missing.

 

The temp sensor and resistor mod will likely sort you idle :thumbup1:

[JeffTT]

Ok NemisizX, you have done what many zed owners do and understandably given some of the innovations the z32 had on board in 1990 and that is when faced with a running problem is to go technical too quickly.

 

The advise so far elsewhere and above of which some is not too accurate are starter points but you have some basic engine work to do to resolve this very simple issue, the diagnostic software is great and without it it can be near impossible to find some faults easily. But the results can often be misleading to the untrained eye and even some who propose to be "in the know" knowing what it is NOT telling you is often more important than what it is, along with various readings been effected by anyone of the other "bad" readings and can lead to confusion, experience with the ConZult or similar systems takes a lot to fully understand and how to act on what you see so don`t feel bad your not really understanding it yet, takes about 10 years or so so stick with it (lol)

 

So first off before any other work or diagnostic is done you need to check why the temperature is so low, first check the temp sensor connection and if no problem then you will need to change the thermostat! the temperature reading is shouting at you LOOK AT ME!! at 64 deg your still in the cool engine cycle, the ecu is running the engine according to the water temp along with other values. No point doing anything more until the temp sensor / thermostat has been changed, with such low temperature registered in the ecu even if you had a working det sensor the engine would stay in safety boost.

 

Once the temp issue has been resolved and you have a tick over temp of around 80 deg only then can you check the running of the engine on the ConZult, things such as the tps look to be set ok, just check the closed throttle position and do an ignition timing check using a strobe light, this is the ONLY way to check the timing correctly as the CoNzult does NOT report actual engine set timing just whet the timing should be based on other parameters.

 

Spark plugs can make a world of difference to the running on this engine and for the small cost would suggest you change them also along with air and oil filters if due a change, oh and do not write off the series 1 ptu just yet, although these have a history of failing the issue is caused by internal heat generated by bad connection and excessive current draw melting soldering connections, no maintenance cleaning of the connections is what the real problem is, the series 2 ptu`s however fail ( and yes they do ) from actual component failure inside.

 

Aside from the running issue above the det sensor fault code suggests the det circuit is at fault and this could be the det sensor, short loom cable or the cable back to the ecu. You can if you wish disconnect it and use a meter to check the cable back to the ecu but most times its the sensor and usually melted at that, nothing wrong with a well serviced and well set up engine having a by pass fitted, tried and tested and would suggest there are not that many still with the original sensor fitted and working anyhow, more I image driving around in safety boost with unsuspecting owners, so rest assured the det sensor does not cause misfire or running issues and will not be picking anything up at tickover.

 

Link below is one of my tech thread about the thermostat and the issue with cold running, worth a read.

 

 

Jeff

 

http://www.300zx.co.uk/forums/showthread.php?126426-Thermostat-tech-tip&highlight=thermostat

[Gaz 300]

Isn't it great having Z experts on the forum willing to help members :bow:

[NemesizX]

It's magic Gaz! I'd be lost without them.

Thanks for your advice Jeff.

The only thing I will say though is that the temperature at the time of the screenshot was low but when the engine was up to its usual temp on the the gauge, the consult was reading 78 degrees and the other readings remained exactly the same.

I shall run through the things you've advised and see what I can find. I know the knock sensor is definitely dead as I've tested it and it's reading open circuit.

Resistor on the way as we speak! Lol..

Without the car being driven, is 78 a reasonable temp considering outside weather is 3-4 degrees?

I've not long cleaned and re oiled the k&n filter and it did improve running and also changed the oil and put a k&n oil filter on too.

Plugs, I'm not sure what's in it or when they were last changed so that's a must and was going to do that shortly. What plugs would you recommend? I was looking at the iridium plugs but also seen the hks heat grade 7 plugs online so confusion of choice sets in yet again.. I'd be happy to take the experienced advice here!

Need to check the water temp plug but never had any temp problems, always remained perfectly placed in the centre of the dial, although I understand about thermostats sticking open a little or a lot! I'm fairly sure there's one in there but I wouldn't be shocked if there wasn't!

I'm suprised at what you say about the ptu though, I was told the series 2 is a more reliable unit and improves running?

 

I guess it comes down to the difference between opinion and experience again! I know which one counts Jeff!

 

I'd love an experienced person to come give me a hand one weekend, but with no garage it's a big ask for someone to help and expect them to freeze their bearings off too.. God knows I've lost mine out there on occasion! Starting to build up a whole heap of jobs, so think my first buy will be a waterproof jacket and a pair of thermal pants...

[JeffTT]

the temperature at the time of the screenshot was low but when the engine was up to its usual temp on the the gauge, the consult was reading 78 degrees and the other readings remained exactly the same.

"Here's the read out.. Ignore the temperature reading as it remained the same once it was up to running temperature."

 

Ok your text under the screen shot was a little ambiguous sort of sounded like the temp stayed the same not the problem but can see what you meant now, try running the engine with the AFM disconnected see if the running issue changes, also check the egr is not sticking and hot wire afm`s generally do not get on well with oiled filters as it can propagate through the system and contaminate the wire.

 

Jeff

Edited January 13, 2016 by JeffTT