OK, so been looking at Det again toady. Bear in mind, Thor O2 sensor clearly showed that this was leaning out not timing. This was on both my car and Leigh (Friday's) mine with various maps.

 

So today, replaced FPR with new one (thanks Leigh) and connected up fuel pressure gauge. Result: 3bar with atmospheric on vac line, constant 3bar + boost under load, similar story on Leigh's car. So no pressure problem, but STILL DETTING!

 

Other stuff done - EGR system disabled by removing sol valve. EGR valve works OK as applying vacuum to line when idling does make the engine run like crap. Returns to normal when pressure relased so no sticking. Possibility that valve still passes under high exhaust pressure ?? Any ideas?

 

PVPR system removed to simplify pressure feed to FPR and remove another potential problem.

 

 

Started to get a bit p'd off now so thought bugger it, will check the timing anyway. Both cars show 35° at 2000rpm! Got to thinking initially CAS is broken etc. initially adjusted Leighs to 15° which ended up with the CAS being wound right round - obviously looks wrong. From running was obviously retarded.

OK, try to figure out why timing is off. Measure MAF voltage at 2000rpm, stationary gives 1.43volts. Sure enough, TP calculated at 7, which accoding to the map should give - surprise surprise 35°. So basically timing is right for engine conditions (as measured).

 

Next measure MAF voltage at idle 1.07v, within spec of 0.8-1.5v as quoted in manual.

So basically it looks like what is going on is that the MAF isn't measuring all the air going into the engine at high revs, so it's leaning out and detting.

 

Thinking there are 3 possibilities:

1) EGR valve is passing a bit and so adding unmeterd oxygen / hot gas?

2) Air leak before turbos drawing air so it's not metering that amount. I think it would have to be a pretty big leak though.

3) MAF is a bit dodgy and is not reading the correct air flow.

 

Any ideas / comments greatly appreciated here guys both by me and leigh ...

 

Next step I suppose is try an new MAF :eek: or - try pinching the PCV hoses to see if idle is affected - apparently thats a way of identifying if it's an air leak.

Only other things I can think of that can cause detonation are:

 

1) A cylinder burning oil will essentially lower the octane rating of the fuel in that cylinder.

 

2) Carbon buildup on the top of the piston or elsewhere in the combustion chamber.

 

3) A sharp bit of casting in the combustion chamber.

Thanks for posting that John, both fingers and brain are only just about thawed out after today! Just to echo what Johns said, if anyone can shed any light on this it would be greatly appreciated as we've definately reached the tearing hair out with frustration stage!

 

Cheers,

 

Leigh.

Thanks for posting that John, both fingers and brain are only just about thawed out after today! Just to echo what Johns said, if anyone can shed any light on this it would be greatly appreciated as we've definately reached the tearing hair out with frustration stage!

 

Cheers,

 

Leigh.

 

If someone could lend you a conZult / Consult / DIY circuit (http://forum.ztechz.net) - then that should rule out the AFM / other sensors since you can perform real time logging of the sensors.

 

I thought for a moment it could be a dirty hot wire in the AFM, but that would cause you to run rich not lean, which is a bigger cause of det. Perhaps the components in the actual AFM circuit has gone way past its original tolerance? But unless somebody can find a company that can test AFMs then I guess you need to borrow a known good one from somewhere.

 

HTH

Simon.

If someone could lend you a conZult / Consult / DIY circuit (http://forum.ztechz.net) - then that should rule out the AFM / other sensors since you can perform real time logging of the sensors.

 

I thought for a moment it could be a dirty hot wire in the AFM, but that would cause you to run rich not lean, which is a bigger cause of det. Perhaps the components in the actual AFM circuit has gone way past its original tolerance? But unless somebody can find a company that can test AFMs then I guess you need to borrow a known good one from somewhere.

 

HTH

Simon.

 

I've got the MAF logged on my Profec E01 at the minute, which was how I saw it was on the wrong map point. Problem is still not sure whether it's dodgy sensor or leak!

Might try giving it a clean though, certainly can't harm at the minute :cry:

Knowing the history of MAF's on a zed, it is probably that!!

Knowing the history of MAF's on a zed, it is probably that!!

John I am just about to order a New MAF from the US once arrived you can use my old one if it helps mate

 

Ryan

Baggins, If you live local to John it would be better to let him strap the new one on and test it against that, then it takes a faulty MAF out of the equation!

John I am just about to order a New MAF from the US once arrived you can use my old one if it helps mate

 

Ryan

 

What price are they from courtesy Ryan?

What price are they from courtesy Ryan?

Well I do have a known good one aswell which we can try , John will check this afternoon when the US get there lazy arses out of bed but I think they are £300-£400 :cry:

Baggins, If you live local to John it would be better to let him strap the new one on

 

Mark don't encourage him :nono:

£300 - £400?????????????????????????????????????????

?????????????????????????????!???????????????????????

 

Jeez! :eek:

£300 - £400?????????????????????????????????????????

?????????????????????????????!???????????????????????

 

Jeez! :eek:

LOL not cheap little shrimp , thats why they sell for £150 second hand :rolleyes:

Better off going for an aftermarket air meter at that price!

Less of the little, Ryan :p

 

What aftermarket ones are made Mark?

Less of the little, Ryan :p

 

What aftermarket ones are made Mark?

HKS VPC but even these are no longer made and still sell for £500 + second hand , looks like a good bit of kit though , probably a bit OTT for my set up though , although I did consider this instead of a new MAF

I think HKS make one there are others but, I think the HKS is the most economically priced.

What price are they from courtesy Ryan?

John $546.99 + shipping and taxes :cry:

CZP, $390 + shipping ($45) & taxes!

Group buy?!

CZP, $390 + shipping ($45) & taxes!

Group buy?!

Gutted I bought mine last night :mad: :(

Bugger :eek:

Have you tried to simply clean the hotwire in your MAF? I read in an earlier post in this thread that a dirty hotwire should make it run rich and not lean, but to my best knowledge that is not the case, it will run lean with a dirty hotwire so clean it with some electrical spray-cleaner. The MAF is meassuring the air mass by sensing the flowing airs ability to tranfer heat from the wire, the more heat that is lost in the airflow the larger mass of air is flowing per time unit, but if the wire is dirty the dirt will isolate and not much heat will get tranfered to the flowing air so it will think the mass of the air flowing is lower than it really is and so the calculated Tp becomes lower that it should resulting in more advanced timing and less fuel...

 

/Niclas

Cheers Niclas, useful advice as ever.

I'll give it a shot. Andy P has been kind enough to lend me one to try, so if that fixes it I'll try cleaning mine and putting it back in.

Have you tried to simply clean the hotwire in your MAF? I read in an earlier post in this thread that a dirty hotwire should make it run rich and not lean, but to my best knowledge that is not the case, it will run lean with a dirty hotwire so clean it with some electrical spray-cleaner. The MAF is meassuring the air mass by sensing the flowing airs ability to tranfer heat from the wire, the more heat that is lost in the airflow the larger mass of air is flowing per time unit, but if the wire is dirty the dirt will isolate and not much heat will get tranfered to the flowing air so it will think the mass of the air flowing is lower than it really is and so the calculated Tp becomes lower that it should resulting in more advanced timing and less fuel...

 

/Niclas

 

I could be wrong but I thought the 300zx maf did not work on the hot wire principle!

No Mark you're wrong :p ;) LOL

Hello John

I dont know what on the car you have being looking at.

So i come with some suggiestion.

There is worth to look at the injector nossels, if one or more have bad connection it can lean out on a cylinder. Also measuring the resistance over them and the power supply. Is it on a particular rpm it detonating?