Hi All.

 

My car has started missfiring at higher rpm, anything above 4k. I have since cleaned the maf and ptu connecters, also reset the ecu. It got much better after cleaning the maf but still misfiring loads. I have read other posts that suggest the maf can cause this. Can the car be ran without the maf connected to test this thory or is it 100% needed?

The MAF is *vital* for calculating Air/Fuel ratio, and unplugging it will only make the engine run in an ultra-safe mode. What you want to do is try swapping it for a known good one, and see if the problem goes away.

 

Have you done a diagnostic?

 

Sounds like what-ever it is you should run the engine as little as possible...

 

Mark

AFAIK you will only be able to rev to 2.5k rpm with it disconnected. Someone will be along shortly to confirm.

AFAIK you will only be able to rev to 2.5k rpm with it disconnected. Someone will be along shortly to confirm.

 

I am pretty sure thats right as we had to disconnect ours on the way to jae as it got so wet and needed to dry out. We could only go about 40 and it was not a smooth ride!! lol

can be run with maf disconnected - ecu switches to limp home mode, so no damage will be caused... but this limits the revs to 2500 so it's unlikely to be the connectors. Not sure how mafs fil, but may be an idea to swap a good one in if someone's local to eiminate it??

 

Rich

think i will try swaping it for a working one, good to hear other people had simular problems with thiers in the wet!

 

I have read that sometimes they are ok when dried out, but sometimes its terminal.

Fail-safe operation;

 

http://www.300zx-twinturbo.com/cgi-bin/manual.cgi?list=efec&dir=&config=&refresh=&slide=33&cycle=off&scale=0&design=default&total=190

http://www.300zx-twinturbo.com/cgi-bin/manual.cgi?list=efec&dir=&config=&refresh=&direction=forward&scale=0&cycle=off&slide=34&design=default&total=190

think i will try swaping it for a working one, good to hear other people had simular problems with thiers in the wet!

 

I have read that sometimes they are ok when dried out, but sometimes its terminal.

 

We dried ours out under hand drier in mcdonalds and it got us all the way back to somerset fine.

its been hot for two days now since it rained and still the same, me thinks its poorly!

 

I will try another maf when i have dealt with my water leak! Grrr

Hmm... water leak you say?

 

Aren't I right in thinking that coolant temp is used in engine control? If so is you have a big air gap at your temp sensor this will be feeding incorrect temp data to the ECU and could mess up the engine handling... dunno :confused: Anyone agree with me??? :)

The coolant temp stays about 80c until it gets too low. There is air in the system as it sometimes jumps to 95 then cools back down to 80 once the aire has passed the sender.

 

The leak is in one of the heater pipes behind the glove box, can hear it hissing when I rev the car!

The leak is in one of the heater pipes behind the glove box, can hear it hissing when I rev the car!

 

That'll be the heater matrix that's gone then :cry:

Dash has to come out to change it - not an easy job.

 

I'd prepare for wet feet when it finally lets go!

Changed heater matrix myself a couple of years ago. Nasty job but somehow enjoyed getting to know more about the car. Took me a week (winter nights, on driveway after work - not a mechanic) and the new matrix only lasted 6 months! Bugger! Sold the car not long after! If it is your matrix gone, good luck mate.

Er thanks.. i Think!

If you start at about 0800 you can have the dash out and Matrix replaced by tea time.

 

I'd never done it before and it still only took me till tea time. I had to get it done before my mate shut his garage. I also fed new wiring loom through bulkhead. Thats it on the drivers seat. The rustty bit is what happens when the matrix is leaking for a while. All sorted now though and Long life coolant stops the electrostactic build up in your water system that causes it.

I totally agree with Mark W, like I said before the coolant is mega important to these cars. My car ran rough when it had air in the cooling system and my mate’s car did too (that’s Marcz32). Got all the air out and give the car a good run, ECU re-learnt the mix and temp, now it’s spot on again.

Ok ta well my cooling system is priority 1 as cant drive it with the leak as its getting worse. I'll swap test the maf if the problem is not cured when i have the cooling system sorted and reset the ecu properly. Is the heater matrix in the middle of the dash or on the passenger side behind the glove box?

to markzx, can you get to the heater without going quite as far as you did in that pic?

to markzx, can you get to the heater without going quite as far as you did in that pic?

 

Unfortunately not, because you need to clear everything out of the way on drivers side so you can dismantle thr control arms on the Matrix inlet and so you can feed the new matrix inlet and outlet pipes through the bulkhead.

 

The pasenger side has to be dismantle right that far so you can remove the aircon matrix and controls so you cna side the Heater Matrix out of its housing. Also to slide the new one back in.

 

While you on with this I would suggest replacing your other water pipes and doing a Plenum byepass and bang on a new water pump. Then use some proper coolant and at least 70 percent coolant.

 

Sorry but it sound s like its that time.

Gutted, the water pump and stat, all the front pipes were changed 18 months ago.

Just spend loads on my clutch and brakes as well! Its going back to the garage tomorrow as the exhaust is ratteling since they put it back on, I'll get them to check all the water pipes at the rear and underneith the engine again but they couldnt find a leak last time. The fact that my glove box is hissing and the carpet a bit wet sort of confirms it tho, bugger!

Gutted, the water pump and stat, all the front pipes were changed 18 months ago.

Just spend loads on my clutch and brakes as well! Its going back to the garage tomorrow as the exhaust is ratteling since they put it back on, I'll get them to check all the water pipes at the rear and underneith the engine again but they couldnt find a leak last time. The fact that my glove box is hissing and the carpet a bit wet sort of confirms it tho, bugger!

 

Sorry to say this, but when the Matrix goes its down to corrosion and if you change all the rubber pipes with silicone you can check the metal pipes their conected to. Often the whole system gets corroded because cheep coolants and not enough coolant allow a electro meanetic static field to build up in the water (hence grounding kits Help) and this corrodes the metals. Long life coolant (the pink Glycol based stuff) provents it and helps cool your engine better. They should have 70percent glycol to 30 percent water aswell.

 

Most garages have premixed drums of cheep stuff and it is mixed 30 percent usually achohol based to 70 percent water. Not good for a Zed.

That'll explain all the rust in my coolant when i got the car! I have flushed it and use 50/50 mix of coolant so its clear and blue now. Looks like the damage had already been done, I'll get my spanners out!

to markzx, can you get to the heater without going quite as far as you did in that pic?

 

no, you dont need to remove the dash to replace heater matrix, but it is a fiddly and annoying job.

 

I've seen it done in 3 hours a few times on an Auto. With a manual you need to remove the clutch pedal and booster and takes a little longer.

no, you dont need to remove the dash to replace heater matrix, but it is a fiddly and annoying job.

 

I've seen it done in 3 hours a few times on an Auto. With a manual you need to remove the clutch pedal and booster and takes a little longer.

 

I didn't remove my clutch peddle??? + I've heard of it being done with the top of the dash in place, but having done it myself I'd still go for the removel job as you can get at the heart of it. 3 hours!!! I carn't believe that.

There is a link on the a-z of overheating page to a walkthrough on how to remove the heater matix without removing the dash but its a dead link Grr!

 

The hissing/running water noise is coming from the passanger side behind the glove box anyway, i thought that is where the matrix is?

You can just byass the matrix for now and get the other bits sorted? Means you'll be able to enjoy the rest of the good weather and fix it over the winter...

 

Rich