MY V8 RUNNING RUFF plus a wierd air flow problem???

[disco-v8]

ok just been messing with my V8 today to see why its not running right....

well just before the videos i made i took out all the plugs and did a compresion test and cleaned all the plugs up, look at some of these pressures  

all in BAR!!!! (nice one mick)

10.5........(8 7)........10.5
10.5........(6 5)........10.5
11...........(4 3)........10.5
10.3........(2 1)..........11

not bad for an engine with a compression ratio of 9.35  that what you get buying recon heads that have been shimmed, the compression goes up

well fair enough i started it from cold and it may have been running at full temp but when i usualy drive it it gets hotter than this so some of the temperature reads are lower than i recon they do get, but doesnt matter cuz it still wasnt running right.... the sound on the video wasnt as good as i was hoping but just before i mess with the fuel pressure you should hear it back fire through the air box, and just after it does it aswell  that cant be right!!!!!

(DAMB VIDEO IS TO LARGE TO UPLOAD ON YOU TUBE WILL TRY SOMETHING LATER)

ok here is another video which realy confuses me totaly, i thought while the engine was ruuning id take the lid off my airbox to see if there was any blockagies, but asoon as i started to take the lid of the revs started to die  at first i thought that i might of been bending the inlet hose and blocking air flow but no this wasnt the problem, i tryed squeezing it to prove it.....
every car i have had including this V8, when i take the air box off the engine usualy picks up abit as the air flow isnt restricted, but this does the exsact opisit!!!! the sound file is abit hard to hear as all you can hear is the suck of the air, so i filmed the power stearing pully spinning, and asoon as i lift the air box lid the wheel slows down!!!!

http://uk.youtube.com/watch?v=DTAYq2lDmsk

can anyone explain this to me cuz im lost

[Skibum346]

If it's not dying because air is being blocked.. I'd suggest it is because the fuel isn't there...

If the mixture is thin already... then you allow more air in by opening the airbox... the mixture is even thinner....?

TBH I'm guessing.

Only other thought is if it's an efi, the ECU is either duff or getting screwed readings from the Lambdas or other such sensors?

Good luck matey.

Skibum

[Evilgoat]

MAF/Airflow sensor a bit dickey?

[disco-v8]

MAF/Airflow sensor a bit dickey?

my thoughts exsactly, still hoping its not this as it only about 5months old and only done afew 100miles on it!!!!! but if it is this y is it trying to stall when more air gets to it?????


so whats the best way of testing this then???? and remember mine is the airflow meter off a gems engine 4.0/4.6

[Evilgoat]

MAF/Airflow sensor a bit dickey?

my thoughts exsactly, still hoping its not this as it only about 5months old and only done afew 100miles on it!!!!! but if it is this y is it trying to stall when more air gets to it?????


so whats the best way of testing this then???? and remember mine is the airflow meter off a gems engine 4.0/4.6

I'm not sure, only experience i have is with MAP sensors which are very different. I'm sure someone will be along, iirc its a Lucas Hotwire sensor but it may be different between systems. The increase in airflow may not be sensed and hence the engine is suddenly underfueled drastically.

Most ECUs have a LOS (Limited Operation Strategy) that allows you to limp home, maybe you are stuck in this mode if the Rover ECU has it.

[skip]

That's just how my disco runs all the time on petrol, yet it's not too bad on gas.

both sytems use the lamda so I can only guess it's the air flow meters.

I'll be watching with interest to see how you get on.

[Thrasher]

The Rover ECU on that engine brings up a check engine if a sensor is out of range. There is no "limp mode", it just substitutes for a known good map.

[remmy7]

Hi there,

I am not the most the most experienced V8 owner on this forum but I have had to replace around 4 MAF meters. I run a 4.0 V8 and have found that whilst it will run with the MAF disconnected allowing the Lambda sensors to do all the work, it will run very rough and perhaps stall if I do anything with the Air flow or MAF whilst its running. It may sound silly but try running it with or without the air box sealed but switch of between attempts, it could just be that the ECU is getting confused. I may be wrong but could it be if the MAF is goosed then the ECU isnt computing the airflow quick enough from the data from the Lambda sensors.

To be honest I am only guessing as I am starting to believe that a witch docter would be better placed to get my V8 running smoothly.

Regards Remmy7

[solihull-mick]

Are you sure the figures you have are right? cos if your engine is running with 10.5 psi compression your doing well, 100psi is ok but a tip top engine should be more the 130 to 150 psi mark, do you mean bar?

And dont get confused with the 9.35:1 thats the compression ratio not what you get from the plug hole with a gauge, :)

[disco-v8]

Are you sure the figures you have are right? cos if your engine is running with 10.5 psi compression your doing well, 100psi is ok but a tip top engine should be more the 130 to 150 psi mark, do you mean bar?

And dont get confused with the 9.35:1 thats the compression ratio not what you get from the plug hole with a gauge, :)

nice one there mick, made my self look abit a an arse then  :lol:  yep i ment bar


and you no what i mean by the 9.35 ratio, when you do a compression test it should come up at 9.35BAR as it usued to do before i reconned the engine

[smurf]

To check if its the Airflow meter just run with it connected, then run with it disconnected.
If it runs poor & miss fires etc with it connected, then runs ok disconnected then your Airflow meter is sending dodgy information.
Yes I know that disconnected it will run with a lack of power but it will run smooth because you have removed the faulty component.
If it still runs crap with it disconnected then its not the airflow meter.
The ECU uses a default mode if you disconnect a component.

Hope this info is useful.

[solihull-mick]

Are you sure the figures you have are right? cos if your engine is running with 10.5 psi compression your doing well, 100psi is ok but a tip top engine should be more the 130 to 150 psi mark, do you mean bar?

And dont get confused with the 9.35:1 thats the compression ratio not what you get from the plug hole with a gauge, :)

nice one there mick, made my self look abit a an arse then  :lol:  yep i ment bar


and you no what i mean by the 9.35 ratio, when you do a compression test it should come up at 9.35BAR as it usued to do before i reconned the engine

The compresion ratio of 9.35:1 in not what you should get at each cylinder, thats the ratio that the cylinder compresses the air in relation to the cylinder size, do a google on it it will become clear, you can have a really low compresion ratio engine of say 7.2:1 that was my cosworth, but compression reading was  155 psi at the plug hole, hope this makes sense :D

[Range Rover Blues]

I get around 200 PSI from a good V8, don't know that that is in bar though.

Anyway, I thought the MAF sensor looked odd, till you pointed out it's from a GEMS stystem.  Have you tried putting the correct one back in?

It does strike me as a MAF problem though, have you tried running with it disconnected? my LSE will run fine with no MAF because it has Lambdas, these are the primary input for air/fuel ratio when fitted  Blue doesn't have Lambdas and wil  not run without the MAF sensor, well not that well at least.

[solihull-mick]

I get around 200 PSI from a good V8, don't know that that is in bar though.

I would hope your not getting 200 bar compression, thats the same a as an oxygen bottle full!  200 psi sounds right mate, and a very good 200 at that,  :D

[Range Rover Blues]

I get around 200 PSI from a good V8, don't know that that is in bar though.

I would hope your not getting 200 bar compression, thats the same a as an oxygen bottle full!  200 psi sounds right mate, and a very good 200 at that,  :D

That's my typing :roll:  should have read what that is in bar.

Anyhoo, that was after a head skim and valve lap, arond 205PSI which is probably about as high as you might want, I did have one that ran up to 215 but that caused me problems :?

IIRC they need to be better than 165 PSi and within a few PSi of each other.

[Ja1983]

replace with some nice big SU`s.... whoe need sfuel economy?! :lol:

with the compression been a little skewe wiff (10.3 > 11 BAR) does the missing correspond with the hi/lo cylinder...  ie, could there be a slack valve seal or maybe something which could be throwing the lambda off?

..i know very little about V8`s and ecu`s seem to be very troublesome, hence the opening line, maybe a bit of a bad connection on the Air flow meter, that is disturbed when you opened the airbox?

hope you solve it soon! :D

[Range Rover Blues]

It was the earlier flapper type EFi that gained a bad reputation, the hot wire is a far more robust system with some degree of sensor redundancy, plus simple plug in diganostic, not that it always tells you what's going on.

[Rossko]

Anyway, I thought the MAF sensor looked odd, till you pointed out it's from a GEMS stystem.  Have you tried putting the correct one back in?

There's a big hint for you there.  If this engine is running a 14CUX ECU, as a 3.9 should, you should have either a 3AM or 5AM boxy looking airflow meter.  That is the same as a 4.2 - but quite different to a 4.6 one, which is what you appear to have fitted in the video!

I don't think you can directly swap 3AM and 5AM units, although they both look alike and both work with a 14CUX - the 14CUX comes in different versions to suit.

[disco-v8]

Anyway, I thought the MAF sensor looked odd, till you pointed out it's from a GEMS stystem.  Have you tried putting the correct one back in?

There's a big hint for you there.  If this engine is running a 14CUX ECU, as a 3.9 should, you should have either a 3AM or 5AM boxy looking airflow meter.  That is the same as a 4.2 - but quite different to a 4.6 one, which is what you appear to have fitted in the video!

I don't think you can directly swap 3AM and 5AM units, although they both look alike and both work with a 14CUX - the 14CUX comes in different versions to suit.

sorry will have to totaly disagree with you on that one, the gems 20AM AFM is a comon swop for big V8's as the air flow is ment to be something like 20% better as it has a larger through, the air flow meter sorts all the tricky stuff out and send the same sort of reading back to the ECU, then the ECU decieds what to do.......
the only difference is that the 3/5AM AFM have 4 wires and the 20AM has only 3..... but the extra wire is for a built in adjuster pot to calibrate the CO at idle on the 3/5AM which is built into the AFM , but the 20AM doesnt have this so you have to wire it up your self and calibrate it to 1.8V for a CAT and 1.5V for none CAT...... i used the old pot out of my old AFM and wired it up that way....

[jaysastud]

not sure if it helps,everyone is looking at the technical stuff!but i hve had probs a litle like this before on sports cars,the prob was the air flow goes up and so should the fuel,but ive had the problemht the fuel pump isnt good enough to cope,all goes odd,ecu cant cope and it all just goes belly up!basically too much air and not enough fuel.not sure if that helps as havent checked the vidsas pc gone all odd,but it may be about the same problem?if not no idea sorry!