Zx 16v Lack Of Power 3-4k Rpm

[gav_mi16 0]

Had this ZX a few months now and I love the handling.

 

Anyway, the engine is very strong after 4k rpm but there are two main issues;

 

Hesitates when given some throttle on idle

Painfully slow acceleration between 3 to 4k rpm (as soon as it passes 4 it pulls like a train), almost as if you are pulling a tractor behind and then the rope snaps when you reach 4k

 

Very good compression and pretty even, and i've tried a spare ecu also

 

Any ideas chaps?

[Anthony 1,000]

Is the ACAV working properly? It's a common fault on those engines (XU10J4 - same as found in 405 2.0 Mi16 and 306 S16's) and makes the engine flat as a pancake at low revs when it's broken

[gav_mi16 0]

As far as I can tell yes, a couple of things were changed. I'm not very familair with the system though and might have missed a hose or two when checking.

 

Will an ACAV fault be that dramatic?

 

I'll search for a guide and check again.

[James_R 3]

In short, yes very much so.

 

Check both sides on the inlet manifold work and the throttle is opened from idle (look at the rods coming out the bottom of the diaphrams for movement)

 

It can mostly be the solenoid packing up which is located on top of the gearbox.

[gav_mi16 0]

OK, thanks for the help chaps, I will have to dig a little deeper then, it does help that i have a complete spare engine to try things, I had bought it over a year ago just for the block and head as a spare for my Pug, as i converted it to a 2.0Mi with all 1.9Mi wiring and manifolds after blowing up 3 1.9's I went down the 2.0 and never looked back!

[welshpug 1,626]

As mentioned, check that the solenoid switches (at circa 1800 RPM IIRC) and opens the butterflies.

 

Having said that, do bear in mind that it might not actually be that bad low down, but feels like it because its soooo good above 4k....

[gav_mi16 0]

My brother has dropped off a load of new bits for me but i'm still trying to get my head round this ACAV system. I've searched for a schematic but havnt found one, anyone have one?

[VisaGTi16v 1]

Look for the two round mushroom shaped things shown in the pic below. Note the small thin metal rods coming out of the bottom of them. Watch one at a time and rev the engine slightly, just as the revs pick up the rods should be sucked upwards which is done by a vacuum. Make sure both are working. Its common for them not to. If they dont then it will be getting far too much air at lower revs which its not mapped for and hence will be down on power, this is why when you fit a gti6 manifold to them, yes you get more power top end but you lose the initial low down grunt.

 

If you increase the revs to just over 5k the rods drop back down as it opens up the 2nd inlet tract. Its common for them to either break or there to be a leak in the pipes somewhere, be careful where the pipe pushes onto the top of them as they are so fragile. When it goes back to idle they also drop back down

 

Welshpug: Although the Haynes BOL says they act at 1800rpm, every zx 16v ive seen they moved right after idle and didnt return until 5k

 

Edited June 2, 2009 by VisaGTi16v

[gav_mi16 0]

Thanks for the pic, so down at idle, up between 1800 to 5080 then down again.

What i mean about a schematic is like an electrical diagram so i can trace all the hoses pumps servos and check it all over. So far i've found a little unit front o/s, unit back n/s, something on g/box, something bolted to the head and pipes going to ecu.

 

I feel like a baby learning all over again, I know my xu9j4 loom inside out.

 

Oh, by the way the solenoids don't move at all, stuck in the down position, I can hear a loud sucking noise on idle from the afm area

Edited June 2, 2009 by gav_mi16

[welshpug 1,626]

there is no AFM....

[gav_mi16 0]

there is no AFM....

 

bah, you know what i mean

[welshpug 1,626]

do I? I have one outside and can't imagine what you would refer to as an AFM

[James_R 3]

throttle body area??

 

Just look over the vac hosing, you'll be looking for vac line to solenoid then it goes on a T to the two diaphrams, also check the 4 way valve thingy on the Vac pump, if this is knackered then you'll get a Fail of the ACAV system.

[gav_mi16 0]

One of the diaphrams wasnt working, the vaccum suction was leaking through it so the other didn't work either. Replaced that one off the spare engine and the system worked fine on the drive and down to the first junction, it felt good. After that I was doubting if there was any real difference. Got petrol, came back, checked over and it's not working again this time no vaccum, diaphrams are working.

 

There are some differences to my spare engine, i don't have that big disk thing. The spare is believed to be a 405.

 

405 spare engine

 

My ZX engine with problems

 

I'll check the solenoid when i have some time. Something has obviously gone because it has had to do some work for a change

Edited June 4, 2009 by gav_mi16

[welshpug 1,626]

is your ecu/battery box just removed to work on it?

 

I don't think there's a vacuum accumulator on the zx because the ZX uses a vacuum pump and the 405 doesn't.

Edited June 4, 2009 by welshpug

[gav_mi16 0]

is your ecu/battery box just removed to work on it?

 

Yep, battery box removed to work on it otherwise i can't see bugger all down there! I was looking to see if the components are the same. As I said before i'm new to the ACAV system having always just thrown it out when fitting the engine to my pug.

 

I don't think there's a vacuum accumulator on the zx because the ZX uses a vacuum pump and the 405 doesn't.

 

ah, so that's the different, thanks for that. Anyway, can't see the same solenoid on the 405 engine, so i'll source one. It's getting vaccum, but not "switching", havn't checked the voltage yet as my multimeter is pooped.

[welshpug 1,626]

solenoid is definitely on the 405 engine, had to change it on mine, its normally bolted to the plate above the accumulator in your picture where the vacuum pipe sits disconnected.

 

a side repeater bulb holder borrowed from the scrapyard is enough to test that the ecu is sending the switching signal

Edited June 4, 2009 by welshpug

[gav_mi16 0]

It must have been pinched by someone then.

 

What's the voltage for the solenoid? 5v or 12v?

[welshpug 1,626]

now you mention it I don't know for certain and can't find any reference to it, I do know you would most likely find it in autodata's ecu pinout and function listings

 

it did light up a 12v bulb IIRC.

[Tom Fenton 1,526]

5v is usually just for sensors, something like a solenoid valve I would expect to be 12v, but don't take that as gospel.