At my wits' end with this bloody ZX - intake boost results

Oscar · Post by **Oscar** » Mon Dec 05, 2011 8:03 am

Fuel consumption is now 33mpg. I might as well be driving a van.

I've changed filters, intercooler (old one was leaking), injectors, (cambelt, water pump and drivebelt along the way too). I've also replaced a binding brake caliper.

Nothing works. Fuel consumption is still outrageous. I accept it's a larger engine in a heavier car than the BX, and it's got winter tyres on and a bit of clutter in the boot, but still...

Am I now looking at adjusting fuel pump? injection timing? Turbo? Please folks, constructive suggestions welcomed. It's a diesel, btw.

I'm seriously thinking about buying a Volvo.

Oscar

Way2go · Post by **Way2go** » Mon Dec 05, 2011 2:23 pm

Oscar wrote: I'm seriously thinking about buying a Volvo.
Oscar

Not missing a BX as much as you said then?

MULLEY · Post by **MULLEY** » Mon Dec 05, 2011 8:03 pm

Hmm, difficult to say as most of the things that you mentioned which have been replaced would be on my list of things to check/replace.

Does the car drive normally with the exception of the shite fuel economy? If not, can you describe what it feels like now, compared to when it was working properly? Does your car have an ECU? If so has this been checked? Don't suppose you've got a CAT as well? Has that been checked?

Discoil · Post by **Discoil** » Mon Dec 05, 2011 8:10 pm

What does the smoke / mot test show up as ?

sdelasal · Post by **sdelasal** » Mon Dec 05, 2011 8:25 pm

hi oscar - Some possibilities would be - brakes binding, engine compression really really bad (i.e. hard to start even with good glow plugs), pump timing or pump fueling.

There should be a small connecting pipe between the intake manifold and the injection pump - what this does is increase pump fuel rate based on intake boost pressure. If you disconnect it, the car will drive as if it has no turbo. Try it & see what mpg you get. If it's a lot better then either your boot is too heavy or the pump is over-fueling. If no difference, then look at pump timing. Steve

Oscar · Post by **Oscar** » Mon Dec 05, 2011 8:46 pm

Steve, top man, thank you. I'll try that. I think it must be the pump at this stage. Performance is quite pokey now I've done all the other issues, but fuel consumption is really ropey eg yesterday I filled it, went 95 miles to Gatwick and back on the open motorway at a nice 68-75 mph with no idling or creeping in heavy traffic - 38mpg. The BX used to do 55mpg in those conditions. I shall disconnect the pipe forthwith.

Oscar

Dollywobbler · Post by **Dollywobbler** » Mon Dec 05, 2011 8:48 pm

Presumably you've checked for fuel leaks front to rear?

Oscar · Post by **Oscar** » Mon Dec 05, 2011 8:50 pm

Dolly also a good point. I had a good scout on my hands and knees yesterday but it may be worth getting it onto Phil's ramps. I'll call him tomorrow and see if he has a ramp free.

sdelasal · Post by **sdelasal** » Mon Dec 05, 2011 9:13 pm

The leak suggestion is a very good one - look also for leaks around the injection pump that only become apparent with the engine is running i.e. with the pump pumping... in this case, you'd see diesel dripping off of the sump as it runs down the block.
Other simple possibilities
- someone is helping themselves to your fuel when you're not watching!
- your odometer is under-reading i.e. your are travelling more miles than it is recording - i've seen ones which stop working when they get warm for example!.

Oscar · Post by **Oscar** » Mon Dec 05, 2011 9:56 pm

I'll check for running leaks too.

The odomoter is fine - the distance to Gatwick and back was correct, I've done it every 2 months for the last 5 years....

Oscar · Post by **Oscar** » Sun Dec 11, 2011 3:29 pm

Right. Following Steve's advice (thank you Steve) I disconnected the intake boost from the intercooler.

Prior to that I'd filled the tank to the first cut-out and done 10 miles. This morning after disconnecting the boost, I did a further 90 miles to Gatwick and back - same load, road, and driving conditions as last weekend's run, when I got 38mpg.

When I returned I had done 100.7 miles since the last fill, so I pulled in to the local station and filled it again. I put 7.36 litres in to the first auto-cutoff and as I thought that perhaps it had cut out prematurely, I squeezed another 0.94 litres in, to reach 8.3 litres. 100.7/7.36 gives 13.6 mpl or 61.5mpg (!!!!

). 100.7/8.3 gives 12.13 mpl or 54.59 mpg.

This wasn't a lab test but it was pretty close to one, the only major difference was the road was wetter than last week and the temperature was a little cooler. If anything these conditions would make fuel consumption worse slightly. Performance wasn't badly affected - there were a couple of spots where I expected the turbo boost and didn't get it but in general it was as fast and as responsive as I wanted.

So, pretty conclusive really - the pump is over-fuelling as Steve says. I shall call our local fuel injection specialist - Rochester City Diesel, 01634 813 305 [/shameless plug] and ask what he thinks, but I'm very tempted just to leave the boost disconnected. Are there any disadvantages to this?

sdelasal · Post by **sdelasal** » Sun Dec 11, 2011 3:49 pm

The boost fuelling adjustment is something that some people will fiddle with to 'get more power' - for example - http://www.fourwd.org.uk/bosch_ve.html So that could be a reason.

The only disadvantage to leaving it dis-connected will be loss of performance - acceleration and ability to hold higher speeds. You might want to seal the end of the pipe to stop dirt getting in.

Oscar · Post by **Oscar** » Mon Jan 02, 2012 5:36 pm

Well, the early results from my last post didn't hold up - I didn't really expect them to. A longer trial up to 300 miles gave me fuel consumption of 43mpg, mixed, but mostly easy motorway, driving.

So I've had fun this morning adjusting the fuel pump as per the link you sent, Steve, once again my sincere thanks. A couple of minor issues aside (e.g. forgetting to remove the plastic bag from the alternator and getting the shock of my life as it got sucked into the alternator pulley as I was giving it a spin....) it was pretty straightforward. I adjusted the off-boost fuel delivery, initially the wrong way, just for kicks, to see what sort of smoke I could generate - answer: lots! And then the right way which got rid of smoke entirely. Then I adjusted the maximum fuel screw, and reconnected the turbo boost pipe. The car is now a little slower starting off, it feels like it's got a turbo in the mid range, but it runs out of legs somewhere around 85mpg and you can feel this happening from about 75mpg. Still pokey enough and fast enough for anything we'd want to do, so I shall run it like this for a tankful and see what sort of mpg we get. Watch this space.

MULLEY · Post by **MULLEY** » Mon Jan 02, 2012 6:11 pm

Glad you've managed to have a fiddle with things, lets hope it sorts out your poor fuel consumption figures. I would expect your ZX to be averaging mid 40's in normal driving & if you start hipermiling then into the 50's, so fingers crossed

With the price of fuel these day's, if its not even getting 40mpg, then its time to get rid unless you do minimal miles.

Philip Chidlow · Post by **Philip Chidlow** » Mon Jan 02, 2012 9:04 pm

Get rid. There are so, so many cheap alternatives at the moment. Please remember the old horse, dead and flogging adage.

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At my wits' end with this bloody ZX - intake boost results

At my wits' end with this bloody ZX - intake boost results

Re: At my wits' end with this bloody ZX