Lack of ommph... by Justin

Apologies for the tail of woe...

Over the last couple of years I have had a problem with my mk 1 ZT, it has a intermitant problem which manifests itself with the car suffering a lack of power and the engine sounding much noiser than normal, the odd thing is that after 2/3 weeks of this it will suddenly improve again, loads of torque, smooth acceleration and bags of power.

The car has been to a x-part MG specialist who have put the car on the T4 (Testbook version 4.Computer Diagnostic System), no fault codes were found, and the injector readings were correct, apparently the only thing they could do was to update the ECU (Engine Control Unit) map to its latest version. I had always thought it was a MAF (Mass Air Flow Sensor) issue but having used both a pierburgh MAF (with the synergy) and a replacement Bosch there was no real improvement, disconnecting the MAF and synergy does not make any differance, the in-tank pump has been replaced and the HP injector pump which failed has also been done, but again no improvement. I have also tried several bottles of injector cleaner. Mileage is 128,000ish

The symptoms are:

Reduced torque below 2000 rpm
Reluctance to pull past 3000rpm
Increased engine noise (sounds harsh and unrefined)
No smoke or anything
Both fuel pumps are working (based on them making a noise)
HP pump is only 3000 miles old
The car still maintains its road speed/engine speed (ie 70mph is always 2200rpm regardless of the problem) which suggests its not a clutch issue.

If anyone has any suggestions about what this could be or can suggest a specialist garage near the south coast I would appriciate it as it has stumped the garage and me.

I posted a simular thread on teh other side a few months ago but never got a reply....



Posted 22 Jul 2010, 12:25 #1 

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this does sound a strange one.has the connection for the fuel pressure senor on the end of the fuel rail been check?if this was the problem l would have thought a fault would be logged when you got it put on the its free to check l would have a look.lm sure someone with more knowledgethan me will be along shortly


Posted 22 Jul 2010, 15:41 #2 

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Sorry to hear of your problems,
a quick couple of checks to make are:

Blocked EGR (Exhaust Gas Recirculation Valve)
Blocked or old PCV (Positive Crankcase Ventilation Valve)
Old blocked Air Filter

"O" rings swelled and pipe out and need replacing, quite common on the diesels, easiest to take off front bumper to fit though, but normally you do get some smoke.
Jules has these is stock.

Although your symptoms are that of a failed MAF as you say that has been checked and leaking Injectors.

"My lovely car now sold onto a very happy new owner.
I still love this marque and I will still be around, preferred selling to breaking, as a great runner and performer"

Posted 22 Jul 2010, 16:42 #3 

Hi JonJon,

I have tried to clean the contacts on the Fuel rail pressure sensor with switch cleaner, sometimes it makes a slight differance. Are these known to play up? I think a replacement is around £80.00 which is ok if this is the cause but there is no fault code logged.


PCV was changed to one of the new BMW ones about 15,000 miles ago, although this was only the insert and not the housing, does this need to be replaced also?

Air filter has been changed to a pipercross one and it fairly new.

EGR has had a clean out but each time its not that clogged.

I have fitted the replacement ('jules') O rings but 3 weeks ago I had to reposition the lower one and this gave some improvement, unless this has slipped again, although there is no black smoke even with the synergy 2 on setting 10.

In terms of the overall impact on drivability its not like the cannot be driven but its seems to be 25% off what it should, which is a pain when you need the engine torque that you get used to with a CDTi.

Thanks for the suggestions, it could even be the injectors (I don't have much faith in the garage, having a T4 is not the same as knowing how to use it!), the problem is that I do not really know what im doing, can anyone suggest a knowledgable garage round west sussex?


Posted 23 Jul 2010, 14:33 #4 

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hi justin
the times l remember reading about the senor having problems is when a synergy has been fitted and the sensor/connector has some how been said though a fault should have been logged.when l was having a small problem a helpfull chap on here called russ told me to clean the boost sensor incase it was getting blocked.this might not help you with your problem but its worth checking.

JDC has covered anything else l can think of


Posted 23 Jul 2010, 16:26 #5 

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Hi Justin regarding the PCV.

I believe the casing needs replacing every 90k miles. The opposite side to the filter has a diaphragm which will wear out.

I have just ordered the complete unit for mine. Is a LR dealership on eBay that does them at a reasonable price.

View eBay item 320422225388

Member No. 143
Mods so far: LED sidelights, interior lights and number plate lamps, Rover Xenon Headlights, Kenlowe Fan, Synergy 2 and EGR Bypass

Posted 23 Jul 2010, 18:25 #6 

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have you tryed switching the synergy to other settings ?.

Posted 23 Jul 2010, 19:36 #7 

Thanks to everyone for your replies!

I changed the PCV unit and have used the filter that came with it to replace the later 'fit and forget' BMW part, inpatience got the better of me so it cost £50.00 from a x-part dealer. One of the symptoms that I omited to list was that the engine sounded like it was'nt breathing right on idle and this has been cured. I have also changed the Synergy setting to 10 and I used some switch cleaning lubricant on the fuel rail pressure sensor.

The result..........

My MG is back! There is a definate improvement in the low down torque with the engine pullling from lower down the rev range (arond 1300 rpm) and it sounds much smoother, the power delivery is much more progressive as well.

Im hopeing that it will stay this way and will update in a couple of weeks.

Previous attempts to resolve this used to involve increasing the MAF compensation on the synergy which did not really improve much (some improvement in low revs but overfuelling at highier revs) and made the car smoke, I suppose the lesson is that thr MAF is not always the culprit.

Thanks again to everyone who took the time to reply.

Posted 26 Jul 2010, 07:38 #8 

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thats good to hear.l will keep my fingers cross for you


Posted 26 Jul 2010, 11:08 #9 

Thanks Jon!

Posted 26 Jul 2010, 11:31 #10 

Update - 3 days commuting to London (500 miles) and things seem to be holding up, I do seem to suffer a small drop off when getting up to speed again after sitting in traffic but it is much better.

On to the next job now - the cooling fan.....


Posted 29 Jul 2010, 12:41 #11