LUMPY 4.5 RUNNING.

[Fudgenudger]

Hi Guys,

As the title says, I have a 99 4.5 Cerb and on slow running around town and on light throttle when the engine is warm or cold its quite lumpy, its not quite a misfire, well I dont think so anyway.
I have had the tappet service done and the throttle pots replaced and set up. I was quite good for a while but seems to have slowly come back.
I've heard that the plug leads are also prone to braking down due to the heat. Was wondering if anyone has any other sugestions.

Thanks.

[high52kojak]

Is it between 1600 and 2500 RPM by any chance?

[vroom]

Mine is certainly fluffy sounding or hesitant on part throttle in the 2-2.5k bracket

For what it is worth, I've just done a tune:

Throttle pots were miles out with adaptives at their limit

easily corrected, car drives better, but the above 'characteristic' is still there, but not as bad...

[pmessling]

I also raised this issue on here this week and was told from someone who had also experienced it that he changed the coils and all was well again. My coils arrived this morning, just waiting on the ht leads then i'll change the lot including spark plugs and hopefully that will see my good.

[brakedust]

Mine was doing the same last month, so I replaced both ignition coils, both throttle pots and all the leads.... Runs much better now (or would if my clutch hadn't just given up!)

[Fudgenudger]

Yea it seeems to be around that rev range but probably does not clear out until nearly 3000 RPM

high52kojak said:

Is it between 1600 and 2500 RPM by any chance?

[Fudgenudger]

Cheers guys, will replace the leads and possibly coils aswell, then see how it goes.
I've also heard that the throttle bodys themselves can wear out and need replacing, has anyone experieced this aswell ?

[Tanguero]

Plugs, coils, fuel filter and a carefull setup cured these symptoms for me yesterday.

[Poledriver]

Fudgenudger said:

Yea it seeems to be around that rev range but probably does not clear out until nearly 3000 RPM

high52kojak said:

Is it between 1600 and 2500 RPM by any chance?

Same here!

[pmessling]

Just waiting on my ht leads and carbon airboxes from ACT and will report back my findings. I found that someone had strangled on if the airboxes tumpets so I have brought the ACT carbon ones with back plates. I'm a sucker for anything carbon love the stuff.

[Fudgenudger]

Right, I have replaced the plugs, leads and boyh coils along with a recent tappet service, throttle pot replacement and set up and it is still lumpy between 1500-2700rpm.

I have not yet replaced the fuel filter but surly that cant't be the problem ?

When Top Cats Racing did the tappet service they did say that it was not the liveliest Cerb that they have driven, not slow by all means, just not the quickest by far.

The previous owner did have an an oil pump drive faliure a year and a bit ago as per invoice so I assume that the engine timing will have to be set up. If this was slightly out could it cause this problem. I also believe that the car is definatley as powerful or as quick as it should at least be.

I also have de-catted it aswell with one of ACT big bore systems.

Ant other ideas Guys ?

[Tanguero]

They are very sensitive to cam timing, but that should have been done when your valve clearances were set.

[high52kojak]

Has it ever been re-mapped? I doubt it as that rev range for lumpy running is pretty common. Its worth paying a bit for a proper mapping sesh, whether you want short induction or not.

[Fudgenudger]

I do not believe that it has been remapped, I know it definatly wasn't by the previous owner. I am currently thinking of getting it re-mapped and a short induction kit.

I was not aware that on the tappet service the timing should be checked. Do you not have to remove all the timing covers to adjust or reset the engine timing ?

[Tanguero]

Fudgenudger said:

I was not aware that on the tappet service the timing should be checked. Do you not have to remove all the timing covers to adjust or reset the engine timing ?

You have to remove the cam covers to check the valve clearances. You have to remove the cams themselves to adjust the valve clearances which of course loses timing. So yes, you would expect the timing to have been either checked or reset at the same time.

[Fudgenudger]

Of course you do , Stupid me. So I'd gess that the cam timing was correctly set up. Doh !

[jammy_basturd]

Though it is possible to mark the cams/cam pulleys before you remove the cams so that you can put the cams back in position after doing the shims, thus no needing to do the cam timing again. In fact the workshop manual tells you to do it this way!

However I'd still recommend checking it when shimming, and checking it now. But I agree with the others that this lumpy running between 1.5-3k rpm is "normal".

[high52kojak]

Get it to one of the mappers, they can check your cam timing and sort your map and induction etc, it might cost you a few quid but hey, its worth it.

Just be aware that your engine needs to be healthy before you start upping the power, you don't want it to chuck a rod out of the casing in protest. Has it been rebuilt, milage?

[Fudgenudger]

high52kojak said:

Get it to one of the mappers, they can check your cam timing and sort your map and induction etc, it might cost you a few quid but hey, its worth it.

Just be aware that your engine needs to be healthy before you start upping the power, you don't want it to chuck a rod out of the casing in protest. Has it been rebuilt, milage?

It has covered 42,000 miles. When the oil pump drive repair was carried out it had the main and big end bearings replaced so it has not had a full rebuild as such.

[Poledriver]

While replacing my (broken) diff mounting bracket I had my Cerb serviced.
During the service it was discovered that the MAP sensor was not connected! She's running a hell of a lot better now, still a little lumpy through the lower revs but the hesitation and mis-firing has gone and she pulls from 1500RPM!
Thanks to Geoff and Paul!