Engine will not rev

[Chris P]

I'm sorry that my first post has to be one with a problem.
I recently had fiited a Milltek cat back system which although did not improve performance that much, made a much nicer sound. However, after about two weeks the car started to run lumpily and would not rev cleanly above 2000rpm. I though that the CATS had gone as they were rattleing so took them off to find one had started to break up inside. I decided to remove all the internals of the CATS and put them back on.
The car started up and ran very roughly but then it cleared up, so i took it for a run. It was ok for 30 mins, although there was a hesitation at about 4000rpm but then it suddenly went back to the same way where it would not rev and i only managed to limp home.
As there is no restrictions in the CATS now, what other problems could it be ?.
If there is a fault on say the Lambda probe, would this cause the car to go into a limp home mode ?
Anyones help would be greatly appreciated.
I think that this should have gone in the exhaust section but i now beleive it is an engine problem.
PLEASE HELP!

[4WheelDrifter]

Have you checked for fault codes?

[porkkis]

Boost leak or ignition problem. As you seem to have an ABY the possibilities are plugs and ht leads.

Check the codes.

[Chris P]

I have not checked the fault codes yet as i need to get an LED. Will check that monday.
Boost is ok as it makes 1.1 bar (according to my guage anyway).
I am going to try and take the lambda probe out today and clean it to see if that clears it.
It just seems strange that it ran ok for a bit then came back again.
Why did i not buy that nice cheep reliable car instead !.

[merlin's S4]

Welcome to the forum! Is there any chance that part of the broken ceramics in the cats could have blocked the exhaust further down? Did you completely gut both cats?
Hope you sort it!

[4WheelDrifter]

Boost may look ok, but don't rule out a leak.
Where are you? There maybe someone nearby that can help.

[Chris P]

Yes i gutted both CATS and i checked that they were all clear so i do not think that there is anything else exhaust wise that could be causing the problem.
I have just taken the lambda probe out and just cleaned it off as i thought that if when the CATS were blocked it may have damaged this sensor somehow. It appears to be no different than others that i have seen.
Other than checking the fault codes, do you think the coils are the next step. Are these easy to check anf if so how do i do them ?.
I am in Sheffield by the way.
Thanks for all the advise.
Lets hope one of them solves it.

[4WheelDrifter]

You do need to check for codes really. Have you checked that no pipes have come lose or look damaged? It may be worth testing for leaks. Coils tend to produce a missfire, rather than a lack of revs.

[Chris P]

Thought i had found the problem then. Noticed that it was blowing condensation from one of the joints so tightend the bolts whilst it was running and it cleared up. Took the car out and a couple of miles from the house went back to poor running again. All the bolts seem tight and i cannot feel any blowing from the joints when it is running.
It will rev through the range but it sounds and feels very rough. Maybe it is not running on all cylinders. I cannot imagine gutting he cats will cause the engine to run this badly.

[4WheelDrifter]

No. It should run sweeter without the cats. It's difficult to test for boost leaks without a suitable pressure test kit and an air-line, to test your intake hoses. Just by looking at mine there appears to be no leak, but it in fact has a huge one. The test normally reveals the need for the Mark H intercooler mod, if not already done.

[Chris P]

Have just finished more tinkering. Have checked all the exhaust bolts and they are all tight. There was a slight leak on the clamped joint of the Milltek system but with use of some seaing paste these seem ok now.
My brother and i have just finished pressure testing the turbo system and that is holding ok.
We have also done the blink test as i have managed to find a 12v bulb to use instead of the L.E.D. This is giving the code 4411, which is number 1 fuel injector.
Has anyone had this problem and if so is it likely to be a blocked injector or electrical signal problem. I would assume that as it does sometimes clear itself and runs ok (even if it is only for a short while) that it is electical. What is the best way of testing this ?.
Other than the exhaust the car is standard, engine wise anyway. I would like to go for the chip next but for the time being just a running car would be nice.

[4WheelDrifter]

I had this problem quite a while ago. I had mine running on 3 cylinders sometimes. It turned out to be a loose connection on the injectors themselves. The plastic plugs had become very brittle, and had disintegrated. It's the purpley insert part inside the black plug body that goes.

[Chris P]

I really appreciate the help and advise you are giving 4wheelDrifter.
I have just taken the car out again. As usual it ran ok for the first couple of miles then started running badly. This time i took a multimeter with me and when it was running bad i checked the voltage at the injector connection. They all had about 13.5 volts.
It sure feels as though it is not running on more than one of the cylinders (even though the fault code only brings up no. 1) as the car has no power at all and struggles to get up our road. If it was only one cylinder i would assume that it would still run reasonably well.
I will go and check the actual connector itself as you have advised.

[4WheelDrifter]

It does sound like an electrical problem to me. Whether it's a sensor or a loose connection, I'm not sure. It sounds like the car runs fine until the ecu picks up on this intermittent fault, then goes into limp home mode. I seems you have chosen a quiet day on the forum to post. Maybe someone else will have a better idea.