Running slightly rough after fitting 4-2-1 system - help?

[paulous]

I recently fitted a second-hand Milltek 4-2-1 system to my 1.7 Puma, it’s the full system and I had a sportcat custom made (200 cell) so that part is new. Since having it fitted I’ve noticed a strange issue. Everything runs fine on tickover and when accelerating (yes it’s slightly more powerful than before, which is what I expected) but when cruising, particularly noticeable on the motorway, there’s a very slight hesitance in the engine every 10 seconds or so. It’s quite hard to explain. On the motorway it’s as if you’re driving in to a gusty head wind, just every 10 seconds or so there’s a very slight dip in power just enough to make it noticeable. It’s also noticeable when allowing the car to come down on the revs - if I lift off and just let the revs comes down it’s not smooth any more like it used to be, there’s a dip every 10 seconds or so which makes the car lurch forward very very slightly. It’s really weird, it’s just not running as smoothly any more.

I also recently fitted a FRP mod’d airbox (but it ran quite happily just with that for a few weeks before fitting the milltek) and my ECU has also got Pumaspeed’s remap (DIVE ECU). So apart from the 4-2-1, FRP airbox and ECU, its standard!

I’m guessing the manifold has messed something up slightly, but no idea what??? Any suggestions? I’ve checked for anything obvious, all the pipes around the inlet & maf all look OK and the whole system was fitted by local (and much trusted) mechanic so I’m confident it’s all been done correctly. I also extended both lambdas but ran the car for several weeks with them extended before fitting the milltek and everything was fine. I’m happy with the extra oomph the system has released but not happy with this slightly rough running when just driving at normal speed / cruising.

 

[RoadWarrior]

I would have gone down the TAPE ECU with a Racing Puma map. It's much better. Also, the TAPE only requires one lambda sensor.

I put money on your lack of one or two lambda sensors in your 4-2-1 is creating these problems, as the car doesn't know how much fuel to throw out. So it's running rich/lean all the time.

Also, I'm assuming you now have a EML on? You can plug lamda #1 in to the 4-2-1 if you modify the cables to be way longer than they were. And then get a plugin thing to trick the ECU into thinking the second lambda is present. But I haven't seen any of them in a long while.

 

[paulous]

I had the ECU remapped over a year ago before I realised the TAPE ECU's weer more tunable. Can I actually fit a TAPE ECU to my car?? Is it a simple swap, if it is then yes I'd be tempted to buy a FRP mapped TAPE and just swap if for my DIVE ECU. IS it that simple tho ??

My car has two lambdas as standard (it's a 2001 model). One before the cat and one after. For the before cat lambda I extended the cable myself using another cable I got from my local breakers. For the post-cat lambda I bought an extension cable from Pumaspeed - the pre and post cat lambdas have differing connectors and I couldn't find an extension cable anywhere to match the green pre cat one, hence I DIY'd it. I ran the car for a few weeks with the wires extended on the old exhaust system and didn't have any problems, no EML, so I think the cables are working fine. They just needed to be longer in order to reach the holes in the new milltek exhuast system as the cat effectively moves further down the system. So in theory all I've done is extend the cable to allow them to reach the actual sensors on the milltek system - I still have one pre-cat and one post-cat sensor and my engine mgt light isns't on so I think they're working. Just the slight hesitance I've described :-(

 

[tuonokid]

Check for air leaks in the exhaust system by putting a rag over the end of the exhaust. If there's an air leak between the head to just after the second lambda your lambda sensors can misread.

 

[Waterboard]

Book her into a decent speed shop and get it on a rolling road. Every engine is different and yours probably needs setting up.
Have you had any port work in the cylinder head or is it still stock??

 

[paulous]

Thanks for the advice so far... Just after fitting the exhaust there was a very slight raspy noise so I went back and they did exactly that... Rag over the tailpipe and checked for leaks, there was a very slight leak at the sleeve joint AFTER the cat (and second lambda) so they adjusted it, and tightened it up and the leak was gone. I might get it checked again but I don't think it's air leaks now.

Can the lambda sensors get damaged when moving?? Maybe I need a new pre cat one, isn't that the only one that actually adjusts anything?

I haven't had any head work or anything else modified, yet! Thinking of LMS or FRP inlet if I can ever find one. Maybe I do need to get it in a rolling road. I'll have to look up my nearest (I'm in Hertfordshire if anyone has recommendations).

 

[RoadWarrior]

The DIVE to TAPE is fairly simple. Unbolt & remove the DIVE, then relocate pin #80 to pin #75 on your wiring loom and off you go.

 

[RoadWarrior]

If it isn't throwing a eml, have you got a reader that does livedata? Check the fuel trims if so. Just take it for a spin and see how it's fueling. Another option is to check the spark plugs, only remove and install spark plugs on a cold engine.

There's no point in changing ECU now. It'll just be a waste of money.

 

[lusid666]

Just a thought, are you using your air con? The compressor kicks in about every 10 seconds and will pull a little power from the engine and can give the same sort of symptoms you are describing.

 

[RoadWarrior]

Aircon will make the car idle to about 1200rpms, then drop to 1000rpms.

 

[paulous]

I'll double check on the aircon (will try with it on and off), but I have been driving the car quite happily with aircon for over a year and it's only since fitting the 421 that the problem has appeared.

I don't have a reader but my local garage probably does, I could ask them to check for error codes.

 

[lusid666]

Failing that, have you tried this?

https://www.projectpuma.com/viewtopic.php?f=13&t=30000&p=353877&hilit=ecu+reset#p353877

 

[RoadWarrior]

If there's a problem on the DIVE ECU they keep the engine light on. Only the TAPE ECU has the inability to keep the light on, but the codes are stored if there is a problem.

 

[paulous]

My car was running absolutely fine before I fitted the 4-2-1 system, which included swapping the standard cat (as it's part of the old manifold) for a sportcat slightly further down the system. It's still running 95% OK, just the strange behaviour when cruising.

So surely the issue is related to the exhaust system or airflow??

I wasn't aware of the ECU reset procedure, I could try that. Daft question tho... the remap doesn't get erased does it!?? Pumaspeed told me it was permanent, even if the battery is disconnected for a lengthy period.... just checking tho!?

 

[lusid666]

No, it wont erase the remap.

 

[DOH]

In addition to the above advice, check that both the lambdas are tight in case 1 has worked loose and its sucking in air there.
Also check your wiring loom extension lead is still ok that was made for the new position of the lambda sensor.
Yes, the lambdas caneasily be damaged when removing if an impact gun is used to undo ( or a hammer ) as these are very delicate as they have an internal heater element in them that ensures the lambda is at the correct temperature to operate correctly.
If that is faulty, it will show up on an OBD reader