So I have this nagging issue that has been evident for the past few months. It all started when I replaced my airbox with a pod filter. The car seemed to have almost no power then the power came in one big wollop at 4000rpm consistently. I then put the standard airbox back on and the issue remained. I then bought a brand new maf sensor direct from mazda which cost a bomb and it made no difference. I checked every singe sensor tps, o2 etc.. with a multimeter and they were all fine also no codes on the ecu. I took the car to the mechanic and he replaced the fuel filter. This seemed to improve the problem greatly although now when I push full throttle in second gear or lets say full throttle up a very steep hill, the power kicks in at about 4000 rpm like vtec

I have also replaced the ht leads about 2 years ago and spark plugs last month yet no improvement. Injector cleaner did seem to help but the problem is still there. Any ideas?

Thankyou.

Sounds to me like you may have disturbed an air pipe / vacuum pipe.

There's a mass of them around the inlet manifold and if some come adrift (or get holes) then the effect can be like you describe.

If you get a can of carb cleaner and spray the air/vacuum pipes, any air leaks should suck in the cleaner fluid. You should notice the engine revs drop slightly which should help identify any leaks location. Worked on my van that had a duff seal on one of the carbs.

Ok thanks guys, ill have a go with the carb spray and ill let you know how I got on

So I just checked, I didnt find any vacuum leaks after a good visual and audible tests. I then sprayed some spray around the vacuum areas but the idle remained steady throughout

Have you reset the ecu?? Might not make much difference as it's a bit of a basic unit but might be worth trying. Disconnect battery and press brake pedal for 20-30 seconds should do it. Ecu should then relearn with current air box setup. Also, is the tps set right? On mine I connected gnd & ten on the diagnostic port with bit of wire, turned ignition on, loosened the tps bolts and turn it fractionally until the fan kicked in then backed it off a tiny amount so fan stopped. Tighten bolts and away. That's on the v6 though, not sure if 1.5/1.8 are same....

Also, is the intake pipe definitely ok? You may have to remove it and check the concertina section as this is well known to crack in amongst the ribs. Flexing it by hand off the car should show any cracks. Mines filled with silicon sealant to make sure, sikaflex stuff for caravans etc, not bathroom stuff!! But tank/elephant/duct tape can be a temporary repair

I have not yet reset the ecu after I put the standard box back on, regarding the inlet tube, I changed it about 1 and a bit years ago to a new one from mazda although I will go and double check the tube again. I also sprayed a lot of spray specifically onto the ribbed area of the tube but nothing seems to happen. Regarding the tps, I dont think I ever removed it..about 3 years ago I took apart the intake manifold and cleaned the egr and manifold due to another hesitation problem with was solved by jb welding the black vacuum box although I can't remember removing the tps.

This hesitation seems to be intermittent, sometimes it heists, other times it doesn't. If the engine is hot or cold it doesn't seem to make a difference. What I have noticed is that under heavy acceleration in mainly second gear or if i go up a steep hill in first, thats when the problem arises. Im suspecting that maybe its a fuelling issue, maybe the pump is not up to standard, maybe the injectors aren't coping with high demand anymore, I'm not sure.

My TPS needed tweaking ever so slightly, but it only really made the car a bit more responsive according to my seat of the pants based dyno

I know on the side of my air filter box are a couple of small vacuum tubes, not sure on the Z5 but I presume these are all back on in the right order? no idea what effect mixing them up would have...

The Z5 doesn't have the vris does it? wouldn't know if that being stuck open would cause an issue.

Looking up 'hesitation under acceleration' most seem to point to either an air-leak or a fuelling issue. You should be able to get the injectors checked/cleaned. As for the fuel pump, no idea I'm afraid. My only experience there is with old SU carbs and mechanical pumps. If it's an on/in tank job, maybe worth checking the earthing on it? condensation builds up on petrol tanks really easily so it may have corroded a bit causing a bit of an intermittent fault?? (the fuller the tank the less condensation, hence my bike is always stored with a full tank o' gas).

Random thought, my mum's old Mk4 Escort had a faulty EGR valve that only manifested under acceleration and up hill, caused the car to stutter and hesitate. Turns out there was a small ball bearing inside the valve that would roll back and stick once it had gone duff. No idea how our EGR valves work, but it may cause similar symptoms if its playing up. Just an idea.

Not sure if this is of any use, how to clean the Z5 EGR valve from the ClubProtege forum:

http://www.clubprotege.com/forum/showth ... -with-Pics

Unless you have a pipe with a crack or hole that only really opens up under higher vacuum, no idea how you track that on though!

Thankyou for all the help Dark_Jon, I really appreciate your time. Taking in all we have discussed, when I have some more time next week, I'll have a look at the tps as I need to use the car at the moment. I'll also look more for some more possible vacuum leaks. I'll also chuck in some injector cleaner in the tank and see how that goes..if it doesn't clear it up ill have to get them professionally cleaned and see how that turns out

*Solved* - Wanted to re-visit this post..

The fuel system had pressure but not enough flow, the suspect, a 20 year old fuel filter and clogged injectors. The fix, a new filter and 4 tanks of petrol each with a dose of injector cleaner as stated by the manufacture. Total cost.. about 20 euros and 4 months of hell (excluding petrol cost)

Post number 1:


I think you need to have a "chat" with that mechanic..

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Speed is subjective to only how far you keep your right foot down..

Nice to see that the injector cleaner does actually work! I know their have been debates for many years now as to whether it actually does anthing.......glad you managed to get it fixed

I've seen a few different videos on youtube about fuel additives - more power increase orientated - and they make no difference what so ever, proven on a dyno

Fifth gear did a comparison on restoring power on an old Scirocco by comparing using a fuel additive to changing the air & oil filters, the oil itself etc.

https://www.youtube.com/watch?v=WQN-0zvZNbY

They said that the Redex was the most cost effective solution and the got about 6 bhp back. They were focused on restoring bhp not finding magical fairy dust solutions to increasing it over stock!

@Dark_Jon

In fact that is where I got the idea from... The first tank I used Lucas cleaner then in the last 3 I used reddex. There car seems to pull nicely from stop now all the way to redline.