Problems...please Help!

[CJspeedsport]

I mentioned on an earlier thread that I was having some rev issues. Has anyone ever encountered the following...

Firstly a bit about the car, which I purchased through a dealer over Christmas.

It is a 1.8 zetec with Jenvy TB's running and MBE 956 ECU. She was factory built in 2000 and seems to have been put together very nicely. 20,000 miles on the clock.The car will start first time and is generally very smooth.

HOWEVER, when I accelerate hard, (read foot to the floor) the engine hits the limiter at anywhere between 5000 and 5600 revs in 1st, 2nd and 3rd (I haven't hit the limiter in 4th). From what I can tell, it isn't always at the same point in the same gear. For example last night, I accelerated hard in 2nd from one roundabout and hit the limiter quite unpleasantly/abruptly at about 5000, from the next roundabout it got to 5500 and was the more usual end of revs experience. I was flooring it in both instances.

Interestingly, if I accelerate gradually, it will rev right through to 6800/7000 in all of these gears....?!

The engine seems to backfire a bit more than the other Westie's I have driven (which seemed to backfire a bit less as the engine warmed up, if anything it's the opposite on mine). Also when I try to blip the throttle on a down change, I hear a pop, not the same as a backfire (engine bay not exhaust) or nothing happens at all.

Last night I changed plugs and leads which has made no difference.

Does anyone have any thoughts or observations?

Really appreciate any help or advice.

Thanks.

[Jenko]

Whenyou say 'hits the limiter' what actually happens.

It's strange that it happens on full throttle but doesn't happen if you graduately accellerate. Could be the fuel map vs throttle position is not fully optimised, I also know that the lambda sensors can play up. But this is just speculation.......Do you have a rolling road nearby that can look at the car?.

[CJspeedsport]

Yeah, I'm going to take it to South Wales Tuning (www.sw-t.co), hopefully on Thursday.

It's hard to explain, not being as mechanically minded as I should be, but as you come up through the revs, you reach a point where the engine is no longer delivering power and it blips really rapidly. Last night this was happening at around 5500 with the exception of once where it happed at 5000 and this was quite a violent loss of power and one big "blip".

Listening to the whine of the engine increase as you hit the throttle, you're really not expecting it to do that when it does.

[Paul D Turner]

From what you say I would guess that your injectors are too small and that on full throttle you are hitting 100% duty which feels like a rev limiter coming in. Accelerate gradually and you use less fuel thus no where near 100% duty thus get to true rev limit.

[XTR2Turbo]

Also check feed to the fuel pump.

I had it on a car and was puzzled for weeks.

Turned out to be a poor connection on the fuel pump limiting fuel. Linked to this check fuel filter.

I think unlikely to be map now unless something fundamentally changed on the car.

[peterg]

clogged fuel filter, dodgy fuel pump?

[CJspeedsport]

Hopefully, South Wales tuning will be able to diagnose the problem a little more easily than me

[Rab (bombero) Reid]

Interesting and one, as you say, difficult to distant diagnose. At the risk of granny-eggs-suck, go through a methodical process over the engine. All advice so far are relevant and feasible. FWIW, my tuppence is:

• Check electrical connections - fuel pump, tps even ecu to be sure, battery, earths
  
• Check fuel filter(s)
  
• Check mechanical connections - TBs to manifold, manifold to head (response to your 'popping' from engine bay)
  
• Have SWT reset your tps before any ecu map checking/remapping
  

My suspicion is fuel delivery ..

[XTR2Turbo]

I would try to keep below the problem area until sorted properly. Quite dangerous to run an engine lean at high revs if that is the problem.

Try to avoid trial and error fault finding.

[John Loudon - Sponsorship Liaison]

I'm with Paul and XTR Turbo

[CJspeedsport]

Thanks for the responses guys. Some great advice.

I will report back when SWT have had a look. I'll have a look at the filter and pump before I go.

[Dave Eastwood (Gadgetman) - Club Chairman]

Another fault that can give the appearance of the rev limiter cutting in is a faulty crank position sensor, or excess noise on the crs wiring. Essentially, under normal circumstance it gives the ecu an accurate reading of the engines rpm, but when faulting it give a random, possibly zero reading. This instantly causes the ecu to adjust ignition advance and fueling to suit and can feel just like hitting the hard cut limiter. Observing the ecu outputs on the Easimap software when it happens will confirm immediately. (an analogue rev counter won't respond quickly enough to show the sudden change.)

[perksy]

Check TPS, Crank sensor and make sure its not running Lean up the rev range

They should be able to check this on the rollers

New set of plugs wouldn't hurt either, unless you've already changed them

[SteveD]

if you bought it from a dealer ,then it will have warranty ,contact them

[Martin Keene]

clogged fuel filter, dodgy fuel pump?

This would be my first place to look. The fact it has done 20k miles would suggest this is a new problem, which means thing slike injectors being too small are unlikely, and the fact it will rev out when revved slowly, but hits a variable limiter when revved hard, screams lack of fuel to me.