Engine Issues with a QLD Circuit Racing Excel

[benno]

Hi guys,
long time lurker first time poster.

We have an intermittent problem that is causing significant power loss - in the last race I was placed 4th when it hit, and was subsequently overtaken by nearly every single Excel within two laps - even the guys that are 8-10 seconds a lap slower than me.

The symptoms are this:

it occurs only intermittently, possibly worse when hot
significant power loss above a certain rpm
engine won't rev easily when it occurs
loud high pitched metallic clanging noise
I don't think the noise is detonation per se, but pinging seems like an accurate way to describe it.
It goes away if I let off the gas and let the revs fall - power below that certain rpm range seems unaffected.
I can't reproduce the noise revving the engine in neutral - it seems to happen only under load


I've no idea what the hell is going on. It seems related to both load and RPM. Something in the top end maybe? Would a dodgy injector or other fuel system problems cause it? Are there any likely culprits in the fuel system?

It may be easier just to find another engine and stick it in, but we've already done the timing belt/water pump in this thing and it was pretty strong up until now. We might get a dud with another second hand engine. On that note, if anyone in brissy has an engine crane they could lend us that would be so awesome.

So, collected engine gurus, WTF is going on?

Actually, anyone have a compression gauge or better yet, facilities to do a leakdown test? Or an OBDII reader?

[Mooa42]

Could be a fuel pump or fuel filter issue, needs more fuel under load and up in the revs??

Can't imagine that it's a mechanical issue, sounds fuel or electrical related.

I'd start by draining the fuel filter, undo the bottom and let it drain then see if that makes a difference. Fuel pumps can split in the top hose inside the tank which can lessen the pressure build up in the line, which isn't normally an issue until the engine starts to need all the fuel.

[Dave Scott]

Could it be in the exhaust (maybe the catalytic converter causing a blockage).

[Grumblebum]

Had a similar problem last year No power-then power-no acceleration but if you lift off it would pick up--answer exactly what Tony said broken fuel fitting in tank allowing air into fuel flow.:(
Let the group know what eventually turns up.
Regards Grumbo

[benno]

Thanks for the suggestions guys. A few people have mentioned the cat thing so I'll definitely check that one out.

Grumble can you tell me more about this fuel fitting? Did you have to drain the tank?

Just need some time in the mandate now...

[Grumblebum]

Yo lift up back seat and under a metal plate [held down by 4 screws]-you'll find a jumble of pipes and wires. Carefully remove the wiring then you'll see that a plastic ring holds the fuel pump into the tank. You can remove carefully the fuel hoses then gently tap the plastic ring anticlockwise. Once the ring is removed you can gently remove pump assembly-also includes fuel gauge sender-and it does require a little bit of jigiling.
Once you have exposed the pump very carefully examine the plastic outlet at the top of the pump-these get brittle and brake over time-which was the problem I had. As pumps are relatively inexpensive I would recommend you change it as you've already done most of the job.
Please take it easily and gently as the pumps are "sensitive" and the fuel lines may also be a bit stubborn.
Regards Grumbo

[Grumblebum]

Oops providing its not full you dont have to drain the tank but please don't smoke:spank: G

[rally_toy]

what do the plugs look like? will soon tell you if its a fuel problem

[benno]

I finally got some time to play in the garage, thanks everyone for your input. I think I've identified the problem:
http://i50.photobucket.com/albums/f305/benno_hew/3c871f5e.jpg

And the prize for the correct diagnosis goes to..... Dave Scott!!

That was a little ball shaped piece of dying catalytic converter that I think was rattling around in there and obstructing exhaust outflow every now and then.

I hope that's what it was anyway, eitherwise I'll get nailed again next time I go to the track.

rally-toy - the plugs were a nice tan colour, but I don't think that really means much given it was working well below a certain RPM range and I drove it all the way home after the last race.

[rally_toy]

the plugs would have helped you decide if it was a fuel problem thats all... wasnt suggesting the plugs were the problem

certainly looks like the cat was the problem