7M detonation with near-stock engine/ecu

**Bored?** · 30-06-2007, 06:23 PM

Background: my 7m-gte has just been rebuilt, and along the way some mild mods were done: Head porting, 2mm cometic MHG, Block and head machined flat
Wiseco forged pistons, 1mm over-bore (with corresponding bore/hone). The car is running on 98 octane BP or shell fuel.

Engine wise everything else has been left stock, though the car also has been converted to manual and had ABS disabled.

The problem I'm seeing at the moment is that the car runs pretty well up top and on boost, but between 1000 and 1500rpm I hear pinging under all but the slightest throttle openings.

So far in troubleshooting, I've:
Retarded the cam angle sensor as far as possible, this slightly improves the amount of pinging, but didn't eliminate the problem. Also this seemed to reduce power in top end noticeably.

Searched the intake system for leaks - I found and fixed one hose that was left off in the build, but other than that wasn't able to find any leaks. Fixing the hose that was off didn't seem to have any effect.

Tried running with O2 sensor disconnected - didn't seem to make any difference. I figured this would make it run at maximum rich compensation. Could be wrong.

I'm almost at the point of buying an SAFC to put more fuel in at low revs, but I thought I'd ask for any other ideas first. Keep in mind that the whole engine has just been rebuilt, so there are lots of potential things that could have been set up wrong.

Ideas?

**abently** · 30-06-2007, 10:41 PM

Best guess you'll get is that you've raised the Static CR a little, with the Factory Timing and Fuel Maps too aggressive at that point.......

**whatthe?** · 30-06-2007, 10:46 PM

Raised comp with a 2mm HG? I would've thought the opposite unless the forgies are high comp items or they took a shitload out when they skimmed the head and block.
Injectors all good?
Timing belt or CAS not a tooth out?
Fuel pressure reg OK?
Fuel pump resistor ok for 2 speed pump (assuming MA70 or MZ20 here)?

I'd get it on a dyno or chuck a wideband on it and see what fuel is doing at the aforementioned revs if I were you

**amichie** · 30-06-2007, 10:54 PM

Also check your knock sensors are tight in the block. i think the 7mgte has 2 under the inlet manifold.

Should be torqued upto 36 foot pounds.

**abently** · 01-07-2007, 03:31 PM

Do you know the Volume (CC) of the Forged Piston ? Or at least what brand they are ?

Because other then that, it would have to be a Fuel issue, so as whatthe? said, Injectors, Fuel Pump and Fuel Regulator (Possible vaccum hose issue rather then regulator....).

A dyno would be the best thing to use to pick out the problem, unless you have an Electronic Fuel Pressure gauge (Mechanical ones are only legal if they are not located in the cabin) ?

**Bored?** · 02-07-2007, 11:34 PM

Grr. Toymods is breaking on me. I just typed a whole message and lost it.

Thanks for your ideas guys. The pistons are wiseco 7m-gte. I would have thought a 2mm gasket would more than compensate for the machining, but maybe not. I'm not planning to pull the motor down to find out anyway.

Cam timing and CAS timing we're pretty confident about. Pulls to redline ok, and timing light shows ~10 degrees at idle, excepting that I've now screwed around with it a bit.

I guess it could be fuel pressure, but wouldn't it be a bit strange to not have enough fuel pressure at such low revs? I'll have a look into the fuel system in a little bit more detail anyway.

I'll take a peek at the knock sensors too - they may have been missed when wiring the engine even - they're hard to see once the manifold is on.

**whatthe?** · 02-07-2007, 11:37 PM

Dont forget the fuel pump/resistor. It's a two speed job, maybe it's not switching to high speed early enough?

**abently** · 03-07-2007, 01:35 PM

Stock 7M-GTE CR is 8.4:1

Wiseco Forged Pistons (83.5mm) CR is 8.95

Extra thickness from Head Gasket will drop the CR to 8.32:1

How much was shaved off the Head and Block will bump up the static CR back up again......... impossible to know unless you asked the Machine shop at the time it was done...

Just buy a SAFC and add some Fuel in once you have triple checked everything else.

**o_man_ra23** · 03-07-2007, 01:51 PM

I would stick it on a dyno and find the problem before trying expensive solutions (SAFC for example) It could simply just want a different/new fuel regulator... or it may need a massif re-tune. Dont forget that forged pistons are known to be noisy (especially when cold), perhaps the knock sensor is picking this up as knock noise??

Cheers, Owen

**abently** · 03-07-2007, 02:33 PM

Originally Posted by o_man_ra23

I would stick it on a dyno and find the problem before trying expensive solutions (SAFC for example) It could simply just want a different/new fuel regulator... or it may need a massif re-tune. Dont forget that forged pistons are known to be noisy (especially when cold), perhaps the knock sensor is picking this up as knock noise??

Cheers, Owen

He has stated 'he hears pinging', not that the Knock Sensor is picking it up, in which case it would then retard the Timing, not advance it to 'Knock' even more......