3.9 EFI Megasquirt idle and low speed running problems

kiwicar · Post by **kiwicar** » Tue Jun 29, 2010 7:13 pm

90 degree elbows will restrict flow allot and will make the flow very turbulent, this could make the pump cavitate.
Best regards
Mike

stevieturbo · Post by **stevieturbo** » Tue Jun 29, 2010 7:18 pm

True, although it does still sound like an adequate supply.

BenL · Post by **BenL** » Tue Jun 29, 2010 7:31 pm

@kiwicar: That's what I read last night on some googled info about Fuel Pump cavitation. It's worth a try so I'll try the afformentioned copper tube with formed bends to see.

I have to say the car didn't idle well on the weber 500 and distributor(tried every dizzy setup in the book) before. I presumed it was the weber 500 at fault as I had trouble with poor idle from one before. This makes the EFI conversion all the more disappointing. I have wondered if there is something fundamental wrong with the engine but:

It's a 40,000 mile RPI unit that was well looked after.
I've done a compression check and it's all come up well.
I've checked the cam is timed correctly using a dial gauge and timing disc.
It does't overheat or use any coolant.
It give a reasonably good idle vacuum of 15-16hg

zim · Post by **zim** » Wed Jun 30, 2010 12:28 pm

Sorry i can't help on the idle - my 4.2 can idle at about 800ish with the idle control valve blocked off.

On another topic, i see you've mounted your inlet air temp sender in your plenum - how are you finding this ? is it ok ? i was a bit scared of doing that due to the plenum getting warm.

Gordon

BenL · Post by **BenL** » Wed Jun 30, 2010 12:48 pm

The air temp sensor in the plenum giving a false reading wasn't something I thought about at the time. I think it usually reads up to about 70deg but it isn't something I have really checked at this stage.

Wouldn't be too much trouble to move it though. Where did you site yours?

By the way what is idle quality like at 800rpm?

DaveEFI · Post by **DaveEFI** » Wed Jun 30, 2010 1:58 pm

BenL wrote:The air temp sensor in the plenum giving a false reading wasn't something I thought about at the time. I think it usually reads up to about 70deg but it isn't something I have really checked at this stage.

Wouldn't be too much trouble to move it though. Where did you site yours?

By the way what is idle quality like at 800rpm?

I replaced the flapper AFM with a length of tube, and mounted the air temp sensor in that.

BTW, you never get a perfect idle on a V-8 - not like a straight six, anyway.

ChrisJC · Post by **ChrisJC** » Wed Jun 30, 2010 2:47 pm

DaveEFI wrote: BTW, you never get a perfect idle on a V-8 - not like a straight six, anyway.

What makes you say that?

Chris.

kiwicar · Post by **kiwicar** » Wed Jun 30, 2010 2:51 pm

"BTW, you never get a perfect idle on a V-8 - not like a straight six, anyway".
Don't tell rolls royce that they will be most upset!

Best regards
Mike

stevieturbo · Post by **stevieturbo** » Wed Jun 30, 2010 5:30 pm

Or Lexus...

TVRleigh · Post by **TVRleigh** » Wed Jun 30, 2010 9:38 pm

Sorry to take it slightly off topic,
But why do you want a 600 RPM idle. I'm happy if mine idle ok at 1k
Also mine idle AFR is set at 13.8 on the Racer with emerald.

Also I noticed you are running a Pipper 270 camshaft, are you sure that should idle that low.

Also regarding the fuel pumps I'm running a Redtop pump to a swirl pot (with inbuilt filter then to the main pump on the racer, but the TVR just runs just a swirl pot to a Sytec Filter then main pump.

BenL · Post by **BenL** » Wed Jun 30, 2010 9:39 pm

Well found one problem today. I'd fitted a piece of pipe onto the end of the tank fuel return to direct the flow away from the pickup. Pulled it out today to find it had been to close to the bottom of the tank and so had a kink in it... maybe explains why the pump sounded a bit strained at times!

Re-made it with a piece of solid tube and....... no difference to the idle but the pump sounds better. Still makes the cracking noise (I suspect turbulent flow rather than anything catastrophic) once in a while but I'm not sure it's that significant.

Checked the temp of the fuel filter by hand after a 45min run and it was just slightly warm to the touch. That's with 1/4 tank so I don't suspect the fuel is getting that hot.

HOWEVER!

DaveEFI's comment about the IAT sensor got me thinking. I have noticed that the idle is paticularly poor if sitting in traffic or after a hot restart. This suggests that maybe the heat soak from the plenum is giving a false reading. It could also explain why I have noticed that the idle when pulling up at lights after driving at a reasonable speed for a while will mean the idle is improved. The constant flow of air has possibly resulted in a correct reading for the IAT.

Will be making up a new adaptor to place it between the inlet hose and the air filter. Will also have a look thro some datalogs and see if there is any evidence there.

BenL · Post by **BenL** » Wed Jun 30, 2010 10:04 pm

@TVRleigh:

I don't think the 270/110 is that wild a cam looking at the timing and lift figures but I could be wrong. As for the solid and low idle I just love that effortless sound and feel.

After driving it a bit over the last couple of days and the recent discussions I have renewed my enthusiasm for getting it sorted. It runs beautifully under load and perhaps rather than worrying too much about the idle I think I will concentrate on sorting out some of surging at low speeds and the afformentioned IAT problem.

Was daydreaming about a 4.6 tho!

TVRleigh · Post by **TVRleigh** » Wed Jun 30, 2010 10:09 pm

BenL wrote:@TVRleigh: I don't think the 270/110 is that wild a cam looking at the timing and lift figures but I could be wrong. As for the solid and low idle I just love that effortless sound and feel.

True but I would have thought 600 RPM is very low for anything other than a very mild camshaft.

The 190 BHP is that ATW or fly.

BenL · Post by **BenL** » Wed Jun 30, 2010 10:23 pm

This is the ATW dyno plot. The 190-200 is a guess at the flywheel power since we didn't do anything to evaluate transmission losses.

The car is running standard cast exhaust manifolds and unported late heads. What does that suggest to you in terms of cam spec? It doesn't feel that cammy but it certainly pulls well right up to the red-line.

DaveEFI · Post by **DaveEFI** » Wed Jun 30, 2010 10:42 pm

kiwicar wrote:"BTW, you never get a perfect idle on a V-8 - not like a straight six, anyway".
Don't tell rolls royce that they will be most upset!
Best regards
Mike

They'd be the first to admit it. Or rather did, when they introduced their V-8 and discontinued their 6 in the early '60s. With the six, you could stand an old fashioned three penny bit vertically on it with the engine running.