×

Sale ends todayGet 30% off any course (excluding packages)

Ends in --- --- ---

Terrible Idle quality, not pulling vacuum with mild cams

General Tuning Discussion

Forum Posts

Courses

Blog

Tech Articles

Discuss all things tuning in this section. News, products, problems and results. 

= Resolved threads

Author
718 Views

I've got a new motor build, Ford Duratec 2.4l. It's got 12.7:1 compression, and 8000rpm redline.

I'm extremely happy with the power and torque it's making. The car pulls HARD from 2000rpm all the way up to the redline. It's completely transformed this car, it is fast!

The problem is the idle is horrendous and I can't figure out why, and nothing seems to help.

The camshaft specs:

Intake: 242@050, 11.3mm lift

Exhaust: 222@050, 9.95mm lift

These are relatively mild cams. I expect some lope, but not to this extent.

A professional shop that builds these motors with this same cam on a daily basis sets their idle at 900 and it's smooth for them apparently. I'm not expecting that low, but it would certainly be nice.

Right now I'm only trying to hit 1200rpm, and it's not working out. It requires a HUGE throttle opening and spark advance, just to prevent stalling. It needs about 8-9% throttle and 20+ degrees advance to hold 1200rpm, for comparison the same stock motor held that rpm with 3% throttle and 15degrees advance.

It's barely pulling any vacuum at all below 2000rpm, the best it's hitting is around 80kpa. If I rev it over 2000, it pulls vacuum down to a very solid 40kpa.

I tuned a friends motor with similar cams, his idled at 1200@60kpa at around 4.5% throttle. I'd settle for that right now.

I've tried tuning everything, playing with different throttle openings and spark advance, changing target AFR and injection timing, nothing made any difference at all.

It's an Emtron KV8 ecu, and a DBW throttle. So I have alot of things I can tune and adjust, but nothing has helped so far.

I'm thinking there must be some problem, or something substantial that I am missing here.

I've searched for vacuum leaks, haven't found any. I don't think that would cause the symptoms I am seeing anyway.

What are my options? What should I be looking for or at?

Ffirst thing I'd be looking at would be if the TDC was correctly marked, IIRC, these engines (if it's what I think it is?) didn't use a keyway, so it's possible it isn't where it should be?

Once I'd confirmed the actual TDC, I'd check the camshafts were correctly timed as that can make a big difference and, while doing so, I'd double check they weren't accidentally fitted the wrong way round - I don't know about that specific engine, but with some it's possible, if unlikely.

If the TDC wasn't correctly established, it would also throw off the ignition timing and you may not have what you think you have.

I assume you've checked the DBW is correctly calibrated and you're getting what you think you are there?

You don't mention the intake and exhaust side, they can also make a huge difference, especially as using some types of MAF are VERY sensitive to reversal at low rpm.

Yeah, it is the engine you're thinking of.

Normally the crank is un-keyed. But this one has a keyway added. So, the crank gear and timing pulley are locked in position. The only timing adjustments available are the cam gears, and the crank sensor position.

I just went and checked the basics. The crank sensor is bang on perfect, so I know the ignition timing is accurate.

The intake cam is also perfect. However the exhaust cam is slightly retarded. The timing bar wouldn't quite slide into it. I'd say 1 or 2 cam degrees retarded, so maybe as much as 5 crank degrees. So there is more cam overlap than there is supposed to be... I'll correct that tonight and see how much difference that makes.

It's not using a MAF sensor, just running MAP right now. Once I get it setup work working nicely I'll tune the TMF, and that's how I plan to run it.

The intake and exhaust manifolds are both made by Cosworth. Throttle is 68mm DBW, slightly large for the application but not excessive.

The throttle position was correctly calibrated. But I haven't double checked in a while, so it's worth a check.""

Keyed crank: