Flat spot above 4.5k rpm after cambelt change

[tomislav]

Hi people, have an issue but will give you the background to it as well, maybe it will help the diagnosis.

Changed the cambelt on my M20B25, when i timed it all up on the marks it turned out the camshaft was a tooth out, advanced. The car has never been quite as 'on the money' as my last 2.5 and also idled like shite from cold so i thought 'huzzah, i've found my missing horsepower!'.

Fast forward a couple of days and the car has also had another air flow meter fitted that has never had the top off, electric fan and thermostat, yaddah yaddah yaddah.

Got it back on all 4 wheels last night and went out on a 'private road' to test it.

Flat out, 118mph in 4th with a huge flat spot from 4.5k to 6.5k rpm.

It just feels flat through the revs but as the car gets 'on cam' it goes then backs off, then goes, then off all the way to the red line.

I'm gonna try and get a timing light tonight to check things over but has anyone ever known the woodruff keys in the cams to wear allowing the pulley to move ar anything?? And does anyone know what the degrees of advance/retard should be on idle, at 3000rpm or whatever?

Please help, going to the 'ring in 2 weeks!!!!!!!!! Worse, i only have til the 25th july to sort this.

Thanks in advance

Tom

[capnmchl]

I would imagine if someone has done the cambelt with a tooth out, then there is a possibility someone has adjusted the ignition timing since and done it to that.

Now that you've rolled the camshaft forward a tooth, the ignition timing is forward '1 tooth' and therefore won't be running right.

Basically, I'd redo the ignition timing before starting anything else.

I'm afraid I can't tell you the timing though, Autodata won't let me log on.

[gromgsxr]

Thought the ignition timing was set by the ecu and not adjustable.

[maggspower]

The cam has a pin rather than a woodruff and if it is there is very reliable.

I would imagine if someone has done the cambelt with a tooth out, then there is a possibility someone has adjusted the ignition timing since and done it to that.

Now that you've rolled the camshaft forward a tooth, the ignition timing is forward '1 tooth' and therefore won't be running right.

Basically, I'd redo the ignition timing before starting anything else.

I'm afraid I can't tell you the timing though, Autodata won't let me log on.

What??? Ignition timing cannot be "set" it is inbuilt within the motronic unit, taking readings off the crank sensor, throttle switch and air flow meter.

The problem with changing loads of parts then finding a problem is narrowing it all down.

Check your cam timing again, just to make sure. If this is right then start looking at the fuel, intake and ignition. Start with a physical check of crank sensor, ignition leads, distributor cap and rotor arm. Next get the multimeter out and start doing some checks on the TPS, AFM, coil, etc

[tomislav]

Right, car is fixed, bit wierd how tho.

So, checked the timing when i got home from work yesterday, all spot on. Stripped off the dizzy cap, rotor arm, pulled of the camshaft sproket, all ok there too.

Now my car has some shitty aftermarket fuel pressure regulator fitted to it and my conclusion goes like this.

Before i had the car someone told the owner at the time 'hey, did you know if you advance your cam timing and bung in more fuel your car will be faster'. So the owner has had the timing moved a tooth and this gash regulator has been used to adjust the fuelling.

I returned the timing to where it should be and then its running flat.

I wound the fuelling up on the regulator to just under 3 bar (indicated by the gauge on the regulator, it was 2 bar before) and hey fu*kin presto, car now goes like a bloody rocket ship!

Never underestimate the power of stupidity, a little bit of knowledge can be a bad thing!

[maggspower]

Good news

Get rid of that adjustable fuel pressure regulator and get a proper one. Some one may even buy your current one on a popular auction site

[tomislav]

Bought one off the zone a few days ago, just waiting for it to arrive

[kam-325i]

I wound the fuelling up on the regulator to just under 3 bar (indicated by the gauge on the regulator, it was 2 bar before) and hey fu*kin presto, car now goes like a bloody rocket ship!

3Bar is what the fuel system should be running at. the engine would of been running out of fuel at the top end @ 2Bar....

[capnmchl]

Sorry about the disinformation, used to M10 stuff, which you wouldn't even have to change a belt on

[Brianmoooore]

Before i had the car someone told the owner at the time 'hey, did you know if you advance your cam timing and bung in more fuel your car will be faster'.

You broke my number 1 rule of car buying, which I've posted on here several times!
"NEVER buy a car off of an idiot!"

[tomislav]

Sorry brian but the guy i bought it off i dont think was an idiot, it was the one before that. Its just one of those cars where everything you look at and check has been lashed up, so i'm now in the process of putting all right and will then end up with a half decent car.

The difference in performance is now staggering.

I'm assuming i should aim for 3 bar on the nose? Its at about 3.2 bar at the moment

[Brianmoooore]

It's 3 bar relative to the pressure in the inlet plenum, not measured relative to atmosphere.
Best plan is to get rid of the aftermarket regulator and fit an OE one, before it does the "leaking fuel into your engine compartment" trick they are known for.

[tomislav]

already did that! The nice braided hose from the tank went pourous, started it up a couple of weeks ago, popped the bonnet open, fuel going everywhere!!

[Speedtouch]

I had the cambelt changed on my first E30, a 1984 320i L-Jet, at a Halfords centre in Essex. I'm sure they fitted the belt one tooth out, because it had a flat spot similar to what you described afterwards.

[AardHawk]

They upset the position of the intermediate shaft, which then changed the ignition timing. A schoolboy mistake.

[tomislav]

The intermediate shaft doesn't do the timing on an m20, it drives the oil pump doesn't it? Earlt m20's yeah but not this one

[gromgsxr]

correct timing is all done by the ecu on a 325 and non adjustable, early engines had a propper dizzy driven off that intermidiate shaft sticking out the engine under the inlet manifold

[Speedtouch]

Welcome to the Zone, Aardhawk - and congratulations on your first post in eight years!

Yes, you're probably right about the intermediate shaft getting nudged. I suppose I should have tried adjusting the distributor, but I sold the car fairly shortly afterwards.

[tomislav]

correct timing is all done by the ecu on a 325 and non adjustable, early engines had a propper dizzy driven off that intermidiate shaft sticking out the engine under the inlet manifold

Thought as much.

Doesnt the other end of that shaft drive the oil pump?

[gromgsxr]

It does drive the oil pump only on later cars.there a Ali cap to blank where the dizz used to be driven from near the front of the block on the inlet side.

[tomislav]

Yeah mines the later type so not involved in timing.

[AardHawk]

Plug the tps back in.

[tomislav]

What? Its not unplugged, plus the problem is fixed now anyway, it was timing and then fuelling.

[AardHawk]

You broke my number 1 rule of car buying, which I've posted on here several times!
"NEVER buy a car off of an idiot!"

You need to change that rule, to NEVER help an idiot!

[tomislav]

If thats aimed at me i'd love to know why.