I'm really scratching my head over this one, - I'm hoping that someone might have an idea about this!

I've got a Mk3 Escort 1.6i that I've converted to EFi. I've changed the entire loom to one from a Mk4 Efi one, and I've replaced the old MFi head and inlet manifold with the EFi one. To get around the CPS problem I've used a 36-1 trigger wheel mounted onto the original front pulley, and a pickup off an 1800cc Sierra. It has a 1AFA ECU fitted with a superchip.

The car starts perfectly, and seems to run OK. But it is down on power and doesn't seem to want to rev up past about 5000RPM. I thought this might be my imagination at first but I had the car put on a rolling road,
and peak power was 96.9BHP @ 4920 RPM and 105.8 lbft @ 4050 RPM. After 5000 RPM the power dropped off rapidly but the car doesn't misfire - it just seems to hold back. When it was on the rollers the lambda reading was around 0.75 which is apparently quite rich. But when the operator checked the mixture at idle the CO reading was about 0.3% which is lean. He also noticed that someone has been playing with the fuel pressure regulator as the cap was missing.

When the car is cold it seems worse. It will start fine and run OK, but if you try and pull away quickly it seems to hold back at about 3000RPM, but this clears up once the car is warm.

I have swapped the EDIS, MAP Sensor, TPS, Fuel Pressure Regulator and mixture adjustment pot, none of which makes any difference. I have removed the superchip and it is exactly the same. I've tested the resistance of the CTS and the ATS and they seem reasonable. The CTS reads about 22k when the engine is cold, and drops to about 4k when it is
hot. I have tried running with the CTS and ATS disconnected and the problem is still there but it seemed to hold back at about 4000RPM rather than 5000.

I've used a fault code reader to put the engine in diagnostic mode, and checked the timing with a lamp. It is exactly 10 degrees with the octane adjustment lead disconnected, which I think is correct. I've checked the cam timing and both timing marks line up correctly. The car does not log any error codes in the ECU either.

If it was always holding back at 5000RPM I would think perhaps the camshaft is worn, but I think it unlikely as the engine is fairly quiet - there is a slight tapping at idle but nothing major.

I suspected the CTS, but the readings I've done seem to indicate it is working, and it is worse when it is disconnected altogether. Do these get inaccurate when they get old or just stop working altogether? I imagine they probably just stop working.

The only other thing I can think of is the CPS, - but I think it runs too well for that. It doesn't misfire or hesitate it just doesn't want to rev up...

Has anyone got any ideas because this has got me completely stumped.
Thanks for any suggestions you can offer!
Mark

 

0.75 is way too rich for a N/A motor and will make for sure the engine feel sluggish.

 

Thanks mate. What could be causing it? Could it be the CTS?

I've been told that the mixture adjustment potentiometer only adjusts the mixture at idle so there is no point adjusting it. Does that sound right or does it affect the mixture across the rev range?
Cheers
Mark

 

You mention about cam wear..........valve springs......

Just a thought. Theres allegedly a lot of aftermarket springs which are weaker than standard items, and CVH's suffer with valve bounce anyway because of the high rocker ratios and the excessive spring loads needed to control them at high RPM.

Just a thought

 

Thats a good idea.

I think this has got to be cam related. I've adjusted the mixture and nothing makes any difference it just loses power at 5000rpm.

Is it possible for the cam to have enough wear to cause a drop in power without the top end getting really rattly? It rattles a bit but nothing like some I've heard...

 

As a rule, if the cam is worn badly, they will tap, because of the wear and the fact the followers can't take up the clearance in the valve train.

Some people say they have seen worn cams that don't tap.........i myself i can't see it though.

Has the car had a performance shaft at any time?

If you look on http://www.pumaracing.co.uk/cvh.htm its got quite a lot of info on the top end

 

Thanks for the link - a lot of good information there.

I agree with you about the fact the if it doesn't rattle badly it can't be too worn. But this problem has got me thinking that presumably the lifters are capable of taking up a certain amount of wear before they start tapping. As mine is tapping slightly I thought that perhaps they were at their limit...

I don't actually know what cam is in the head. I bought the head second hand from a breakers. It is extremely clean inside which is why I chose it but it doesn't look like the cam has been out in some time. I can't see if it has a part number on the end as it has the blanking "core plug" in the way. Would it be worth taking the cam out for inspection?

 

You can tell a lot by removing the lifters as to what state the lifters are in, but read that webpage before u do, focussing on the bit about if the lifters dont want to pull out.

If they do that, the cam is fucked, end of story! IF they do pull out cleanly, any dishing on the bottom is the next sign of a worn cam!

A good cam will be silent (believe it or not)

There are ways to modify a CVH head and certain parts u can use to completely eliminate wear, but im still experimenting and ive been giving it a lot of thought and brain ache so im not going to say too much

 

Aah, when I was inspecting the head after buying it two or three of the lifters had burring at the bottom which made them difficult to get out. Consequentially I left them in place.

Sounds like I need a new cam then!

Is it worth getting an uprated shaft on a more or less standard engine or do you think I should go for a standard one?

 

I think increasingly more people are going back to running standard cams, but personally i wouldnt know what to advise.

A cam is nothing without a chip etc though

 

I've got a superchip fitted, but its only a normally aspirated CVH not a turbo one.

I was thinking of a CVH32 but don't know really.

 

Well I've taken the cam out and it seems very badly worn, especially on cylinders 3 and 4.

I'll stick a new cam in on Saturday and see what difference it makes!

Thanks for all your help.
Cheers
Mark

 

Number 4 is the favourite for wear, although when my cam went it was the exhaust lobe on number 3!

Again the Puma website will explain it all and save me typing it

Get some pictures up of the lobes, be interesting to see how bad it is

 

Just finished replacing the cam - I can't believe the difference it's made. It is hugely faster. The revving problems have gone and it pulls better down low as well.

When I compared it to the new cam it appeared that some of the lobes were as much as 3mm down on what they should be. Despite this the car did not tap/rattle. It's amazing that a cam can be so badly worn and yet not make any noise!

I'll get some pictures of the old cam up tomorrow.

Cheers
Mark

 

3mm

Glad you sorted it Would like to see pics of that!