Flat-spot on Hunter/Granada 2-litre DOHC injection

[gouldsborough7]

Hi Guys
I think I raised an item along these lines perhaps a year ago, and to be honest I haven't taken any positive steps to cure the problem. I wondered if one of you may have some ideas? I am tempted to employ a local home-tune company, but that would probable mean shelling out £100+, which I don't want to do if I can find another cheaper way.

My engine goes very well, having only travelled 11,000mls+ since new in 1998. Acceleration from a standstill is very brisk, and the 'flat-spot' is hardly noticeable if aiming for 50mph or higher. If however I am in traffic and allow the revs to go below 2,000rpm down to 1,500rpm in any gear, the engine 'hunts' and the transmission jerks back and forward. It's not a major problem, but just spoils an otherwise good car. It always starts first turn of the key, and settles down to an even tick-over at around 1,000rpm.

The 2-litre DOHC fuel injection engine has no distributor (ECU under the dash), and has 2 solid-state coils serving the 4 platinum plugs.
The exhaust is standard factory stainless steel.

As far as I know, the engine has not been tuned up, but who knows with a factory-made vehicle? This would make some sense. I would be happier to know if it was the state-of-tune that required the revs to be kept above 2,000rpm, and not some malfunction.

When I first bought the car, I did try to extract any information at all from the factory, but it was like pulling Dinosaur teeth!!

Any ideas would be appreciated.
Cheers
Mike

[dogoncrazy]

Re: Flat-spot on Hunter/Granada 2-litre DOHC injection

Mike
My Cabrio [BMW powered] exibited problem not unlike yours. Would start ok idle reasonably well at 850/900rpm and would pull well with only a minor flat spot around 2000/2500 rpm, however would not like being held at those sort of revs. Tried all manner of things and even enlisted help from Peter Morris who substituted items from his Cabrio to no avail. Finaly found the cause when I decided that I would check the cambelt had been changed under its previous owner/builder life. It had but was A TOOTH OUT ! Took belt off and refitted in correct position. May be worth a look?

[csjcarolyn]

Re: Flat-spot on Hunter/Granada 2-litre DOHC injection

Hi Alan,
Should you refit a previously tensioned cam belt?

Roger

[dogoncrazy]

Re: Flat-spot on Hunter/Granada 2-litre DOHC injection

Hi Roger
Interesting question.As the engine had done less than 3000 miles since installation in the Cabrio and was presumably fitted with the new belt just prior to that I considered that removal/refitting shouldn't present an issue. Had it done say 1000 or moremiles i would almost certainly have binned it for a new one.

[dogoncrazy]

Re: Flat-spot on Hunter/Granada 2-litre DOHC injection

SHould have read 10000[ten thousand] not one thousand!

[gouldsborough7]

Re: Flat-spot on Hunter/Granada 2-litre DOHC injection

Hi Alan
I've heard somewhere on my travels in the past about someone's cambelt slipping a tooth. Your symptoms and mine are very similar. Trying to drive within the rev-band 1500-2000rpm can cause much backlash of the transmission, and even the feeling of engine conking out. When the latter happened the first time, I thought I was running out of petrol or something.

I double-checked in my recently aquired Haynes Manual - my DOHC engine is all chains! - camshaft and oil pump. Having had Cortina & Sierra engines in previous kits (with belts), I didn't realise that the double-camshaft engine was chain-driven.

So unless it was assembled wrongly, (factory built car, came with new engine in 1998) that area is ruled out. Would have been a nice easy cure though.

Cheers
Mike

[csjcarolyn]

Re: Flat-spot on Hunter/Granada 2-litre DOHC injection

Hi Alan,
I think it might be worthwhile checking out about reftiing a previously tensioned Cambelt. An enquiry might save your engine or of course it might put egg on my face. Either way it must be worth it.

Roger

[gouldsborough7]

Re: Flat-spot on Hunter/Granada 2-litre DOHC injection

Hi Guys
Took my Hunter in for an MOT today (it passed!), and spoke to the proprietor who is dead keen on Motorsport, sprinting cars etc. When I flagged up my flat-spot problem, straigh away he suggested I swap the standard Ford fuel pressure regulator for an adjustable version.

He maintained that this would allow me to tune out the flat-spot, allowing a bit more fuel to enter the engine during this low level of revs. There is a whole bunch of adjustable regulators on the market, from fancy ones by Demon Tweeks to allsorts on eBay.

Has anybody got any experience in this area, please?

Cheers
Mike

[Dane_Rescueman]

Re: Flat-spot on Hunter/Granada 2-litre DOHC injection

Hi Mike.

I have an injected Pinto in my car running on the Ford/Bosch EEC IV system. My engine has been rebored to 2.1 litres with slightly bigger valves anda torquey cam. I have fitted an adjustable regulator which I bought from Merlin Racing. It will be a similar type to those from Busrton or D Tweeks etc. There are two types. Mine is linear in the same way as the olde Ford fixed regulator but, I can adjust the fuel pressur up a bit to make the injectors pass a bit more fuel for a given timing signal. The other sort is the rising rate regulator. This seriously increases the pressure upon opening the throttle which can improve acceleration. The big but is that the fuel economy suffers which is why I did not fit this type. The kit comes with a pressure gauge so tweaking the pressure up to, in my case 3.1 Bar is easy. When doing this with the engine running, but not under load, disconnect the vacuum pipe, seal it, and then check the pressure otherwise you will be setting the idle pressure to 3.1 Bar with the open throttle, reduced vacuum pressure being ½a Bar or so more.

Mine has worked fine up to now,

[lil_red_roadster]

Re: Flat-spot on Hunter/Granada 2-litre DOHC injection

A few ideas if you haven't covered these off already...

Did you check the crank sensor when swapping items about? Just a thought that the sensor/mounting might be vibrating in a particular rev-range and causing temporary loss of the signal...which will throw everything into complete confusion...a long shot I know.

Also presume plugs, coilpack & leads are known to be OK? They all tend to "go" at the same time and the advice I've had in the past is to change all 3 together. Age rather than mileage can be a factor in this.

Injectors can fail as well...might be one a little "sticky" at low loads? Could be worth a does of Redex to see if that helps.

If you're running the Ford ECU do Gunson's do a cheap fault-code reader? I'm guessing no engine-management light is fitted?

[gouldsborough7]

Re: Flat-spot on Hunter/Granada 2-litre DOHC injection

Thanks Jez
Don't know about the condition of the crank sensor, as I haven't touched that area at all. I take your point about things going wrong due to age, rather mileage. My Hunter has only done 11,000+ miles, but it's 13 years since its original build at Marlin factory.

Having continually studied the symptons over different journey types and weather conditions, I have now reached the following conclusions:-
1) the engine problem is barely noticeable when the engine is cold, and hence I guess more fuel/less air is being metered into the cylinders to compensate, i.e. on choke like carburettor versions.
2) now the weather is warmer, again the problem is less obvious than it was during Winter running.

Think I might leave well alone for the time being - 'if is ain't broke, don't fix it policy'?

Cheers
Mike

[gouldsborough7]

Re: Flat-spot on Hunter/Granada 2-litre DOHC injection

Guys
Think I fixed the flat-spot problem (keep fingers & toes crossed!).
At the previous MOT, two of the young enthusiastic guys in my local garage both said that I needed to junk the standard Ford fuel regulator and replace with an adjustable one. My subsequent Internet enquiries only found regulators around £80, so I was somewhat reluctant to shell out the dosh.

A year later at the most recent MOT, the same guys said the same thing again. This time I found a good looking adjustable regulator on Amazon, for around £37 including carriage from Germany (as it turned out). So I took the plunge and bought it - see photo below.

I made up an aluminium bracket, and fitted it on top of the plastic box (part of the air side of the fuel-injection). The only snag was to get rid of the old regulator on the exit from the injector rail, and in its place installing a simple fitting made by a local light-engineering workshop. This enabled a new petrol hose to be diverted from the rail to the new regulator, and then its exit connected back into the original circuit. A new vacuum pipe in the kit connected the regulator to the original source of vacuum.

I haven't driven more than 5 or 6 miles (only finished the project a few hours ago), but a distinct improvement was noticeable, with no obvious flat-spot. As you can see in the photo (Image 1), there is a pressure gauge, calibrated in metric and psi. I have also shown the old regulator in Image 2 for interest.

Sticking to units I know, I have adjusted the running pressure at tickover to around 30 psi, which seems OK for now. However, I would be interested to know whether anyone can recommend a specific figure to aim for. Any thoughts would be appreciated.

Cheers
Mike

[dogoncrazy]

Re: Flat-spot on Hunter/Granada 2-litre DOHC injection

Mike
Interesting to read that your local garage advised a change to the fuel pressure regulator as this was an area I explored when having similair problems. In my case I purchased a new Bosch regulator but found it made no real difference to the running .This was a non adjustable type that 'plugs' into the fuel rail [assume that yours must have been of similair ] the one on my car is rated at 3 Bar.
Would be interested in comments on whether your 'guys' consider that running aftermarket fuel pump as opposed to the presumably in tank original has any baring on the standard regulator not being able to cope.
Good luck and please keep us posted.

[gouldsborough7]

Re: Flat-spot on Hunter/Granada 2-litre DOHC injection

Hi Alan
The original cylinder-shaped regulator shown above was fitted to the rail at the exit end. My local light-engineering firm cut off the cylinder and silver-soldered the remaining stub and bracket onto a piece of suitable tubing.

All I had to do was to re-fit the stub into the rail, and connect up some new petrol tubing onto the after-market regulator, and complete the original circuit on return to the tank, plus of course connect up the vacuum pipe.

I intend to run the new regulator at around 30psi, which the engine appears happy with (unless someone tells me to do different), and will feed back my experiences to the Forum.

Cheers
Mike

[Dane_Rescueman]

Re: Flat-spot on Hunter/Granada 2-litre DOHC injection

I installed the Ford/Bosch EFi on my pinto. The basic system is similar on the DOHC although more inputs are used to the EEC IV module. The original pump in the 1988 Sierra donor for my engine used an out of tank pump. It was fairly high capacity and in conjunction with the injectors and fuel pressure regulator was designed to operate at about 2.1 Bar. At idle the vacuum adjusts the regulator down by .5 Bar to approximately 1.5 Bar. The injectors work on a timing pulse from the EEC IV. It is recognised that if one increases the fuel pressure then the injectors are able to pass a little more fuel for each pulse.
I now have an adjustable regulator from Merlin Racing which I run at 3 Bar with vacuum disconnected - so idle would be around 2.5 Bar with the vacuum connected.

It is important that the inlet to the HP pump is the correct size and there is a free flow of fuel to the pump. An in tank pump will have all this taken care of of course although in an old tank with no baffles can still cause cavitation even with reasonable fuel contents.

My engine is bored to 2.1 litres with slightly bigger inlet valves and a high torque cam. The engine can be slightly choked with the original intake tract so I have had to be careful to allow more air and a smoother passage for it. I'm not there yet but the prototype system is working OK.

Goos luck with the new regulator. Only increase the pressure in small steps is the advice I have been given.

I have the printout of all the Bosch fuel pumps. The capacity, rated pressure and lockout pressure are all very different as is the maximum fuel delivery rate from the injectors (167cc/minute/each in my case). Once one gets one's head around the various sums, sorting the system becomes easier!!
Or "B", Hmmmmmm aargh phut!