(no longer)Intermittent rough DOHC

[Copey]

first off about the car, 1990 Sapphire GLSi Manual box with 103k on the clock, serviced regularly, most recent was 3 months ago, oil, filter, plugs, leads, rotor arm, dizzy cap etc. Also the car doesn't smoke all that much compared to most DOHCs I have seen.

Anyway, recently my car has been a pain at low revs, its very rough, hesitates and judders (below 2500ish) and the tickover is very rough, but its all intermittent, its always a bit rough from cold but once driven a couple of hundred yards it is normally fine, but occasionally you will be doin say 30 in 4th and the car will have a couple of seconds of feeling almost like engine braking, its never constant, just little blips, like if you were coming off the clutch to go down to 3rd is probably the best way I can describe it and the idle will normally sit bang on 1000rpm but will occasionally drop to 500 for a second then jump up and idle rough around the 700 mark or sometimes (no matter what the engine temp) it will just conk out completely, always starts back up straight away and the car accelerates and drives perfectly fine otherwise.

I just wondered what anyone could be the cause/s? does the idle control valve have any effect at revs? or is it just at idle? could the TPS be on its way out and causing any issues and giving a false reading occasionally? I have also noticed a gargle through the heater matrix recently which is normally a sign of an air lock somewhere, though the car doesn't overheat at all, though I will flush it out tomorrow and re-fill, could this be causing the engine temp sensor to be giving a false read every now and then? Could the fuel filter be getting blocked and causing fuel starvation at low revs?

Any other suggestions on what it could be? and how would I best test sensors?

I am very sorry for all the questions, I am used to ol' pintos on carbs, injection is a bit new to me! (even this simple barn yard type)

Thanks for any help you can offer

have some pics of Sierras in action

[retrobarmy]

Some engines can leak pressurised coolant via the (water cooled) inlet manifold gaskets into the inlet valves due to either loose manifold studs/nuts or breakdown of the gaskets/seals. The leak doesn't show externally. A tell tale is an occasional hesitation on start up due to hydrostatic lock caused by coolant in the cylinder and slight coolant loss.  Gasket failure can also lead to weak mixture on affected cylinder/s.

[Copey]

cheers, i will check that out, though i havent noticed the coolant level dropping at all, but it may be very slight, thanks

[vitesseefi]

Crank position sensor?

Nick

[Copey]

it could be another option

[gavs1]

defo cps mate, my festa was playen up the same as ur is and ended up being a 7 quid cps

[retrowrongun]

Check compression on it mate as these things eat piston rings and bores for breakfast from personal experience

[ejenner]

The symptoms sound like the CPS could be a possibility although I've got no experience with the Ford setups. CPS issues in my experience also cause failure to start.

The description sounds to me much more like a fuel problem. Blocked fuel filter, fuel pump on the way out or one of the load sensors (such as TPS) not giving a good signal to the ECU.

[Steve]

Funny how this has popped up as the DOHC in the Viva decided to idle like a pig yesterday when I moved it for the first time in two weeks......I was gonna lean towards fuel pump/pressure issues but that is just down to me knowing how curse word my current setup is but failing CPS could also be a likely culprit

[Copey]

i will check all of the above this afternoon, well, all but the fuel pump as thats hidden under the fuel tank! stupid design! its not noisy though so hopefully ok, if none of the sensors sort it i will check it

cheers

[Copey]

cleaned out the ISCV with car plans version of gunk, blew it out with an air line, let it dry and sprayed with silicone grease, good as new

[Copey]

righty, couple of weeks after my last post the problems started again, took ISCV off, cleaned it out again and it did nothing, bought a brand new ISCV but the problem is still there, exactly as before, keeps trying to cut out, wont accelerate smoothly at all, when its at idle it will drop to nearly cutting out point and shoot up to 1500 and instantly drop back down to nearly cutting out and then back up and so on, its gotten to the point where i don't want to drive it for fear of it doing some damage, which is a pain as its my daily car and only car on the road right now!

theres no water loss, no oil loss, it doesnt smoke a lot and there is no signs of water and oil mixing, no overheating issues...i am now clueless

i miss carbs!!

[retrowrongun]

Have you compression tested it like I said earlier

[bortaf]

Check the fuel pressure reg isn't stuck open and your low on fuel pressure, i doubt low comp would give a problem that comes and goes TBH.

[retrowrongun]

Mine did and was down to coked up sticky rings and egg shaped bore on 1 cylinder ,bought a second hand motor and guess what ,yep same thing hahaha

[Copey]

well, mate posted me out a new MAP sensor as he thought that may be the problem and all seems well

[SmokeEm]

Had a similar problem with my daily recently. After spending a fortune trying to sort it out it turned out to be a hairline crack in the ceramic on one spark plug!

[sarkie83]

major thread resurrection, but did you ever get to the bottom of it?

as the dohc in my granada has been a pain for about the past month. most of the time it will run fine, bit 1 out of 3 times i drive it it cuts out out. (it seems to especially like busy roundabouts at rush hour!) if you go to re-start it, it will crank but not start. Go wiggle brown wire attached to the negative battery terminal and bingo, it fires up and off you go. Looking through the wiring diagram in haynes that directly feeds the ecu negative terminals. Originally i thought it was a dodgy battery connector, so replaced it - same thing. I went through the loom back to the ecu looking for damage - nothing, re-taped it, same thing. Tried a different battery (incase dodgy voltage was causing it) - same thing.

Today when i was driving it, it was horrible, did the same idle thing your were describing. Then from 30-40mph it would not accelerate smoothly, was very jerky.

[chinno204]

I worked at a Ford dealer when these were new:
Idle problems were usually caused by hose from crankcase breather valve (P.C.V) burnt through, the valve is under the exhaust manifold & there's a short section of hose onto a metal pipe, the hose would go crispy due to heat & collapse, a new section of hose with a heat resistant shroud would sort it out.
Rough running, hesitation & kangarooing usually down to water in the M.A.P sensor, we used to remove them & leave 'em on a radiator to dry out overnight.
Cutting out & non-start usually caused by dodgy C.P.S, either breaking down when hot due to age or damaged wiring after being caught under the oil filter during an oil change.

Maybe one of these will help?