Hey all,


Trying to sort out a little glitch with a 1700 Zetec-SE VCT. It general runs a bit rough, but when idling and generally driving round with not much throttle the engine runs and sounds fine, but under load or with more than a little throttle the engine sounds like its suffering from pre-ignition, reasonably loud (depending on how much throttle is applied).

Its not rev dependent (i.e. if you build up the revs with little throttle, i.e. with a bit of momentum or down hills etc. it is still quiet), its more throttle dependent.

Plugs were matte and the electrode was a caramel colour, but no signs of plug damage. They were NGKs but the wrong type (the were the normal LPN or something similar) so I have swapped them for platinum plugs which were listed for the engine.

OBD showed that the ignition was roughly 33 degrees advanced at idle, so I replaced the MAF as it was ford branded and probably on the engine since new (engine has done 113k and 11 years old). Left the battery off for an hour or so just to reset things.

So far, no difference. The codes previously pulled were:

P1131 (Ho2s not switching)
Diagnostics showed from start up on open loop that the HO2S started around 0.4v then dipped off slowly 'til it was around 0.02v. Wasn't switching either.

P0131 (cylinder one misfire)
Plug looked no different to the others to be honest.

Engine is reluctant to start, idles at 1k but is very lumpy.

The headgasket is leaking slightly on the chamber/coolant area, and I intend to do this as soon as possible but i'm looking to try and sort this ignition issue out before looking at a potential headgasket failure.

The Ho2s looked a bit aged but I'm not convinced that it could cause a lean condition enough to cause the pre-ignition/misfire?

Also not wanting to go down the route of 'why not try hi octane fuel' as i'm more concerned at why the car isn't running right on 95RON when it should?

Any advice/comments welcome as its getting to be a bit of a pain!!

Thanks

 

hego prob effected by the misfire mate, if it getting soaked in petrol it wont work. zetecs suffer from coil pck failures and are reli common and cyl 1 and 4 are the usal faulty cylinders. but if the head gasket leaking it could be losing compression. maybe worth trying a coil mate

 

I would think that if it weren't for the pinking, coils would usually give a complete hesitance or flat spot. The engine will rev as free and easy as you like, not a lot of power loss, just the pre-ignition noise.

I've been keeping it off noise as much as possible, pretty sure its blew the gasket but its not done enough damage to screw the plugs up so it can't be as bad as detonation but still seems a mystery.

Will have to try another 02 sensor I think, any other ideas welcome.

 

what hego mate, post or pre cat?

 

Pre, its a '98 theres only one bank. Fixed an 03 clio that had a goosed upstream o2 sensor that was causing a lean misfire but symptoms were totally different as the car runs fine on light throttle, its mainly the pinking thats the only symptom (I put the poor start down to the HG).

Every engine is different (from manufacturer to manufacturer) so not so sure if just the HO2S is causing pinking.

Reason for the MAF was that I thought it could be the only thing causing the ECU to advance the timing so much.

 

possible hego but they usually neva cause pinking, wudnt thought it being the maf mate. im a tech at a ford dealer n neva had maf probs. had problems with the main injector multi plug (n/s inner wing) they get damp and cause funny symptoms. mite b worth checking that. u checked fuel pressure and changed your fuel filter? could b fuel pressure related, that would cause the hego to run lean and think its faulty, cyl 1 furthest on fuel rail so wud get the lowest pressure. fuel pressure wont give a fault code

 

When I pulled the injector loom 'rail' off earlier, I released the pressure with the nipple and there was a little squirt so theres some pressure getting to the 1st injector. Does the fuel pressure show on OBD2? Never really needed to look into it before, not sure about the fuel filter haven't had the car long enough.

Would fuel starvation affect the ignition timing? Thats whats concerning me the most, as it seems to be bizzare that it wants to advance so much??

 

wont show fuel pressure on obd mate as its just a mechanical pump. it mite give a squirt but it mite not b enough pressure on demand. if the cars running lean the ecu will try to do what it can to richen it up. id def change the fuel filter mate (they easy to fit and cheap). you have to do a fuel pressure test on the rail mate, after that mileage the pump mite b tired out not being able to give the pressure when needed. would cause a lean misfire and b ok at light load

 

Ok no problems, you've been a super help so far.

Quick questions though, assuming the filter is inline near the tank as of most cars, and would all this still be affecting the ignition timing?

Thanks

 

yea mate, if the car runs lean the ecu will try and richen itself up mate. the hego will adjust the other sensors including the maf. its a inline filter mate, passenger side in front of the tank held on by a metal clip. id change that if it still does it check your fuel pressure buddy.

no worries, hope you sort it fella

 

Ok no problems thanks will try and sort it tomorrow, will post up the results on here (always helps those who are having a search).

Thanks for your time much appreciated.

 

Changed the fuel filter, the old one was well gone (rotten).
Added a little injector cleaner.

No new fault codes but still running rough on idle and pinking intermittently (when standing).

Heres some of what I recorded at idle:

Throttle position - 18%
Engine Speed - (varied between 950 and 1050 rpm)
Calculated load - 47% - 57%
Ignition Timing - advanced between 6 and 10 degrees
MAF flow - approx 4 g/s at idle
Fuel trim bank 1 - approx 20% rich
Ho2s - switching between 0.2 and 0.6volts
Coolant temp - 55 degrees
Intake air temp - 20 degrees


Would coil pack be causing issues now?

 

It's a reli common fault mate, I'd try 1 mate. Wud cause the probs ur gettin fella

 

Quick update, tried the coil pack - no difference.

Been suggested the TPS could be faulty and over-reading? Is 18% at idle a bit off the scale? Going to investigate it a bit further in the morning though.

 

Update:

After a full top end strip down, the cylinder head gasket appeared to be severely split between cylinders 1 & 2 (area of about 7mm x 15mm), but there were no signs of the missing section anywhere in the cylinders. Excessive amounts of liquid gasket/mastic on the mating faces of the head & block, along with missing gaskets replaced with said sealant goop and several other things including missing bolts, tippex timing marks on the cam sprockets (even though they are adjusted when the cams are locked? Pointless?) and copper K seal type crap in the coolant shows signs that the head has been bodged previously.

Replaced all gaskets and head bolts (althought they don't neccesarily need to be changed - didnt trust the previous by the state of the rest of the stuff) skimmed the head just to be sure and timed the engine up to what seem to be correct and the coolant is no longer pressurising and the pinking seems to have stopped. drove steady and no more than 2.5k revs on the way back but up the hills doing low revs in high gears it pulls well and is pretty quiet.

So far so good, will add some more information later after I've taken it for a good run to make sure the ECU has recalibrated correctly.