Will check this over the weekend - going to replace the coil regardless, though, just so I know it's not at least contributing to the problem... I did wonder this initially, but all injectors have been cleaned and I've even tried swapping them around without it making any difference
I used to have a problem like this when my coil was playing up. Is it a mk3 style coil pack? Yellow spark is not good. If it is that type of coil, you can test resistances between HT an pin 15 IIRC. Never found a coil at 4kohms, even new. Anything around 2.6k is bad. Found it here.
Just picked up a new Beru coil - wanted to cross it off the list! I'm away until Monday night, but I'll fit it then and see what happens
Wasn't there a link that described similar problems that were caused by a faulty ignition switch of all things??? See if you can dig the link out using search, i'm sure someone had similar problems caused by the ignition switch. __________________
Thanks for the suggestion, but I don't know how this could affect just one cylinder Willing to try anything, though I've fitted the coil and it made no difference - #1 still won't fire after a cold start and only gradually begins to work as the engine warms up Yet to try a leak down test - is this worth my while... Surely all that's left now is a headgasket problem
is the spark any better with the new coil? how are your engine earths? early cars have a poor box earth design. the -ve wire from battery terminates at the upper gearbox mount bracket arm thing, which is not a great place. later mk2 and mk3 switched the battery -ve to the rear engine->gearbox mounting bolt, it has a stud on the end where the cable attaches. mk3 battery cables are well worth fitting too much better than the mk2 cables. you may have to make up a bit of chunky wire from the battery -ve to the battery tray earth stud, mk3 cables dont quite reach it. if you can find one, B4 passat has mk3 style cables and it reaches the stud too. disconnect the dizzy plug to rule it out, ecu will switch to batch fire mode. if it runs fine then yep, you need a dizzy, if not its not the problem.
It's in a Mk3, but has a relocated battery etc - all done very well with heavy gauge cabling and has never been an issue in the past I've tried unplugging the hall sensor and it makes no difference. Also removed the dissy this morning to check for oil leaks, but all looks healthy and the o-ring is new. I've just noticed that #1 is hardly firing at idle even once warm... I had thought it was because it sounded stronger than when idling cold, but it's actually only firing when revved and perhaps occasionally during idle (idle is slightly lumpy - sounds like a cammed engine) Pulling #1 lead when warm actually makes no difference to the idle. As soon as you rev the engine, though, it seems to pick up all cylinders. Power still seems down when driving, so I can only think #1 is under-performing right across the range. There's also a bit of stammer at around 3-4k when cruising on light throttle once warmed-up. Very close to giving up now... Not sure if I try a dissy as a last resort, but I'm really doubting this is the cause - nothing seems to help! All I can think is it's a weird head gasket problem, but SURELY this would be reflected in a compression test and the compression on #1 is 210psi
- - but for a $10 vacuum gauge A former boss once asked me to examine his carburettored 350 Chev powered 80,000 mile station wagon, which ran fine for ~30 mins after each tune up then 7 cylinders thereafter Conducted the standard tests including h.t. system, compression, etc etc - hmm, noticed #3 plug had oiled up - fitted new set, ran bonza for ~10 minutes then back to 7 again - attached a $10 vacuum gauge, sho 'nuff the bloody needle bounced every which way, sure sign of an intermittent vacuum leak - removed the inlet manifold to find a casting flaw where the #3 runner face squishes the intake manifold gasket against the cylinder head - a little well peened 1/8" 6018 rod @ 120 amps to fill the flaw, carefully filed it flat, new gasket & plug and away she went (for those unfamiliar with 350 Chev's, the intake manifold gasket prevents the oily crankcase fumes circulating around the cam followers and pushrods from escaping to the atmosphere; the flawed #3 runner drew those fumes directly into #3 cylinder where they soon oiled up the spark plug ESPECIALLY when the engine was idled excessively or being driven, as most station wagons are, delicately) Boss later said he'd bought it the wagon new, complained many times when it was under warranty, had numerous scopes run over it etc etc but all fixes were temporary[:^(] This yarn is an effort to brighten your spirits and encourage you, and/or others depending how your diagnostic skills work, to think in or outside the square We're talking physics here, the laws are immutable, its ALWAYS something simple, and we tend to either assume too much, not enough, or there's a combination of factors, sometimes even intermittent, which throws us off the scent (mea culpa, ask how I know these things) Is there a local road dyno operator with a scope AND skill that the engine dynamics may be monitored, data based even, under load? p.s. I miss The Rocks
earth was a long shot really, as tristan points out unlikely to effect just the 1 cylinder but bad earths can do all kinds of funny things! as i say though, is your spark any stronger with the new coil, is it nice and blue now? think LCT might have the answer though, think its time to go thru the inlet tract with a fine tooth comb looking for vac leaks. have a look at your PCV valve if its still fitted, if in doubt disconnect the vac pipe to it from the inlet and cap it off, see how it drives. also take off and cap the brake servo pipe, if it improves then look at the pipe and servo for leaks. might be worth doing a fuel pressure test as well? from elsawin: Start engine and run at idling speed. Check fuel pressure specification of approx. 2.5 bar Pull vacuum hose for the fuel pressure regulator at the side of the inlet manifold. The fuel pressure must increase to approx. 3.0 bar. Switch off ignition. Check for leaks and holding pressure by watching pressure drop on gauge. After 10 minutes there must be a residual pressure of at least 2 bar. If the holding pressure drops below 2 bar start engine and run at idling speed. After the pressure has built up switch off ignition and at the same time clamp-off the return pipe on fuel manifold. Watch pressure drop on gauge. If the pressure does not drop, renew fuel pressure regulator. If the pressure drops again: Check fuel pump non-return valve Check pipe connections, O rings on fuel manifold and injectors for leaks
Thanks for extra suggestions - really appreciated Fuel pressure is perfect and entire system is brand new! The vac leak theory does have some merit, as the engine does idle at 1050rpm when warm, which would suggest a vac leak... I've never looked into it further, though, as I've always assumed the ITB kit is causing it - plus all the lines are new. There is a plumbing setup underneath the manifold to incorporate the ISV, though, so perhaps there are issues here. I'll pull the entire setup off on Saturday and go over it... Otherwise, I guess I'll try a dissy, and if that doesn't work, I'm going to flog the setup and get a 24v!!!! Sad really, I've had a 5 16v engines and they've all been fantastic for years until this one...
ah forgot it was ITBs, doh. totally different kettle of fish checking for vac leaks but im sure you'll figure it out eventually. its got to be summat simple, just a case of finding out what!
Vacuum snoop Firstly, assuming your ITB's have a common vacuum line to feed the brake vacuum booster, hook up a gauge Depending on camshaft and tuning specs, volume within the hose itself, and whether the gauge has a restrictive orifice to prevent wild oscillations, the needle should hold steady around 19 - 20" with regular fluctuations as each cylinder draws If not, and assuming one cylinder only is being affected causing a regular once-per-two-revolutions swing, take an aerosol can of brake clean or similar volatile-but-not-too-much fluid, shove a piece of small diameter plastic or rubber hose over the short extension squirter they come with and, very carefully nuzzling the end of the extended hose against the manifold gasket or any where else leaks might exist, direct a small puff of brake clean at that area Careful! obviously we don't want a conflagration! best have a buddy at the wheel plus fire extinguisher and/or garden hose at hand I've also seen diesel engine starting fluid used for this trick, but being ether based it's really inflammable and demands extreme caution - a positive being that unlike fluids it evaporates extremely rapidly, so any ignited gas quickly disappears unless cloth or a similar material has been soaked A vacuum leak will allow a whiff of flammable gas into the manifold and engine revs will temporally rise A safer but messy alternative is to load up the oil can with ATF or similar lightweight oil and liberally squirt it wherever a leak might exist, which temporally clogs the gap again causing a rise in rpm Don't forget manifolds crack, especially where the flanges transition to body proper - - once saw a colleague squirt oil all over the dual carb bodies and manifold of a troublesome TR4, you literally needed a magnifying glass to see it, but yep, it was cracked That particular car had driven many people to drink, as the miss relied on a subtle combination of underhood temperature, throttle application, and humidity A marginally effective fuel mixture, to one or more cylinders, plus a weak link in the ignition system can also "complement" one another to create a miss where one factor alone would not Frustrating as the process may be, a "Eureka" moment always rewards perseverance
ITB's... hmmm have you made sure they are all balanced? I have read most of this and the other thread you had and did not read that it was on ITB's, I thoughout you were running standard plenum Digi setup? What management are you using?
Ooh, watch this one - - Never assume brand new parts will function as advertised! So long as an engine started and ran, our rule of thumb was never replace anything unless diagnosis has either proven it faulty, or every other critical or influential component has been exhaustively tested and one's instincts say "yep, it's gotta be - - " and still be prepared for disappointments as they WILL happen What does the engine FEEL like? Don't laugh, some folk develop inherited gifts which have little rational explanation - - for instance, depending on their health components may appear in different colours Nonsense? not to one very successful troubleshooter of my acquaintance Re fueling, has the system been tested dynamically, ie simulating actual running conditions, as possible? An injector spray pattern which appears acceptable at atmospheric may not when operating under vacuum, as spray pattern, atomisation, and vapourisation are all affected, for instance the vapourisation temperature is lowered, which in this case assists combustion - - but you get the picture - -
