Im new and need some advice please

Post by **tony-de-whitt** » 29 Jan 2007, 11:40

Hello.

Im new to these type 25,s and this forum so be gentle.
ive just bought a 1985 1.9 litre petrol fuel injected van. engine code starting (DH) ive been told this is fuel injected but havent had a good look at my haynes manual yet.
Ive just emigrated to australia, and have got a couple of questions for you clever people.
Firstly the backfiring, am i to get used to this or is there something i can do to reduce it?. There are no exhaust leaks as ive had this sorted. It pops and backfires on engine breaking, ie its fine accelerating but as soon as you loose off the gas it backfires. any ideas.?
Next, is there an alternative coolant that is sold in oz as i cant find G12.
Finally, what do i need to know about fuel injected as ive no idea how it works, ive been told there is no carb so presume the fuel must be pumped straight into the engine, anyone care to enlighten me on this new technology(im used to old type 2s).

thanks in advance
anthony

Post by **madmyk** » 30 Jan 2007, 00:37

Hi Tony,

Welcome along. 'Fraid I cant help you with this one, but just didn't want you to feel ignored, I'm sure someone will be along soon that can answer you, but have you tried checking the old threads? Perhaps search under your engine type and see if there are any similar snags? Same with anti-freeze Q.

Hope this helps, or at least gives you something to try in the meantime

Best of luck,
Myk.

Post by **Andy syncro-nutz** » 30 Jan 2007, 01:40

Fuel injectors work by the princable of a crystal (pezo) and electricity! Pezo crystal destorts when energized by electricity! Thus acting as a valve! When fuel is put under pressure behind the crystal and it is energized it will allow the fuel to pass to the engine! (Just a very fancy automatic like water tap)

The clicking you will hear coming from them is that little crystal inside! This all takes about 2.8 milly seconds and about 1.9msec's at full throttle.

Post by **Andy syncro-nutz** » 30 Jan 2007, 01:44

Oh and have you ignition timming ckecked! Sounds like it's too avanced.

Hope this is of help you jammy git in OZ!!!

Post by **HarryMann** » 30 Jan 2007, 02:04

what do i need to know about fuel injected as ive no idea how it works, ive been told there is no carb so presume the fuel must be pumped straight into the engine, anyone care to enlighten me on this new technology(im used to old type 2s).

Anthony, Hi there,

[Too retarded or too weak usually, for just light popping back)]

You probably need a Bentley!

not a car, but the manual, as its much more detailed than the Haynes. but they're about £55 here (JustKampers) maybe try asking for 2nd hand one

Anyway, it does cover the DH I believe, not the DG which most are here.

The injection system on the DH is I think a Digijet, much the same as the 2.1 DJs (the later MVs are Digifant)

This is a system that controls the fuel injection, but not the sparks, which are provided courtesy of a distributor with cent adv. and vacuum adv/retard unit. A Hall sender in the dizzy tells the Ignition Control unit to produce a spark and that unit fires the primary of the HT coil, rather than the conventional Low Tension circuit breaker points - so don't play with the ignition as freely as you might have done on older cars. So that's electro-mechanical, works fine, but is not integrated directly into the ECU (Engine Control Unit, brain) on your DH.

The injection is controlled by the ECU, which listens to a few signals, mainly the AFM (Air Flow Meter, big black box, right rear of engine bay; a basic sprung vane/potentiometer device). Also listens to temperature senders in coolant and in AFM , throttle position (demand signal) and opens the injectors up (non-sequential) so that they flow fuel into the ends of the manifold quite near the cyl head ports. These are pressurised with fuel form the fule pressure regulator (honest!) which is fed by the fuel pump. The pressure regulator (about 30psi) sits atop the engine, as also does a mysterious silver cylindrical thing called the Idle Stabiliser Unit, controlled by a black box full of relays that people argue over all the time, like where is it? On the roof, under your seat? No! Behind the r/h taillight or on the l/h eng. bay firewall. Anyway, forget about that for the minute, the control unit is wherever the wires lead to on your particular vehicle

So get the idea? Two fairly good (when they're new) but independent systems to sparking and fuelling on the DH/DJ. Lots of nice thwacky sparks, and suitable fuel quantities if the engine's turning and the ECU's reading the airflow into it (correctly).

========== ==================== ==============

Popping back on the overrun eh? Or really backfiring bad ?

You know the former is usually either a weak mixture or somewhat retarded ignition? The weak mixture burns slower, and may still be burning when the exhaust valve opens, and a holed exhaust or air leaks in the inlet weakens the mixture.

You've checked the exhaust for leaks it seems, as this can cause weakness.

Have you checked all the hoses on the air inlet side from the AFM through the manifolds for leaks? Even hidden splits? Pipes that feed the dizzy, the ISU etc.
Start there and then think about ignition later, unless the ignition has been set (heaven forfend) recently and if so correctly. You could check your advance/retard pipes first, and look inside the dizzy, just to make sure its not a total bombsite!

Being 20 years old ? nw, and these systems having a reputation for bad earths, and there are a lot of them, start thinking along those lines too. All are suspect, but don't exactly fit your current symptons, but don't worry, they will soon enough

One connection always worth checking si the T2 temp sender which is under the thermostat on 2.1 DJs. the output of this little devil should really eb checked against what Bentley says (a Temp~Voltage graph), but don't break the plastic? thermostat housing too soon, or when away from home, eh?

Good luck, someone will come along and spill more beans pretty soon I expect, but for now, hopefully a few to pick up on..

Post by **tony-de-whitt** » 30 Jan 2007, 07:06

Thanks for all the replys.

what should the timing be set at for my engine?
I seriously need to spend some time in the engine bay to see whats what, a lot of what has been said so far seems a foreign language to me but i will get there.

thanks again

anthony

Post by **HarryMann** » 30 Jan 2007, 12:32

You need to read up and re-read how the thing works first, looking gaumlessly into an engine bay won't help too much to start with... I'm a past master at that, so i know when i don't know. You seem to know you don't know so get a Bentley manual if you are going to keep this vehicle and/or can't find a good VW WBX technician/mechanic around your way. If you can, then use them, you might have an exhaust valve burn driving it weak or retarded for long.

For instance, presumably you'd recognise light pinking around town, and know the consequences of its corollary, high-speed detonation - if you answer No, then best get it to a VW shop. Just trying to help, you understand but messing with ignition timing without knowing instinctively whats wrong, is a bit like going Scuba Diving with an empty bottle of oxygen, but not quite so life-threatening

Though it sounds like you do know the symptons of popping back under light throttle/overrun and have been around motors quite a bit... so here is the guff you asked for.

=== Before getting all this checked/reset === you should really quickly physically inspect that the vac/adv. and cent. unit 'seem' to be working OK, e.g. no obvious leaks in hoses, blockages at pressure tappings, and no gummed up dizzy. Because unless someone has been swinging that dizzy around lately, that's not what's wrong - it'll be the vac or cent. unit, so don't go swinging it around unless you know for sure it needs swinging! It might stop the popping back but lead to over-advance under load at speed if the dizzy's a mess.

== Here goes: timing a DH ===

http://wiki.80-90.co.uk/index.php/Petro ... 1.9_Timing

Post by **HarryMann** » 30 Jan 2007, 14:34

P.S. All above presuming it's backfiring through the exhaust and you don't mean spitting back through the inlet, a different thing entirely and more likely under load than off-load.

And how bad is this backfiring? Popping-back under decelaration or loud backfiring? Only after a fast run or at any time you light off?

Post by **tony-de-whitt** » 30 Jan 2007, 21:27

Thanks for the reply.
As you say everyone has to start somewhere.

Its definately not backfiring/popping under load , it seems to be running really well. Its not really loud but noticeable from the cab with the windows down.
It happens at any time i light off, seems worse in lower gears.
If im stationary aswell, if i was to accelerate not in gear it still pops a bit as its slowing down.

Post by **tony-de-whitt** » 31 Jan 2007, 10:39

Ive realised today that the noise is not there when the engine is first fired up and is still cold. It seems that when its warmed up it starts. If its any help the bloke i asked the bloke I bought it from and he said the noise has been present for a long time. Bearing in mind this vehicle was regularly serviced by an (australian) VW mechanic, is there anything that someone could have fitted to make this noise, just a thought. I think i will take it to a VW specialist tomorrow just to get the timing checked.
any more info greatly received.

thanks in advance