Club 80-90 Forums

me new crewie has a 2.1 and has a small problem. it is a low mileage engine and the crewie was bought off a good mate so i know the engine is spot on. it has been driven less than 4k miles in last 2 yrs.
on starting up for my commute it stinks of petrol , when i get home 45 mins later it still smells bad but not quite as bad. if i floor it (have only tried it in 3 + 4th) and bury peddle to floor quickly , it backfires very loudly and not just once but in quick succession like a machine gun. almost as if every cylinder is doing it.
can i assume/guess it is over fuelling and the back firing is excess fuel being burnt off in exhaust ? any ideas ? I have done a search and the senders appear to be a common fail item,as does the earths/wiring. would this fit with my problem.(if it is let me know where senders are and wiring location)
also idles very slowly when cold , almost as if its gonna cut out and not quite firing right. same fault or just coincidence ? reckon the idle could have been wound out to lower emmissions ? I know me mate wouldnt have stiffed me - he just used it for a few shows every year so probably lived with it.
waterboxers are new to me so explain everything slowly!
cheers Elvis

ELVIS wrote:me new crewie has a 2.1 and has a small problem. it is a low mileage engine and the crewie was bought off a good mate so i know the engine is spot on. it has been driven less than 4k miles in last 2 yrs.
on starting up for my commute it stinks of petrol , when i get home 45 mins later it still smells bad but not quite as bad. if i floor it (have only tried it in 3 + 4th) and bury peddle to floor quickly , it backfires very loudly and not just once but in quick succession like a machine gun. almost as if every cylinder is doing it.
can i assume/guess it is over fuelling and the back firing is excess fuel being burnt off in exhaust ? any ideas ? I have done a search and the senders appear to be a common fail item,as does the earths/wiring. would this fit with my problem.(if it is let me know where senders are and wiring location)
also idles very slowly when cold , almost as if its gonna cut out and not quite firing right. same fault or just coincidence ? reckon the idle could have been wound out to lower emmissions ? I know me mate wouldnt have stiffed me - he just used it for a few shows every year so probably lived with it.
waterboxers are new to me so explain everything slowly!
cheers Elvis

Well I have just recovered from a different kind of problem on my 2.1 DJ. However I learned quit a lot (if you can call about 10% of what you really need to know quite a lot) about the Digijet system. As far as I can work out the injection is tied up with the signal from the Hall effect sender in the distributer as far as timing is concerned. Although leaning in the direction of a common rail rather than direct injection. The amount of fuel injected is I believe governed by the Air flow meter so this is a posible problem area. In addition to this there is the cold start device (whose exact name I can't remember) which is connected between the air box and throttle housing and vibrates presumably at the behest of the temperature sensor on a mark space ratio thus metering air and effectively setting the fuel/air ratio or mixture strength for cold startiing. I guess this is the equivilent of an automatic choke. There is also some interaction between the iinlet manifold vacuum and the fuel pressure regulator. Plus a couple of switches on the throttle. most of these talk to the ECU which seems to lord over the whole caboosh. So there are several areas which in my opinion could cause your problem of apparent excessive richness. In a matter of hours I bet you get suggestions for quite a few other posible fault areas from all the other students of varying levels in T25 diagnostics some contradicting others. Do you have the bentley manual? If not I would suggest you get one as it knocks the Haynes manual into a cocked hat.
Sit back and read the posts ...
Regards
Ken

If the idle is too slow when cold, I would suspect the ecu temp sender, with two pin plug on the side of the thermostat housing.
Unusual though, as they usually read too cold, and quicken the idle.

With the backfiring it sounds to me like an ignition fault, do you feel a slight hesitation before the backfire, as this would indicate no spark, which would push the unburnt mixture into the exhaust, then detonate when sparking resumed, you would feel it though, and these engines are very smooth, and shouldnt be lumpy like a deisel

A poor spark or broken hall sender unit could cause these symptoms, it is the small electrical thing on the firewall with one oblong plug at the bottom. And would cause poor tickover.

Could be a plug, if you wizz out the four plugs, they should all be biscuit brown, and very very similar, identical really. If one was very slightly different I would suspect that particular plug, or lead as the fault.

If the system was overfuelling, ie the pressure regulator was causing in excess of 30 psi, it would be running rich all the time, and use loads of fuel, and black smoke on hard acceleration, no visible smoke should be seen (water vapour accepted) when revving a warm engine. This particular problem would not cause a smell of petrol around the engine unless there was a leaky fuel pipe.

Other causes of backfires is a leak in the exhaust ( I think)

This is not a problem I have come across myself so the above is speculation.

as Ken Simmonds points out, there are tests for each individual
component of the injection system both in Haynes for DJ engines, and Bentley for the very similar MV cat equiped 2.1's.

If it were my engine, I would start by looking at the plugs. Then temp sender, ( which is worth replacing anyway), then see where that leads.

Good luck.

simon.

think i may of got somewhere(quickly)! matey has just emailed and said that it is fitted with some sort of sprung loaded rotor arm that cuts spark when it reaches certain revs , obviously all this unburnt fuel has to go somewhere! Will let ya know how i get on tomorrow!

I had a 4800rpm one on mine, which would cut in at an alledged 145kmh when it was new, but this top speed reduced over 3000 miles to 125kmh. When it hits the top rpm, it judders like it's fooked, but I never had a backfire.

Now got a 5400 rpm one, havent set that off yet. Seen 100kmh in 3rd, still going. (no rev counter)

cheers Si! am converting over to gas very soon so will treat it to a new set of plugs/cap/arm/leads and senders for piece of mind anyway. engine runs really smoothly otherwise and i know it has low miles and i know the guy i bough it off is a good egg.Baxter is on holiday now - do GSF sell best quality option for bits i want ? dont want to end up with "pooh" ( i have read the GSF senders are "pooh" so they will deffo be VW)

theres allways me to buy your bits off you know i work in a motor factors you wassak

The gas will totally by-pass the injection system, unless it's the posh expensive one.

Just stick with plugs, leads, cap and rotor.

im cool with how the gas works but want engine in tip-top nick. will let ya know how i get on tomoz

backfiring (thro exhaust) is usually late/long burning, often caused by weak mixture... not rich.

Also excessive retard (e.g. late spark), hole in inlet manifold or exhaust manifold / pipes, partic. on overrun.

Suspect as Simon says to start with, get leads, rotor arm, hall-sender checked, often a quick checkover with an ingition analyser is best, gets to the bottom of problem as to whether sparks are coming at right time, powerful and consistent etc and all resistances down the HT lines roughly right.

syncrosimon wrote: If it were my engine, I would start by looking at the plugs. Then temp sender, ( which is worth replacing anyway), then see where that leads.
Good luck.
simon.

See told you so! (re all the other input) Anyway The reason I described my DJ problem as unusual is that i went through the usual steps to diagnose my intermitent dead motor syndrome and the result was a little surprising. I am certainly not suggesting yours is the same but:

The motor died on the road after anything between 4 and 57 miles but would start and die again imediately. The running time being proprtional to the resting time. ie wait for an hour and get say ten minutes running time. I did all the usual checks for voltage and earthing. All diagnosis performed while fault on as follows:
sparks looked a bit orangy, variable and weak.
So I changed the leads which varied wildly in resistance.
sparks looked a bit orangy, variable and weak.
So I changed the plugs which looked in poor nick although the right colour.
sparks looked a bit orangy, variable and weak.
So I changed the Ignition Module.
sparks looked a bit orangy, variable and weak.
So I changed the coil.
sparks looked a bit orangy, variable and weak.
So I thought about the Hall sender and not knowing that JK do one I changed the Distributer.
sparks looked a bit orangy, variable and weak.
So I gave up on the sparks and checked the injection pulses as per the now purchased Bentley manual. Having an oscilloscope but not knowing the correct pulse width I performed the simple test light test which gave the correct- flickering bulb - result. Now having the bentley manual I checked all the other stuff like temp senders, cold start system, Airflow potentiometer (Some potentiometer!!!) etc. By this time and with a big holiday trip looming I actually considered converting to carb/s. In desperation I came onto the forum seeking a loan ECU having spent considerable amount of time and cash without getting anywhere. To say nothing of six recoveries by my now somewhat less enthusiastic ex motor mechanic friend who had by now lost all confidence in our combined and not inconsiderable diagnostic abilities. Out of the blue I was PM'd and offered an ECU to try and when was duly delivered by the "Pony Express" I set out for another tow home scenarion with the "new" ECU ready to swop. Sure enough after about 27 miles the engined died. When the ECU was replaced it ran and just to check it would not run with the old ECU. I was able to purchase the loan ECU and another which I have stashed away in the van with the parts I now have as a result of what some would decribe as my somewhat haphazard trouble shooting regime. My thanks go out to all the forum members who offered advice and particularly Beaker and Harry Man Who I feel have acted above and beyond the call of duty so to speak. Moral of story - who knows? I thought I knew a bit about motors...
Regards
Ken

2.1 Intermittent running and 'Vanagon Syndrome' is now quite well covered in the Wiki, so if you do suspect it - read the lot...
https://club8090.co.uk/wiki/Pe ... ittent_2.1

Is the idle stabiliser circuit bypassed with the two plugs connected as per set up timing procedure. Often the stab unit fails and peeps bypass it and then turn up the idle on the throttle to get it to run, then fiddle with the co setting to get it through emmissions, but as turning each screw affects the mic the correct setting takes a while with the correct gear you end up with something like yours if messed with without care.
There's a really good procedure in Bentley for checking it all out and that's the way to go. It's for the US Digijet which is 1.9 with lambda, just ignore the lambda bit otherewise it's right for the DJ.