Hesitating 1991 BX19 TZI - Canister purge electrovalve?

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TZI
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Hesitating 1991 BX19 TZI - Canister purge electrovalve?

Post by TZI » Mon Apr 28, 2014 9:06 pm

Last week, 10 miles from home, my TZI started to stutter. Losing power and then picking up again. The diagnostic light was coming on or going out just before each hesitation (i.e. if it went out a hesitation followed and if it came on the same thing). There were odd periods of running fine then hesitating again. The car never cut out completely and I was able to make reasonable progress home. This does not feel like a misfire on one (or even two) cylinder(s).
On tick over, about every 3 seconds or so, the revs drop and then pick up again and the diagnostic light flashes on. This is consistent.
I initially suspected the throttle position sensor and as I had a spare I quickly swapped that but no change.
With some diagnostic equipment (a length of wire and an earth point) I retrieved three error codes from the ECU:
15, fuel pump relay feed
34, canister purge electrovalve
42. injector
I swapped the fuel pump relay but no change so the next job (scheduled for Wednesday evening) is to remove and clean the canister purge electrovalve and perhaps test it's solenoid.
Anyone with any experience of the above job or any other ideas?
Many thanks in advance.

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Re: Hesitating 1991 BX19 TZI - Canister purge electrovalve?

Post by TZI » Thu May 08, 2014 9:16 pm

I have not had much chance to look at this problem (car is in the garage whilst I cycle and motorcycle) but it appears from the Haynes manual that whilst the car has a 'fuel vapour recirculation system' this does not appear to include a 'canister purge valve'. At first glance what I thought was one of these turns out to be the 'supplementary air device' (SAD) that links pipes either side of the throttle assembly. I am not sure if this is working ok or not but at the moment I assume that it is.
I don't think that the symptoms below would be caused by a faulty SAD but does anyone know how to test it? Apparently it has a bimetallic strip that warms up and opens the valve causing the engine to run richer when cold. I have run wires to the connectors for a minute or two whilst looking through it (it is partially open) but nothing changes.
I have another fuel pump so when time allows I might change this - although the car did get a new fuel pump (not OEM) and a new fuel filter a couple of years ago. Should the fuel pressure regulator also be under suspicion?
Any ideas welcome! Many thanks.

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Re: Hesitating 1991 BX19 TZI - Canister purge electrovalve?

Post by Tim Leech » Fri May 09, 2014 1:01 pm

The canister is inside the drivers inner wing behind the liner.
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1991 BX 19TZI Auto A/C
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Re: Hesitating 1991 BX19 TZI - Canister purge electrovalve?

Post by rutter123 » Sat May 10, 2014 3:30 pm

TZI wrote:I have not had much chance to look at this problem (car is in the garage whilst I cycle and motorcycle) but it appears from the Haynes manual that whilst the car has a 'fuel vapour recirculation system' this does not appear to include a 'canister purge valve'. At first glance what I thought was one of these turns out to be the 'supplementary air device' (SAD) that links pipes either side of the throttle assembly. I am not sure if this is working ok or not but at the moment I assume that it is.
I don't think that the symptoms below would be caused by a faulty SAD but does anyone know how to test it? Apparently it has a bimetallic strip that warms up and opens the valve causing the engine to run richer when cold. I have run wires to the connectors for a minute or two whilst looking through it (it is partially open) but nothing changes.
I have another fuel pump so when time allows I might change this - although the car did get a new fuel pump (not OEM) and a new fuel filter a couple of years ago. Should the fuel pressure regulator also be under suspicion?
Any ideas welcome! Many thanks.
You can bypass the SAD by blocking the pipes up on the device , best to remove them both from the actual SAD and block them both up with a cork or


similar, this will eliminate the air bypassing it, the SAD should be fully closed once warmed up cutting off any unmetered air entering the inlet manifold, these are qjuite troublesome as over time the bimetal strip is no longer closing the little bypass window, causing idling/lean mixture/stalling/hesitation problems, i have and still am suffering same probs with my gti 8v. These are no longer available unless you are lucky to find another one from a pug 205 gti 1.6/1.9 which use the same bosch unit.
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Re: Hesitating 1991 BX19 TZI - Canister purge electrovalve?

Post by TZI » Mon May 12, 2014 11:34 am

Thanks both.
I blocked off the SAD pipes and (as I suspected would be the case) there was no change in symptoms. Before I change the fuel pump I will get to the canister and track the pipes to see if there is a solenoid operated valve anywhere. If I find it then I have one off a C5 that hopefully I can substitute. I would like to get rid of that error code before I start changing anything else.

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Re: Hesitating 1991 BX19 TZI - Canister purge electrovalve?

Post by rutter123 » Mon May 12, 2014 4:21 pm

Your running probs seems very similar to mine, starts ok idles a little high till warmed idle settles to 900rpm but when pulling away very lumpy with hesitation up to 2500rpm then a misfire/lack of fuel?? Up to 2800rpm then after that its fine and pulls well and evenly, then idle starts to rise to 1200rpm and hunts between that and 900rpm with a little cough now and again, never stalls and you can feel the engine rocking as it kangaroos down the road if you catch it wrong, it has to be driven very delicately in traffic, also gets sudden jolts on the overrun, so far i changed the coil,leads,plugs diz cap and arm, fuel pipes, filter and pump, pressure regulator, injectors cleaned, throttle body cleaned, temp sensor ok, throttle pos sensor ok, timing is set 5 deg b4 tdc, for now the SAD is bypassed as its knackered, driven on barely any throttle its fine but as soon as you try to accelerate gradually it coughs splutters hesitates misfires? Up until your above 2800rpm then it smooths out, if you boot it its barely there, for now ive got used to driving it this way but there still is a significant problem somewhere but where ECU? Have also replaced all the breathers and have no air leaks, on removal of the plugs it seems from left to right no1 is very lean no2 is ok no3 is also very lean no 4 is ok, too much air or not enough fuel? Or both? Why? How? I dont know, help?
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Re: Hesitating 1991 BX19 TZI - Canister purge electrovalve?

Post by TZI » Mon May 12, 2014 9:22 pm

Right - I have fixed it! Thanks for your help guys....

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Re: Hesitating 1991 BX19 TZI - Canister purge electrovalve?

Post by TZI » Mon May 12, 2014 9:25 pm

I Jest! It really annoys me when you get to the end of a thread that looks promising but it just peters out.
The car is now sorted (I wasn't jesting about that) but no time now to post a full reply but I promise that I will do tomorrow.

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Re: Hesitating 1991 BX19 TZI - Canister purge electrovalve?

Post by TZI » Tue May 13, 2014 9:26 am

Using Tim’s info on the location of the charcoal canister I found a pipe coming from under the wheel arch that went to the inlet manifold and sure enough on this, between oil filter and engine, was the small canister purge valve. It has one pipe in and a smaller pipe out on the other side (so it can only be fitted one way) and an electrical connector. I took the valve off and was able to blow through it indicating that it had failed.
At this point I was still not convinced that a failure of this unit would give the symptoms described above but at least replacing it would eliminate it from enquiries.

My replacement valve (from a C5) appeared identical but when I came to fit it I found that the electrical connector was facing the opposite way to the original valve and the wires from the car were too short to reach. These wires follow the pipe into the wheel arch between the LHM tank and the strut so I cut these through near the LHM tank in order to splice in a length of twin core flex.
When stripping the insulation off the end of one wire a 6 inch length of wire came away in my hand. On inspection I could see where it must have been rubbing against the car. It was worn almost right though and had obviously been shorting out. I replaced a long length of wire and put on the connector (after shaving off an extra lug on the C5 unit that prevented the connector fitting). I started up the car and the diagnostic light went out. I took it for a drive and no problems.

I was lucky!
If the connector on the C5 valve had not been on the opposite side I would not have found the bare wire. I can only assume that the revs dipping every 3 seconds (which steered me away from thinking it was a short) was due to something loading the engine every 3 seconds (alternator? Hydraulic pump? ECU input?) and this caused movement on the engine mounts causing the wire to rub. The seemingly random hesitations when driving only occurred when the right engine load coincided with the valve being activated (and the wire being live).

Many thanks again for the help.

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Re: Hesitating 1991 BX19 TZI - Canister purge electrovalve?

Post by TZI » Tue May 13, 2014 10:01 am

There was a prequel to the above that clouded my thinking a bit:
From about two years ago until a year ago I had an issue where very occasionally (once in 2,000 miles and usually on the motorway) the car would hesitate for a split second and then pick up again. No other problems. I noticed that each time this happened the tacho needle dropped rapidly and then the ignition lights came on briefly (all very quickly). All battery connectors and earth points seemed tight. This got a bit worse and then a couple of times the car cut out completely (luckily on quiet roads at low speed). As I had a spare fuel pump I swapped this but to no avail. Then a few times the car struggled to start. Battery and starter motor were changed but no joy. Eventually I had a situation where the car would turn over slowly and only fire the instant I came off the starter. This felt like a bad earth - the starter current swamping a poor earth and the ignition system only getting a look-in when the starter current abated. I revisited all the earth points. The gearbox earth point was tight but I just about managed to shift it an eight of a turn. Suddenly all was ok. I managed to get the bolt off and cleaned up the surfaces with emery cloth. Greased and replaced it and (until the more recent problems) everything has been ok since. Although the bolt was tight and a multi-meter showed no impedance it must have been corroded.
When the recent problems started I suspected this problem again but the recent hesitations, whilst feeling identical, were not accompanied by the drop of the tacho needle but were accompanied by the orange diagnostic light.
Last edited by TZI on Tue May 13, 2014 5:35 pm, edited 1 time in total.

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Re: Hesitating 1991 BX19 TZI - Canister purge electrovalve?

Post by TZI » Tue May 13, 2014 10:02 am

P.S. I have put the SAD back on and at the moment the car seems to tick over a bit fast when warmed up - 1100rpm. Now that the other issue is solved I may block it off and see what difference it makes

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Re: Hesitating 1991 BX19 TZI - Canister purge electrovalve?

Post by rutter123 » Tue May 13, 2014 3:32 pm

Dont think my gti has a purge valve.
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Re: Hesitating 1991 BX19 TZI - Canister purge electrovalve?

Post by TZI » Tue May 13, 2014 5:59 pm

Dont think my gti has a purge valve.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>

If it is a pre catalytic converter model then possibly not (my non cat, 1989, 8 valve GTi didn't have the diagnostic facility described above so you may not have that either).

The cusp of my problem was not the failed canister purge valve itself but a worn through wire caused by the engine moving on it's engine mounts under load and overrun.
This wire was from the ECU and obviously affected the latters function whenever it shorted. I can imagine that a shorted wire to any of the ECU sensors or related components might have a similar effect.
If you have not already done so I would check the wiring to all the ECU sensors/components especially between the engine and the body where they pass near anything that they could come into contact with when the engine moves on its mountings. The fact that you say that driving gently helps your issue lends a little weight to this possibility.
The sensor wires to the purge valve were quite thin and only shielded with what looked like one layer of insulation tape. They probably did well to last 23 years.

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Re: Hesitating 1991 BX19 TZI - Canister purge electrovalve?

Post by rutter123 » Tue May 13, 2014 7:30 pm

I have done this by completely unwrapping the loom and checking for any breaks, bare wires etc and its all ok, i have re-soldered the suspected dry joints on the injector part of the harness to no avail. The prob lies elsewhere as its in the same place all the time and behaves accordingly, im leaning towards fuel supply issues as plugs are still indicating very lean, poss a faulty new fuel pump?
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Re: Hesitating 1991 BX19 TZI - Canister purge electrovalve?

Post by rutter123 » Tue May 13, 2014 7:31 pm

I have done this by completely unwrapping the loom and checking for any breaks, bare wires etc and its all ok, i have re-soldered the suspected dry joints on the injector part of the harness to no avail. The prob lies elsewhere as its in the same place all the time and behaves accordingly, im leaning towards fuel supply issues as plugs are still indicating very lean, poss a faulty new fuel pump?
90 BX Tzd turbo 294k SORN undergoing major surgery
90 BX Tzd turbo estate 46k awaiting surgery
65 Peugeot Boxer Van the new workhorse
52 Toyota Rav4 180k Bulletproof Jap reliability