Over revving DJ....? Failed MoT on emissions.

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Over revving DJ....? Failed MoT on emissions.

Postby spanishfly » 18 May 2019, 17:32

I haven't found another thread about the same issue so hoping the hive mind can help....? 1989 syncro 2.1 caught in a cycle of over revving with accompanying buzzer of doom.

Van is new to me but was an opportunity too good to miss, aren't they all.. Sadly as the PO passed away I am unable to illicit further info/history from him. 78,000 miles dry stored 15 years brought out of retirement 4 years ago Mot'd and run weekly though only 2000 miles a year.

Van arrived without water due to leaking plastic pipe (now replaced with S/S), P/O had fitted shiny new heads + radiator so work has been done there. Came with a Haynes manual pages referring to ISV and TPS ringed in pen and a spare ISV.

In an effort to continue where he left off I have cleaned and tested the ISV's both seem fine are free and click.

Following the rotor arm fiasco have replaced cap and leads too so now starts on the button but.... almost immediately revs to 2200 stays there for some minutes as it warms up then revs drop for 10secs or so before returning to 2200 for 30secs back down 10s in a cycle. Ran like this for 25mins during MoT probably would do until it runs out of fuel. If started without ISV connected, or hose held shut idle returns to normal but still too rich.

Not sure whether it always has as I've had the clocks out but once warm the Buzzer of doom now comes on when in the high revving part of the cycle along with the flashing oil can scaring the daylights out of me. It does go out in the low revving part and failed the emissions with 4.44% CO2. The plug has been removed from the AFM and the ISV was disconnected so possibly some adjustment to the idle screw had been attempted too.

So far I've worked through some of the Bentley tests and ascertained that the ISV seems to work, the ISCU also and that the ECU behaves the same as my spare. The TPS is on at idle and max revs but not inbetween. Bypassing the little white box to set timing didn't seem to affect anything haven't looked at the AFM yet.

Intend to revisit timing as I only disconnected 1 of the 2 vac hoses...

Any ideas please?
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Re: Over revving DJ....? Failed MoT on emissions.

Postby silverbullet » 18 May 2019, 18:21

Check the distributor for failed diaphragm i.e. an air leak (although this should make for difficult starting, lean mixture and low CO) but often overlooked so worth checking anyway.
T1 sensor could have failed (its integrated into the AFM) which would make it run rich and "hunt" or you may have a high resistance connection in a plug (AFM, temp senders, earth returns) or a broken wire in the engine loom.
Fuel regulator could be on the way out, allowing excess fuel pressure to the injectors.
Check all the vacuum hoses.

I'd put my money on the ecu being told by the temp senders that it needs to be in cold start mode i.e. its badly overfuelling.

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Re: Over revving DJ....? Failed MoT on emissions.

Postby spanishfly » 18 May 2019, 18:55

Thanks for the advice. I forgot to mention I've replaced all vacuum hoses and checked for leaks. Also fitted new temp senders as I had spares. Remade all the earths in the engine bay and checked under dash crowns. Fuel pump is new from PO.
Not sure the definition of hunting but thought it was a more of an ebb and flow wavy kind of idle? This feels like a very specific electronically switched/controlled cycle over a much longer time period. I haven't attempted to time it accurately to check but will do on Monday.

The high pressure circuit buzzer is really annoying as it introduces a sense of panic! It does seem like it's continuously overfueling though like it thinks it's freezing cold.

Could the high pressure sensor be confusing the ECU?

I guess I really need a gas analyser to try and return the AFM and mixture back to factory settings.. if they've been changed.

I think ages ago Aiden or you said something about not assuming a new part is good. Maybe the T2 is bad... I'll read about checking them both anyway.
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Re: Over revving DJ....? Failed MoT on emissions.

Postby Aidan » 18 May 2019, 23:08

Is this the blue Caravelle that was sold on Ebay by Dazzer in Manchester ?

At idle the switch under the throttle body should switch and tell the idle control unit 'you have charge' and the idle control unit behind the right rear lights runs the engine; it controls the air bypass valve and the fuelling to ensure the engine runs at 850rpm ish
It gets signals from the usual suspects and the power steering pump which tells it if demand is coming from the p/s and so it increases revs, also from air con compressor for same reason - if it doesn't have either check that stray wiring isn't affected by being grounded, the conenctors are usually cable tied if not in use
I'd remove the idle control unit and clean up the contacts in the relay plate that holds it and clean all the terminals on the idle control unit, it can get damp in the bottom of the pillar so corrosion can be an issue; the units themselves get flakey too, they are old school components on a circuit board folded in two, capacitors especially fail
BOD circuit is discreet from engine management, housed in dash, and is switched at 2000 rpm to then look for high pressure sender to be earthed, so again poor contact or wiring fault, either at 14 pin multiplug or at sender is likely cause of it going off, it just happens to be an issue at this time by coincidence, but because the revs are exceeding 2k it is coming on 'at idle'
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Re: Over revving DJ....? Failed MoT on emissions.

Postby spanishfly » 19 May 2019, 08:20

Thanks for the patience Aidan, no not the one from Manchester the one from Essex from a few weeks before on FB.

That makes sense. I think I now have a handle on what should work but am foggy on the interpretation of the facts!

To recap.

The ICV plunger can easily be moved with a screw driver in the hole, it clicks, snaps on an external battery and may buzz a little though not very noticeably.
With ICV connected idle is 2000 rpm.
If the air flow is restricted revs fall to 800 rpm
If the ICV is unplugged revs fall back to 800 rpm.

Am I correct to interpret this as ICV is working but the info from the control unit is wrong?

Somewhere I had found reference to the ISCU stating that voltage between 7? and 14 should be 'battery', but I'm only measuring 10.3V so not battery and between 5 and 8 should be 5V which it is when running which I think confirms that the TPS is functioning but that the ISCU isn't.

Samba mentions a transistor that fails in these boxes..... perhaps the 10.3v reading is enough of a shortfall to cause the box to be overfuelling?

Anyway seems like I need a new or known good s/h ISCU before I can properly check the mixture screw and AFM screw.

Meanwhile I'll try and find why the BODS circuit is active. Did have a brake fluid spill in the dash whilst bleeding so will look there before diving back in to the engine compartment.
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Re: Over revving DJ....? Failed MoT on emissions.

Postby Aidan » 19 May 2019, 08:49

sounds like maybe the air by pass valve is sticking open, or it's being forced open by the iscu because it's getting bad info, bad contacts, or is faulty
don't pry the valve, clean it with carb cleaner, cheap stuff is fine just take it off and fill it up let it evaporate and repeat, try putting some in both apertures, they gum up because of oil vapour from crankcase breather
I don't have a spare DJ iscu here unfortunately, I run MV engine and the units are different
251 907 393 suffix A or C are for DJ, suffix B and D for MV
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Re: Over revving DJ....? Failed MoT on emissions.

Postby ajsimmo » 19 May 2019, 09:52

I have these.
https://rover.ebay.com/rover/0/0/0?mpre ... 3560080222

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Re: Over revving DJ....? Failed MoT on emissions.

Postby spanishfly » 20 May 2019, 17:48

Just to put this conundrum to bed and thank everyone for their help, today whilst removing the ISCU to get the number I pulled extra hard on the cable which came through the rear light hole revealing the bundle of cables gnawed by rodents to the point that 4 wires were severed and 3 hanging by a few strands and doubtless touching It's amazing it ran at all and I thinks perfectly explains the low voltage and intermittent errors.
Have now reset the timing and needed to screw the mixture in almost all the way to attain the correct idle. I suspect the PO had no idea about the rodent attack and had been attempting to reset the timing , mixture and AFM screws to make the van run with the ISV disconnected.
As I don't have access to an analyser am keeping my fingers crossed it is close enough to stock to pass the MoT....... until I can find someone to help reset the AFM if necessary?
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Re: Over revving DJ....? Failed MoT on emissions.

Postby silverbullet » 20 May 2019, 18:39

Well that explains a lot! Glad that you found an obvious fault.

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Re: Over revving DJ....? Failed MoT on emissions.

Postby spanishfly » 06 Jun 2019, 17:20

Just in case my over fueling helps anyone else. I investigated the injector that was reading low impedence 11 ohms rather than 17 ohms like the others and close to Bentleys 16-16.4, replaced it with a rebuilt one and now they all matche! 17 ohms all round.

Next step is to find an analyser and see if the emissions have dropped. Certainly sounds smoother though I still suspect AFM settings are a bit out.
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1987 Dehler Profi 2+2
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