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PostPosted: Mon Oct 10, 2016 12:24 pm 
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Or maybe that's the wrong term... 1998 Grand Cherokee 4.0l, Prins LPG system fitted. Runs perfectly (and very economically!)
Problem is, when I run on petrol everything is fine. Switch to gas, and I get a check engine light.
The code reader complains that the petrol injectors are misfiring, I assume because they don't fire when the Jeep is running on LPG!
Should I plug something in, to "trick" the ECU into thinking the injectors are working fine, all the time?

Cheers,

Patrick.


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PostPosted: Mon Oct 10, 2016 12:46 pm 
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Yup, assuming it's a single point system, you need one of these http://tinleytech.co.uk/shop/lpg-parts/ ... r-engines/

If you've got a multipoint (doubtful on an older Jeep), then it will be dealt with in the controller.

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PostPosted: Mon Oct 10, 2016 1:56 pm 
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It's a multipoint system, so either it doesn't deal with it in the controller, or it's wired wrong! Was only converted a few years ago, maybe 7?


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PostPosted: Mon Oct 10, 2016 4:12 pm 
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What system is it? As a multipoint will intercept the pulses to the petrol injectors the ECU shouldn't notice anything different.

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'96 Saab 900XS, AEB Leo, sold
'93 Range Rover 4.2 LSE, Lovato LovEco, sold
'98 Ex-Police Range Rover 4.0, Singlepoint AEB Leo, my daily motor
'97 Range Rover 4.0SE, eGas multipoint, a project.....

Proud to be a member of the YCHJCYA2PDTHFH club.


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PostPosted: Mon Oct 10, 2016 4:29 pm 
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A Prins VSI system, I can't find the fitting certificate for it, but it cost £2000 when it was fitted - and has 6 separate injectors. It doesn't really bother me, but if I can plug in something cheap to keep the check engine light off, I'll do so!
I have the official software for it, and an interface lead, but haven't yet had a chance to plug that in and have a good look at things - maybe it's a setting in there somewhere?


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PostPosted: Mon Oct 10, 2016 6:33 pm 
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I held back from posting because I suspected it might have been a VSI system.

Your saying 'misfiring petrol injector' leads us to assume the OBD code is actually something like 'disconnected petrol injector / no petrol injector'. Info in the rest of this post is only relevant if that assumption is correct. 'Misfire' on a cylinder without mention of injector(s) would more likely just point to a misfire, in which case info in this post will not be relevant.

If assumption is correct your problem will either be a broken Prins emulator/injector switching module (2 of these on your install), or further injector emulation is needed.

Further injector emulation can be necessary where the petrol ECU is fussy about the resistance across petrol injectors that it reads, effectively interpreting injector resistance above X ohms as broken or disconnected petrol injector, and Jeeps can be fussy.

On an AEB system such extra emulation is easily achieved by simply unplugging the injector harness connections (2 on a vehicle with more than 4 cylinders) and plugging an AEB124 unit in the middle (so 2 would be needed on your 6 cyl Jeep), on a none AEB system (like your Prins) you could still use AEB124's but would need to hard wire them in.

AEB124's pretty much just place 50 ohms of resistance across each injector wire cut, so when running on LPG the petrol ECU sees the resistance of emulation provided by the LPG ECU in parallel with the 50ohms of the AEB124 (and when running on LPG the AEB124 is itself in series with the petrol injector's resistance, normally 13 to 16ohms). You can gather from this how hard wiring in such as AEB124's should be done.

It is possible to use a Pitagora type emulator like the one Gilbert linked to instead of the AEB124 type, but doing so means that as soon as the LPG solenoids are turned on, which can be some time before the LPG system switches cylinders to run on LPG, the petrol ECU sees the petrol injector resistance in parallel with the Pitagora's resistance, so the petrol ECU's injector outputs can be under more electrical load than they would usually be when running on either petrol or LPG (particularly more than when running on LPG because emulation resistance is usually nowhere near as long as petrol injector resistance).

Easy enough to come up with a home made AEB124 but first worth checking those Prins units. Does the error only crop up for one cylinder or more than one?

Edit 11/10 Actually since VSI injector emulation/switching units are remote (of ECU) it would be possible to use Pitagora wired to turn on when the emulation/switching unit does, quite simple to do. But if the error only occurs on one cylinder then it is likely a Prins injector unit has failed on the effected channel. If a Prins injector unit has failed you might as well replace it as buy a Pitagora as there won't be a vast difference in price.

Or to effect a much cheaper but slightly involved and less tidy repair it would be possible to make up your own single cylinder emulator that switches on at the same time as the Prins emulation - Get a little relay, connect it's coil across red and brown wires (switching wires) on failing Prins injector unit, connect one side of relay switch to effected cylinder's petrol injector petrol ECU side wiring (will be one of the striped wires to the Prins emulator - tell us which cylinder and we can tell you which wire), connect other side of relay switch to one side of a pack of resistors you made up (I'm coming to resistor pack), connect other side of resistor pack to Prins ECU's ignition on wire (or battery positive, via a fuse in either case). Resistor pack: Petrol injectors are 16ohms, if we aim our emulation resistance somewhere between this nominal injector resistance and the resistance provided by emulation built into most LPG ECU's it should work well, so somewhere around 40ohms should work well. 40 Ohms at 12v will flow 0.3 amps and 0.3 amps at 12v would be 4 watts. Little resistors are only a quarter watt, so if we use little resistors (wired in any combination of serial or parallel just so long as each resistor flows equal power) then in order not to burn them out we need to use at least 16 of them and not pack them tightly together. So then for example, to err on the safe side we could use 16 x 47ohm resistors wired as 4 sets of 4 resistors wired in parallel, wired in series. This would give 47ohms of emulation, which is closer to the 50ohms that most LPG ECU's use for emulation and means resistors won't be pushed as hard. A little relay would cost pennies and a strip of 47ohm resistors would cost pennies, but then you've got to make it all safe and tidy!

Simon

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Last edited by LPGC on Tue Oct 11, 2016 11:51 am, edited 1 time in total.

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PostPosted: Tue Oct 11, 2016 11:42 am 
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Ah, something to look for! The fault comes up on all 6 cylinders, so I suspect an emulator or home-made job is needed - I might try that at the weekend. Or I might just leave the "check engine" light on and not worry about it!

Thanks all,

Patrick.


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PostPosted: Tue Oct 11, 2016 11:53 am 
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Tell us again what the code says (exactly), and just to be sure - what's the code number (P????) ?

There are potential issues (besides the check light) with OBD errors such as disconnected petrol injector.. Might not be relevant on a 98 Jeep but on post 2000 Jeeps the engine would probably run in limp home mode with such errors logged, so runs open loop instead of closed loop - economy and drive-ability suffer a bit, but if open loop means a lean mixture could also damage valves. On post 2000 Jeeps the cruise control also stops working. Is it running closed loop with the check light on? If open loop, what is lambda under various driving conditions?

As I said above, Prins VSI1 injector emulator/switching units have 4 channels, so on your Jeep there will be 2. If the OBD error does point to disconnected injectors and if errors were only on one cylinder or half of the engine's cylinders then we might expect one of these units to be duff but it is less likely that both units would be duff... So with this error reported for all cylinders it would seem you'd ideally need 2 x AEB124's, but could probably get away with 1 x 6cyl Pitagora particularly if the error isn't reported immediately. Would still go with 124's as they're designed for this purpose and total cost would only be about the same as with Pitagora. If Pitagora is used you wouldn't use as many wires, only connecting 8 (including 2 switch wires) as opposed to 124's 12 (no switch wires needed). Couple of potential problems using Pitagora include switching speed (but likely OK as would think quick enough) and switching voltage - Pitagora is switched via 12v while I'm not sure if Prins switching units are switched with 12v or 5v (but I believe 12v, in which case not a problem - but even if were a problem could use a little 5v coiled relay to forward 12v to Pitagora).

Couldn't simply use a Pitagora in place of the Prins units because Prins units have petrol injector inputs, petrol injector outputs and petrol injector signal wires branch out of them to run to the VSI ECU, Pitagoras are missing the VSI ECU branching... May be possible to adapt Prins wiring to work with Pitagora(s) instead of Prins units but would be more work, not save much cash, and if only a few of us on this forum ever stopped using it and you had a problem in future, most Prins installers wouldn't know where to start if you had to take the vehicle to them for diagnostics :lol:

Simon

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PostPosted: Fri Oct 14, 2016 4:04 pm 
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Well, I finally got round to scanning it again - I have a P204, 205, P206 - injector misfire on cylinder 4, 5, 6 respectively. I must have misremembered - it was probably my previous jeep that threw up fault codes on all six!
So I am assuming there are two Prins emulators fitted, each handling 3 cylinders, and one has gone bad/become "unwired".
Cruise control is fine and dandy, though the Jeep seems a little down on power - but it is due for new ignition bits (plugs, leads, dizzy cap, rotor arm) which won't help either - I have the parts, but finding time to fit them is a problem.
Are the Prins emulator units expensive, and just a "plug in" to the harness? And where might I find one?
If they aren't expensive I might as well get a new one so the Jeep is "just right"...

Cheers Simon, you are a mine of information!

Patrick.


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PostPosted: Fri Oct 14, 2016 5:41 pm 
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Your codes do point to 'injector circuit malfunction' on 4 5 and 6 - best to use correct terminology 'injector circuit' because any mention of 'misfires' could lead to incorrect interpretation of your fault.

There could be 2 x 4 cylinder emulators fitted but, come to think of it, Prins do make a 6 cylinder emulator and 1 x 6 cylinder emulator might be more likely to be fitted than 2 x 4 cylinder emulators on your 6 cylinder application. They make 6/8 cyl specific looms but an 8 cyl loom could be used on a 6, more expense for installer's bits but if they had one on the shelf... and were confident enough to use it (probably not).

Here are links to 4 and 6 cylinder units sold by Tinley Tech, £41+VAT or £61+VAT respectively.
http://tinleytech.co.uk/shop/lpg-parts/prins-injection-module-for-4-cylinder/
http://tinleytech.co.uk/shop/lpg-parts/prins-injection-module-for-6-cylinder/

They are just plug in, nothing to configure. Note the 'allow 10 days for delivery' bit in the links - actually usually in stock but if not 10 days as written.. some of us keep them on the shelf because they're a common Prins failure part. Now you know what you're looking at (pics in links on TinleyTech's site) you'll easily find if you have 2 x 4 units or 1 x 6 unit.

If you have 2 x 4 cyl units you could test yours by swapping them over - if fault moves to 1 2 3 it may confirm the one originally serving 4 5 6 is at fault. I say may instead of will, because Prins convention is for one unit to run odd cylinder numbers, the other unit to run even cylinder numbers and since your engine has a straight 6 engine cylinder numbering is simple 123456, so following Prins convention would expect a duff emulator to cause codes for either odd or even cylinder numbers. I might add that Prins installers tend to follow wiring conventions/instructions to the letter, for better or for worse, but maybe because they wouldn't know the outcomes of deviation from instructions. Installers like myself are less likely to follow instructions but would know how that would affect the outcomes for worse or for better. Prins lists only a single wiring diagram for a certain number of cylinders even for V engines, while V engine manufacturer's cyl numbering might have (V8 example) 1234 on one bank and 5678 on the other bank, or might have 1357 on one bank and 2468 on the other..

As said, more likely you have a single 6 cylinder unit - in which case this could have an internal fault causing the problem on cylinders 4 5 6. The easiest way to confirm/disprove this would be to swap in another 6 cylinder unit, which in your case would mean buying a new one because you won't have 2 x 6 cyl units.

It is unlikely but possible that the Jeep's OBD is seeing and reporting the fault on 4 5 6 but not 1 2 3 even though the same fault/condition exists on 1 2 3 (Jeep OBD might report 1 2 3 fault given enough time or if the fault on 4 5 6 is corrected - OBD cannot always be totally trusted to report all faults in cases of multiple faults). This situation could lead to misdiagnosis (of unit failure) in case of 1 x 6 unit, in which case the real fix would be extra emulation on all cylinders. But if you have 2x4 units and swapping them moves the code from 4 5 6 to 1 2 3 then it's safe to say the problem is a failed 4 cyl unit.

Simon

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PostPosted: Wed Nov 02, 2016 10:40 am 
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Well, I have finally got round to having a look, and found 2 emulators tucked away in a suitably inaccessible place - I'll have to take half the engine ancillaries off to get them out, by the looks of things!
Then I'll swap them round and scan for codes to see which emulator is faulty, and pick up a new one - one of these days... (I am NOT a fast worker! :lol: ).

Thanks to all yet again, particularly Simon - could you upload your brain onto the internet or something, so we don't have to bother you? :mrgreen:

Cheers,

Patrick.


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PostPosted: Wed Nov 02, 2016 11:11 am 
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camaro wrote:
Well, I have finally got round to having a look, and found 2 emulators tucked away in a suitably inaccessible place - I'll have to take half the engine ancillaries off to get them out, by the looks of things!
Then I'll swap them round and scan for codes to see which emulator is faulty, and pick up a new one - one of these days... (I am NOT a fast worker! :lol: ).
Actually on the engine itself (you said have to remove engine ancillaries?) would be a bad and a strange place to mount them. No problem with them being in the engine bay, shouldn't be on the engine itself though.

camaro wrote:
Thanks to all yet again, particularly Simon - could you upload your brain onto the internet or something, so we don't have to bother you? :mrgreen:
Cheers,
Patrick.
With the length of some of my posts, some people might believe I am attempting to do just that... But unless we all really live in 'The Matrix' the closest thing I'll get to Matrix will be Matrix injectors. Hang on, I never noticed this USB socket sticking out of back of my neck before... :roll:

Simon

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PostPosted: Wed Nov 02, 2016 11:53 am 
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Hehe, well they aren't on the engine or any of it's ancillaries - just tucked under the gas ECU bracket so I'll have to remove that first, and to remove that I'll have to shift the alternator, and then find a wobbly ratchet spanner to undo the bracket. Not a huge hassle, they could just have made it a lot easier!


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PostPosted: Wed Nov 02, 2016 6:33 pm 
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Fitted those parts there on this model of vehicle... :roll:

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