Urgent Prins problem - dead fuel pump, no cold starts!

[camaro]

I have a 1998 Jeep Grand Cherokee 4.0, fitted with one of the older Prins systems, with the button like this - (hope that worked!)

I have previously asked if it could start straight on gas, the way my old Jeep did (King system - hold the button down and it starts on gas, runs lumpy for a couple of minutes, then is fine) and Simon was good enough to tell me that it won't do this.

Well, he was proved right - my petrol pump failed yesterday. It is a complete ball-ache to get to the pump or wiring, and the system starts fine on gas when the engine is warm - but now that it has been left overnight, I have no way to get the engine warm, because I can't start it on petrol! And no way will it start direct on gas - apparently the 2.0 system by Prins has this built in, but the earlier ones didn't.

I urgently need to use the Jeep on Monday - is there any way at all that I can hot-wire, trick, fool, or otherwise bugger about with the system so that it will think it is on a warm engine and fire up? I am happy to wait a few minutes until it comes up to temperature and runs properly - but at the minute I can't do that, as it won't start on a dead petrol pump!

Any help would be VERY much appreciated...

Cheers,

Patrick.

[Gilbertd]

When it's warm does it start on gas or does it start on petrol and switch over almost immediately as most multipoint systems do? If it starts on gas then you should be able to short out the temperature sensor which will tell the ECU that it is already hot but I suspect it starts on petrol in reality. No harm in trying it though.

[camaro]

When it's warm, it'll start straight off on gas, doesn't even touch the petrol as far as I can see - but if I leave it overnight, it has the engine cold and the gas won't even have a chance. So I am buggered as to how to start it.
The net tells me that the temp sensor is an NTC resistor which reads 2500 ohms @ 20 degrees - but also tells me that there are two temp sensors, one in the filter and one in the vaporiser -have tried shorting out, and disconnecting, the one in the vaporiser - no difference, still no start or even a pop.
The one in the filter is a 4 wire job - no idea how to try and trick it, I have tried with it disconnected and still not even a pop.
I'm thinking there must be a way to trick it, as I know systems can start straight on gas - but this Prins system has no user option like that, and I don't have a garage that I can keep it at 40 degrees overnight in!
Have tried ether down the intake boot to get it going, but there is only one of me, and I can't turn the key and spray the ether at the same time.
No luck so far, the battery is nearly dead so I have stuck it on charge, hoping somebody knows how to fool the system into thinking it has a warm engine!
I have another Jeep the same with a King system - thinking of swapping over the front end but that's a pretty big job, and I have no idea if the injectors etc. are even compatible - I'm getting desperate here, I do NEED the Jeep for Monday!

[Gilbertd]

How about an alternative approach? I suspect the petrol pump is the same as on my Range Rover and inside the tank with no access hatch in the floor so you'd need to drop the tank? How about fitting an inline pump in the fuel line after the tank so it sucks through the dead one? You could power it from and ignition switched supply or even from the fuel pump relay. I've got a pump from an older Jag where they mounted the pump in the boot that I've used to do the same thing, fitted it in place of the fuel filter as a get it going bodge. You'd need something like this http://www.fuelpumpsonline.co.uk/sytec- ... 1933-p.asp but you could probably get something from a motor factors or scrapyard. To run a fuel injection system you'd need something from another injected car as it needs to run around 35-50 psi so don't go for the 4-6psi prime pumps used on carb engined cars as an alternative to the mechanical lift pump.

[camaro]

Aye, same thing - no access hatch , so would have to drop a 90 litre gas tank, 25 litre petrol tank (both brimmed), and the towbar all at once even to access it! I'd be happy to do away with the petrol all together even if it meant using flashlube or similar - but I have no fuel pressure guage even to see if the pump is working, and can't hear it because Jeep decided to put in so many motorised gubbins that for about the first ten seconds all you can hear is various motors buzzing all over the place - also, the pressure regulator and most of the fuel controls are built into the pump assembly, and it won't start without those - so it'd be a pretty big job to run an external pump.
I'm really hoping there is a way to "trick" the gas ECU into thinking it's on a warm engine!

[LPGC]

When cold it will want to start and run on petrol for a user defined length of time, even when warm it likely does the same except the length of time may be short enough that it seems it starts on petrol.

I have fixed a few Jeeps that wouldn't run on petrol due to corroded wiring at the multiplug to the petrol pump even on standard petrol tank setups. When an aftermarket petrol tank is fitted the original fuel pump is removed from old tank and fitted to the new but the wiring might not reach to the new position - The installer may have extended fuel pump wiring and there could be corrosion where wires have been connected.

Always possible to see if the fuel pump is working - just remove the bleed cap from the fuel rail and press on the valve pin to see if fuel squirts out.
Where I have converted Jeeps with aftermarket tank I have sometimes emptied the original tank... by removing the pin valve (using a tyre valve removing tool) and Jclipping a fuel hose between the valve and another container, then forcing the fuel pump to run.
It may be possible, going along the lines of Gilbert's thinking, to reverse this process using external tank full of petrol with another fuel pump forcing fuel into the rail through the valve - only thing is the fuel pressure control valve would mean the external tank would quickly be pumped into the onboard tank, but it might get you running on gas when the engine has warmed up.

If you want to persevere with trying to start directly on gas, the gas vapour temp sensor won't make any difference. You could try varying resistance in place of the reducer temp sensor but would probably at least need software to adjust how long the engine will run on petrol for with a warm engine and (I'm not sure if this is possible) adjust other changeover conditions effecting when the engine will switch to LPG (might not switch due to high manifold pressure, low rpm, long injector pulse duration). Even then it might not start on gas due to overly rich mixture (LPG over rich due to petrol cold start enrichment strategy, cold gas from reducer, etc). Could probably get around cold start enrichment by putting yet another resistor in place of a temp sensor (engine coolant temp sensor).

Where we fit aftermarket petrol tanks on Jeeps, petrol and LPG tanks are often mounted to the same frame so are bolted to the vehicle as a job lot.. Still a lot of messing involved routing piping etc but not always as complicated as at first seems, except your job lot will be very heavy. Where I've seen petrol pumps fail on installs with aftermarket tanks, sometimes it's been because the steel tank has been stood near empty so rust has developed inside and the installer somehow made a hole in the on-pump filter screen so the pump has had rust particles go through... but as said above, most faults due to wiring.

Suppose you could always empty the petrol tank and while it's still installed fit outlets to connect an inline pump and pressure reg inline on the return... Obviously doing something about petrol vapour especially if this would involve any hot work!

You're sure it is the pump that's broken and not something else gone wrong - Are the petrol injectors still being pulsed / If the Jeep was ever fitted with single point system previously, the original install might have included a relay to shut off the petrol pump when on gas which could still be fitted / Problems with hot or cold starting can be due to faulty crank sensor (bugger to change on the 4L!).. will it attempt to run if you have it up the nozzle with ether (Easy Start)...

Might be worth a shot at varying resistance across reducer temp sensor, and then if it does switch to gas as quickly as you reckon with warm engine, you might be able to get it running on ether long enough for that to happen.

Simon

[camaro]

I presume the gas injectors run off the petrol injector pulses, so if they aren't coming through then the gas system wouldn't work at all - which it does, perfectly, once the engine is warm! And I can't get it warm, as it refuses to run on petrol.
It's basically a big old AMC tractor engine, so keeps the heat for a good while - I can leave it for an hour, and it'll still start and (seems to) run straight on gas.
But overnight - nope.
It's a Tinleytech tank setup, with a beefy skid plate under it - big gas tank, small petrol tank. I'd typically fill the petrol at the same time as the gas (confuses the girl at the till to no end!)
I can't find the wiring for the fuel pump, without dropping the whole lot out - which would need a couple of trolley jacks and risking rounding bolts, etc -
Do you think it would be possible to set the firmware to switch to gas at, say, 2 degrees? I used to be able to do this with my humpy bugger of a King system, it'd stutter and stall for a few minutes, but eventually get happy and run fine.
I have an LPG station near home, half way to work, and about half a mile from work (Flogas Belfast HQ), so could easily keep it topped up with gas all the time, and not use petrol at all - does the Prins ECU allow such a low changeover temperature? If so, I'll be straight on to you Simon, and order up the necessary kit!

Many thanks,

Patrick.

[topcat2006]

What about using a hot air dryer or similar to warm up the temperature sensors to get it started?

I had a 98 GC with the same two yak set up you describe - the fuel pump failed on that and to get to it I peeled back the boot carpet and made an inspection hatch above the fuel pump as all the frame nuts and bolts were rusty and I didn't fancy my chances of removing it.

I found on eBay a fuel pump in Cambridge area and a courier who could do same day delivery and managed to get there jeep started on the same weekend as I wa sin a similar situation to you.

Tom

[camaro]

Well, I messed about with resistors, an external fuel pump (from an old Mk2 Golf Gti) and a jerry can of petrol all yesterday - still not even a stutter!
Afraid the hairdryer (or paint stripping gun?) is out - as sometimes I'll be in the office all day, and have to park at the far end of the car park, where there is no power (about 100m away from the building!).
Topcat, do you remember whereabouts the fuel pump was on the petrol tank?
The tank runs right along the back of the jeep, so I would need to start drilling inspection holes to find it, before cutting an inspection hatch to take out the pump - is it in the centre, or to one side, do you remember?

[topcat2006]

Well, I messed about with resistors, an external fuel pump (from an old Mk2 Golf Gti) and a jerry can of petrol all yesterday - still not even a stutter!
Afraid the hairdryer (or paint stripping gun?) is out - as sometimes I'll be in the office all day, and have to park at the far end of the car park, where there is no power (about 100m away from the building!).
Topcat, do you remember whereabouts the fuel pump was on the petrol tank?
The tank runs right along the back of the jeep, so I would need to start drilling inspection holes to find it, before cutting an inspection hatch to take out the pump - is it in the centre, or to one side, do you remember?

IIRC it's in the centre of the tank. I'm pretty sure I could feel it and see the wires when I went underneath so I knew where to cut. There is a flange that holds it in place. I'm pretty sure I did not have to drop the seats either so in the boot space.

Sorry I'm not more exact - this was 4-5 years ago....

Tom

[camaro]

That's great, thanks Topcat!
I have a big skid plate on the bottom of mine so can't get near it to reach the wires or anything - so a hole in the floor it is - if it ever stops raining!
I might actually email Tinleytech who sell the whole assembly, and see if they have any drawings or diagrams giving an exact position - the closer the better!

Thanks again,
Patrick.

[camaro]

Well, Tinleytech have given me the measurement - the centre of the fuel pump hole is 420mm from the edge of the tank, measured from the filler cap side. That should make for a bit less guesswork!

[LPGC]

Aye... I've got one here!

Simon

[camaro]

Should have known you would have, but didn't want to hassle you any more than I need to!
Charlie at Tinleytech was good enough to give the measurements - though he did accidentally typo it as "4210mm from the edge of the tank" - great customer service I thought, till I realised that would mean the Jeep was about 8 metres wide.
So I asked him to clarify and he had indeed added an extra zero - 42cm from the edge of the tank, measured from the filler cap side.
Should be sorted soon, if it EVER stops raining!

[LPGC]

I need to correct my above post! I've remembered that the tank I have here is for a 3.7 Cherokee (as opposed to 4L Grand Cherokee), so would have been no good me measuring that tank. I bought it new but the customer changed their mind on choice of tank for a Cherokee, this was a few years ago so it's new but old stock now. Might have stuck it on Ebay before now if I thought there'd be any interest but it's for a very specific application - All the different Jeep models (where possible to fit a different design petrol tank) need a different spec tank, the 3.7 Cherokee tanks are different even between models that have a towbar and those that don't, the towbar spec tank will fit on models without a towbar but not vice/versa, model I have is towbar version.

Cutting out a section of floor is a good idea given the circumstances. I'm currently removing good bits from my old Grand Voyager (which was in good working order before I nicked it's petrol ECU, then it's radiator, gearbox, steering rack, handbrake mechanism...) to fit on my other Grand Voyager. Since it will now be scrapped, when it came to undoing the difficult to access LPG tank bolts (fairly new 720x270 4 hole which I want to keep) I too cut the floor out (with a large angle grinder) but I didn't have to worry about the state of the car afterwards! Should be no problem cutting the small section out the floor of your Jeep to access petrol pump though. as long as you don't have to go through any cross members..

Bet you did think, and still do think, that TinleyTech gave good customer service... the simple typo soon cleared up!

Calling you 'Nesh' regards the rain, can assure it won't hurt you! Though I'm not sure if the term is only known around these parts

Simon

[camaro]

Hehe, I have been given the measurements for a ZG tank, and now have a 5" hole saw with cordless drill from a mate who works on oil tankers - drill is about 1/4" long, so won't hit much, and the hole saw should do the rest. I hope. But if you hear about a massive fire, that's me!
And today it is sunny, but I am hungover - so tomorrow the open heart surgery will start!

[LPGC]

I usually opt for a bacon sandwich if hungover

[camaro]

I left the sandwich till later and went straight for the surgery!
So, old fuel pump is out (through the boot floor) and the new one has arrived - should get a chance to stick it in tomorrow, and hopefully my problems will be solved. I will keep you updated. At least if this new pump ever goes bad, I'll have easy access to yank it out!
The old one seemed to spin very slowly when stuck on a 12v supply and sounded like it was pumping wet sand, so I'm hoping that was a bad sign for it, and I don't have to dive into nightmare Jeep electronics...

[camaro]

Well, the new pump is in (5 minute job - shove pump into hole in tank, snap fuel line on, snap fuel connector together, turn key - start! Warm up in a few seconds, switches to gas, runs just like it used to.
I think it's about time I set about creating a hangover for tomorrow...

So if anyone wants a pic of where to cut to access the fuel pump, I have one...

Thanks to everyone for your help, particularly Simon! If I ever have the Jeep over in Yorkshire, I shall be sure to call and book a tune-up!

[Morat]

Hmm, I think the hole in my tank is a bit small - it takes me ages to line up the rubber seal thing properly. Maybe the fact that the access hole in my boot floor is off centre makes more of a difference than I thought.