Cutting out when on gas

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HMJonesy
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Cutting out when on gas

#1 Post by HMJonesy » Tue Nov 05, 2019 12:20 pm

Yesterday morning I drove to work absolutely fine. Jeep flicked over to gas as normal and drove fine as it always has.

After arriving at work and while parking the jeep it cut out. Now when ever its on gas the revs drop and cuts out but runs perfectly fine on petrol.

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Re: Cutting out when on gas

#2 Post by LPGC » Tue Nov 05, 2019 12:22 pm

I've edited this post a few times now lol...

WJ Jeep (from your other thread). What year, what engine and what LPG components? Is it changing to LPG at the normal changeover temp still? Is the engine warning light on?

How come you posted on the other thread saying all was well only 4 minutes before mentioning the new problems on this thread?

Aha must be this...
OnTheFenceDev wrote:
Tue Nov 05, 2019 12:00 pm
Testing timestamp - apparently there is an issue now that we are back in UTC (clocks went back)
Posted at midday 05/11/2019
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HMJonesy
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Re: Cutting out when on gas

#3 Post by HMJonesy » Tue Nov 05, 2019 3:06 pm

Its a 1999 Jeep grand cherokee (WJ) 4.7 V8 and it has a Stag 300-8 kit. No engine lights and switches over to LPG at the temp it always has done before.

Jeep runs flawlessly on petrol but when it changes over to LPG it will run until I start to drive and then when I come to a stop the revs drop and the engine cuts out. It will start back up and switch straight back to LPG but then keeps cutting out unless I manually switch it back onto petrol.

As for the new post, its just a moment of madness on my part. I forgot I mentioned the revs dropping in that post and only got an answer for the temp issue which is what I responded to.

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Re: Cutting out when on gas

#4 Post by LPGC » Wed Nov 06, 2019 8:01 pm

Has it always done the same (cutting out) or is this a new problem? Problem could be any of many things (possibly different set of things depending on old/new problem). Is the engine warning light on?
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Re: Cutting out when on gas

#5 Post by HMJonesy » Wed Nov 06, 2019 10:20 pm

This is a new problem. I've owned the Jeep since may and this is the first time it's had this problem.

No engine light or warning lights on dash and runs perfect on petrol.

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Re: Cutting out when on gas

#6 Post by HMJonesy » Sat Nov 09, 2019 3:11 pm

Just an update, possibly fixed.

Changed spark plugs today and what a bastard that was. Don't think they have ever been changed. Coils had to be pryed off resulting in 1 broken. But now seems to be running fine on lpg.

Old plugs had next to no electrode left on them but now I have a new problem.

Got a slight miss fire when running on LPG and can hear a ticking from 1 of the injectors. Is it worth trying a repair kit?

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Re: Cutting out when on gas

#7 Post by Brian_H » Sat Nov 09, 2019 4:01 pm

It may be worth a repair kit, depending on what ecu your using, you may be able to switch that single cylinder to petrol to try and isolate which one is the problem (probabbly worth doing all of them if repair kit is justified, but you can also swap injector wiring and pipes around to prove its the injector causing the problem). What injectors are you using? Not all are rebuildable, and some need adjustment when they are rebuilt

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Re: Cutting out when on gas

#8 Post by Gilbertd » Sat Nov 09, 2019 6:40 pm

Are you sure it's a ticking from an injector and not the sound of a arc from one of the coils? As you've had to get brutal with them it's possible that you've cracked one.
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Re: Cutting out when on gas

#9 Post by Brian_H » Sat Nov 09, 2019 11:06 pm

Gilbertd wrote:
Sat Nov 09, 2019 6:40 pm
Are you sure it's a ticking from an injector and not the sound of a arc from one of the coils? As you've had to get brutal with them it's possible that you've cracked one.
That was along the lines of what i was thinking as well. Equally if its misfiring badly enough to be logged by the petrol ecu with a corresponding cylinder, you could swap coils round to rule them out. Worth stating that a ignition fault will be more noticeable on gas than petrol as well.

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Re: Cutting out when on gas

#10 Post by HMJonesy » Tue Nov 12, 2019 4:07 pm

HI all thanks for the replies.

Today i had to change a coil due to a new misfire and has made a huge difference but still not running on gas. The ticking is defo from the injectors and im not sure what brand they are. I can take a photo but no labels on them so unless you know i have no idea. The ecu is a stag 300-8. Not the best of images though sorry

Image

Image

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Re: Cutting out when on gas

#11 Post by LPGC » Wed Nov 13, 2019 8:47 pm

Injectors look like Rail IG Apache to me, not an injector I'd ever advise/fit, not good in performance or reliability, in fact I haven't found any Rail brand injectors to be much cop. I've swapped loads of IG1's that have failed early on installs fitted elsewhere, several sets in the yard at the moment I need to sweep up and bin. If you're hearing a ticking noise from some of them more than others it's likely some have failed and others are getting that way. But if you swap to a different type you'll need to do a full re-calibration. Also if you intend on swapping injectors to a different type check the internal diameter of the pipes from injectors to manifold, some of the Apache's used 4mm outlets and these days choice of injectors with 4mm outlets is limited, today the standard is injectors have 6mm outlets. On at least some of the pipes between injectors and manifold you should be able to see writing telling internal diameter such as e.g. DN4 / DN6. If you want to swap injectors and have DN4 pipes you could swap manifold 'spuds' (brass bits) to 6mm fittings instead of existing 4mm fittings. Valtek type 30 injectors are still available with 4mm outlets, not a good injector at all but better than the Apache's. I wouldn't advise Valtek type 30's though, some have internal restriction of 2.5mm and you'll likely need higher flow than 2.5mm internal restriction or 2.5mm nozzles would mean.
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Re: Cutting out when on gas

#12 Post by HMJonesy » Fri Nov 15, 2019 10:21 pm

Had a look at the hoses and they don't bare any marks as to what diameter they are. Looking at the marks on the injectors and I'll agree with them been Rail IG Apache. If I was to get them changed what exactly is entailed and how much am i looking at roughly.

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Re: Cutting out when on gas

#13 Post by LPGC » Sat Nov 16, 2019 4:43 pm

Pull a hose off an LPG injector (hose that runs to the inlet manifold not a wider diameter feed pipe) and see if you can slot an M6 bolt thread inside it, it you can those pipes will be 6mm internal diameter and you'll be able to use a wide range of injectors (not just a small subset of possible replacements including the original type) without changing the pipes.

Some of the Stag 300 ECUs were supplied with an inline type pressure sensor (in the main feed pipe between reducer and injectors) which may or may not incorporate the gas temperature sensor, some Stag 300's were supplied with a remote temp sensor which wouldn't incorporate the gas temp sensor. If the temp sensor isn't incorporated in the pressure sensor the temp sensor may be a discrete unit fitted in the main feed pipe or the temp sensor may be fitted to the injectors. If the temp sensor is fitted to the injectors any replacement injectors would also have to be fitted with a gas vapour temp sensor or a discrete inline type would have to be fitted.

All things that could affect the costs of replacing the injectors with a different type. As said, there isn't just the physical stuff (supply and fit) there's also the software stuff (calibration) to do. The cheapest and simplest thing you could do would be swap like for like, fit yourself and hope calibration is OK, that should cost about £150 as the model of Apache injector you have aren't particularly cheap (or good value in terms of performance and reliability versus cost imho). A pro like myself could swap in far better injectors that are also less expensive, hopefully without having to change injector to manifold piping or mess with gas vapour sensors, but would involve having to do a full recal (which would probably be a good idea even if you fitted same injectors anyway). Price might be a bit more than the £150 but you wouldn't have to do the fitting or calibration yourself and should make for a better setup with longer lasting injectors.
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