1998 Toyota Previa Misfire

[TeeMyob]

Hi,

My first time here and my first ever LPG conversion.

So, some history.

I’ve run TOYOTA previas since 1996. I now still have two .
A 1998 and a 1999.

So the 1998, 2.4, 4 cylinder, mid engined with 100,000 miles on the clock. I have just in November had converted to LPG By an installer.

Drove it down to Spain where I keep it for 6 months every year. All was okay until this week. Used the car one morning and afternoon, all was fine. Went out in the evening and it suddenly started to miss fire and loose power.

Problem is, it’s holiday time and everywhere is closed here in Spain.

I took the engine cover off, checked all the leads etc, all seems okay. Even took iridium plugs out and they seem okay. Rang installer who could not suggest anything other than clarify it misfires on both LPG and petrol.

So I runnit down to repsol and put some posh 98 octane petrol in and switched off the gas
LPG . I’ve run it on petrol for about 80 miles and it’s improved a lot. Switch lpg on and the fring is nursery or stall (automatic).

Any suggestions welcome please ?

[JX350]

Hi,

If you can't get the installer to fix this then the first step I would do is find out which cylinder is misfiring. That would help you identify the cause. Is your engine management light on? If so then you might be able to get the fault code with a suitable cheap reader.

Thanks,

Chris

[TeeMyob]

Thank you.

The engine management light is not on.

I have been looking at cheap readers, I have an old diagnostics 17pin OBD.

Not sure what to buy. eBay is useless in Spain due to its shockingly poor postal service.

Cannot seem to find anything reasonably priced on amazon.es

[TeeMyob]

Booked up n with garage who suspect coil pack

[LPGC]

Some late 90's Japs have standard looking OBD2 ports but a normal OBD2 won't work because the port is actually OBD1 or JOBD that's just been wired to use an OBD2 socket. An OBD2 scanner might work or might not..

if the misfire is constant you could use an old-skool method of finding which cylinder is misfiring... remove each cylinder (in turn) HT lead or disconnect it's coil pack... if the engine loses fire on another cylinder you've got the wrong cylinder, if the engine runs the same you've found the one with the misfire.

Edit - just noticed you've said yours has coil packs.... So find the cylinder with the misfire and swap it's coil pack with another cylinder, if the fault moves to the other cylinder you've pretty much confirmed the coil pack was the problem.

[TeeMyob]

Thank you.

The garage, without seeing the 1998 previa had said “probably a coil pack”.

I took it in today. But, they said they cannot attempt to repair it as it’s too old. They said their diagnosis computer will not connect to my car.

Back to square one.

[Gilbertd]

At that age it will be, as Simon suggested, JOBD. My daughter had a Jap import Toytoa MR2 of similar vintage and I bought a Creader Vi+ which can do JOBD as well as standard OBD2 and EOBD. Unfortunately the only sellers I can find aren't in the UK (https://www.ebay.co.uk/itm/Diagnosis-La ... 3836334342) and as it is an old model, doesn't appear available anywhere else. There's plenty of people selling the Vi (which doesn't do JOBD) and the later Vii which is a lot more expensive.

You could try going back to basics as Simon suggested. If it is a constant misfire, then disconnecting the feed to each coil pack in turn will identify which one isn't running. However, if it is an intermittent misfire, then it might be a bit more difficult to track it down.

[TeeMyob]

Hi,

It’s 17 pin.

A1D43FEC-5960-4C4E-AD3C-28D86E3AC045.jpeg (2.44 MiB) Viewed 4448 times

[Gilbertd]

Ahh, that isn't JOBD. JOBD uses the same connector as a standard OBD connector, just a different protocol. Never seen one like that I must admit but I doubt it will store any misfire codes so wouldn't help you anyway.

[LPGC]

Other model late 90's Toyota's have the same diagnostics port, sometimes fitted in the engine bay instead of inside the car. Not always or necessarily used with a code reader, some of the pins are probably wired directly to lambda probe signals etc. Seems to be an abbreviated pinout description in the cover? Sometimes with this type of diagnostics port you can get a light on the dash to flash error codes morse-code style by shorting a couple of pins - But don't short any pins yet, read up on this on Toyota forums before doing anything like that first. Probably best to stick to old-skool (swapping coil packs around etc) diagnostics. Some Toyotas have a similar looking port to this in addition to another diagnostics port (so diagnostics ports, one port wired to engine components so lambda sensors, an rpm signal, TPS, etc, one port to be used with a code reader).

But the garage should know how to do old-skool diagnostics.. If they don't, or if they're lazy enough to only want to get involved if they can plug something in that will tell them what's likely to be wrong in plain English, use another garage.

[Brian_H]

This might help https://www.youtube.com/watch?v=lEZ9Gl53DhQ

European cars of that age, generally don't actually light up the MIL (Check engine light) for fault codes. A lot don't even have an MIL as they weren't required until sometime around 2001.

But I think you may find it isn't detecting any misfires unless your lucky. You might find it the best course of action if its not giving you any clues, to obtain another coil pack and swap around to see if you can find the culprit. Or alternatively if you can get something like these > https://www.amazon.co.uk/Laser-2780-Ign ... B003AN1VPW to fix onto your plugs (will depend on your coil pack design, if it clips on your usually ok, but any that make contact with springs proabbly won't work) that will at least help to prove if its an ignition problem you have (4 of them allows you to compare cylinders effectively as its much clearer what you should be seeing then, and which cylinders are your problem).

TBH changing a coil pack can be quite easy, or can be a complete pain. All depends where it actually is and how easy you can access it. But nothing I'd have expected a reasonable garage to struggle with, It may be more that they want some sort of confirmation that the fault is actually a misfire and where to start looking for it.