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frankieh

XR6 turbo breakdown at high boost (not spark blowout)

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Hello folks, 

 

I have a BA XR6T, 6spd manual, JTG, liquid LPG injection and I'm having an odd issue with what seems like spark blowout at high boost (and just off idle it seems) the tune has a max of 16psi boost and advanced timing (the JTG system is why this is possible)  but it was working perfectly for a couple of years before last month.    Good idle and no spark blow out at high boost.... until recently that is.

 

First thing is that it almost certainly isn't spark blowout as I spent more than 1000 making sure it couldn't be.     The engine has series 2 WeaponX 80,000 volt coils that are powered by a JMM voltage booster that ups the input power to the coils to 14.6 volts even without the engine running.

 

The problem stemmed from back when my radiator died and I put a new one and flushed the system.  To do that I basically removed the engine side of the top radiator hose and left the car running with a hose jammed in at the other end.. I did this till the output water was nice and clean then I drained the lot and replaced with coolant.       Because there was a ton of water running down the side of the block under the thermostat housing and it never ran properly after that.    I pulled the plugs and they are nice grey/brown with no wear. (1.2mm gap which I lowered down to 1mm just in case but to no effect)  I also measured the input voltage to the coils and it is still correctly at 14.6v.    So it doesn't appear to be the spark system as it's fully functional in the same manner as it was before I had this issue.

 

Anyway, under the thermostat housing is the knock sensor and I'm wondering if the tipping of a hundred litres of water over it has caused it to have an incorrect resistance when reporting knocking to the PCM and the PCM is causing the issue because of this.

 

There are no codes reported in the system that relate to this.  I also reset KAM data to no effect.   It also does it on both gas and LPG.. it seems a little more quickly on gas though.

 

Does anyone have any experience with these systems that isn't related to overboost or spark blowout?   (it's a custom tune with 16psi max but this happens around 5psi ) nothing else on the engine has been changed anywhere near the time this happened.

 

I thought that if nobody else had any suggestions I'll change the knock sensor and check all the connectors but I'd be interested in any other thoughts.. I spent lots of money making this car fun and it's not fun at the moment.    :-)

 

regards

 

Frank

Edited by frankieh

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The first thing that comes to mind that seems like spark blowout or overboost, is a leanout past stoich.

Also if it went rich down past 9:1 you'd have similar feeling issues. It's pretty cheap and easy to check the afr.

 

The second thing is that the arc is so strong that it is leaking past the insulating boot and causing issues. A cracked spark plug can do this too.

You could drop your plug gaps to 0.7 or so, but if you're adamant the spark is still there then it'd be a waste of time.

 

The knock sensor is a sealed unit but it wouldn't hurt to check that the plug/connection is in good nick.

 

Anyhow, there's my bunch of random guesses. Hope it helps, even if it's to rule things out, that you may not have yet.

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Hello Mr Puff..   I have a wideband O2 with digital readout in my drivers side piller..   Stoich is 15.5 on LPG from memory  the AFR is usually from 12 to 16 on mine..      I also checked the plugs carefully for cracks and the boots on the coils. (plus the ceramic necks of the plugs are liberally coated with dialetric grease. )     Honestly, the spark is crazy powerful with 14.6 volts feeding 80k volt coils..   I drove around for 2 years with 1.2m gaps getting 16psi with no blowout easily.   Since it happened after flushing the cooling I'm still inclined to think I caused the issue there somehow.

 

regards

 

Frank

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It's kinda hard not being there, as this kind of symptom can be caused by many things and I can't physically check the vehicle.

 

As with any diagnosis, you track down where the last known good position was and then go from there, while keeping an open mind for random events.

 

1 hour ago, frankieh said:

reporting knocking to the PCM

 

Any chance you can log what is happening?

 

Here's something I've noticed; we're 100% sure the spark is there and you have a wideband.

 

1 hour ago, frankieh said:

just off idle it seems

 

I don't wanna lead you down the wrong path mate, but if the spark is there in some form and the afr is correct, ie: it's not leaning out just past idle , then either replacing the knock sensor/plug wiring etc and hoping for the best or logging it seems like the next step to me. I would lean toward logging it, depending on your situation.

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I don't know if it is relevant because it's had both for a year before this problem started.. but it has a big bore SS inductions throttle body and underdrive setup.      Puffwagon,  I might swap the knock sensor as I have a couple of spare motors here..  check the loom and change it and if it doesn't help I'll try logging it if I can find the relevant PID.

 

JetTurbo..      I hadn't considered that I think I'll swap that for one of the spares too.   It might also be worth disconnecting the big engine loom plug and spraying in some contact cleaner in case a dodgy connection is causing a signal drop out.   

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Gas is higher octane than petrol (amongst other things) which means it's harder to light (needs more spark). So if it is worse on gas I would be looking at a spark issue. (if it was a engine problem it would be exactly the same, a fuel issue you would expect it to do it on 1 fuel not the other) Try a new set of ford gas plugs (they're cheap @$70 a set)

Edited by 4321

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OK,  I got a code that seemed to indicate the TPS might be at fault.   Swapped it for a good one off a BF 3 wagon... code went away but didn't solve this problem.  The SS inductions throttle body is spotless and has been there for yonks so I don't think that has anything to do with it.

 

I noticed something odd though.. if the engine is spluttering down low and I put my foot in..    it splutters badly all the way up the rev range..   If I allow it to smooth out and then put my foot in..  it revs smoothly.. that's the other thing that made me suspect the TPS, but as I said.. changing it didn't help

 

I also swapped the crank angle sensor with the one from the BF3 Wagon.   That didn't help either.   Also took the big engine block plug apart and used contact cleaner and WD40 on that as I've seen weird idling from that in the past in other Falcons.. didn't help either.

 

I ordered a new set of plugs but only 5 arrived so I'm waiting for the 6th.     While I had the plugs out I put a meter on the coil rail and it was 14.4 so the JMM voltage booster is working fine and I presently don't think a 500 buck set of 80k volt weaponX coils are to blame as they are only a year or so old and were working fine.    I wondered of my overpowered ignition could have damaged the plugs insulation internally but that doesn't really fit the symptoms.

 

running out of ideas here.  anyone got any other suggestions?  I'm starting to wonder if my PCM has a dry solder joint...

Edited by frankieh

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46 minutes ago, frankieh said:

running out of ideas here.  anyone got any other suggestions?  I'm starting to wonder if my PCM has a dry solder joint...

probably just a B series thing, literally every B series turbo at the drags tonight ran like 14 second quarters. 😭

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Did you try another set of coils? they really hate getting wet. I've lost count of how many sets we change after people wash their motors & the car comes in with a miss (or backfire on old gas systems ) you said its worse on gas which to me screams ignition problem (if you buy coils we only use genuine ford as they are a known quality)

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Hi,   I've changed coils  before too.. but then I spent 560 buying what are supposed to be the worlds best coils.. used in massive boost applications.    and then I put a voltage booster on them so they get a minimum of 14volts all the time.    When I put all that in, it was the first time I had a great idle and no spark blowout on boost.   but I will try swapping in some known good ones if it's still an issue after I change the plugs I guess.

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id use genuine ford coils over those for sure, sorry. don't think voltage booster is required either, just a good tune, good fuel supply & properly gapped spark plugs.

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Well I had perfect genuine plugs and coils and if I only run petrol I'd have been fine...       But with the JTG LPG injection I can run 16PSI with advanced timing giving me 520ish HP at the back wheels.

The problem I had with the LPG is that I either had a rough idle. (small gap and LPG) or a good idle, (standard gap) and spark blow out after about 12PSI.

So I bought the WeaponX coils and they did not help at all..  as it turned out they didn't help at all because they use loads more current and voltage than the coil rail can provide.    Hence the voltage booster..      With 14ish volts to the weaponX coils, I could run a 1.1 gap for a perfect idle on LPG and still not blow out spark at 16psi.   Plus the car actually felt super smooth in a way I've never seen in another falcon before..   at least it did until my recent issues.

I don't really think it's the plugs or the coils to be honest..   my reason for that is because it isn't one cylinder that goes when it's spluttering as is usually the case with a dud coil..   the engine loses all power so for whatever reason it seems like the PCM is doing this.. I wish PCM's had a syslog of events I could look at.

 

Losing the weaponX's would cause problems because the dwell is calibrated for them in the tune.

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Hi all,

 

The problem was a dodgy sparkplug.. looked perfect from the outside but the combination of the 80k volt coils and the voltage booster must have burned though internal insulation..  put a new set of plugs in and it smoothed right out.

 

thanks for all the suggestions.

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