Backfire Protector Valves (and a couple of other questions)

[sam_d]

My MAF meter on my 1997 V8 D1 is on its way out. I discovered recently this is probably due to a small backfire. I was also told that it only takes a very small backfire (one that might not even be noticed) to damaged the MAF meter.

When I asked when these small backfire might occur I was told that it would probably be when the engine changed from petrol to LPG before the mixer (or whatever) had been warmed up properly. At the moment my LPG supply automatically switches over when the engive revs reach about 1500rpm regardless of the engine temperature. I was told this was perfectly okay when I got the system fitted but now I hear otherwise.

So, I have some questions:

1. How small can a damaging backfire be? Could they happen without you even beng aware of them?
2. Should I wait for the engine to warm up on petrol for a few minutes before switching over the the LPG?
3. Backfire Protector Valves - do they work? Are they worth bothering with or are they snake oil like Hyclones etc?

Thanks in advance!
Sam

[bee utey]

My MAF meter on my 1997 V8 D1 is on its way out. I discovered recently this is probably due to a small backfire. I was also told that it only takes a very small backfire (one that might not even be noticed) to damaged the MAF meter.

When I asked when these small backfire might occur I was told that it would probably be when the engine changed from petrol to LPG before the mixer (or whatever) had been warmed up properly. At the moment my LPG supply automatically switches over when the engive revs reach about 1500rpm regardless of the engine temperature. I was told this was perfectly okay when I got the system fitted but now I hear otherwise.

So, I have some questions:

1. How small can a damaging backfire be? Could they happen without you even beng aware of them?
2. Should I wait for the engine to warm up on petrol for a few minutes before switching over the the LPG?
3. Backfire Protector Valves - do they work? Are they worth bothering with or are they snake oil like Hyclones etc?

Thanks in advance!
Sam

1. I have seen a goodly number of land rover MAF sensors survive frequent large backfires without suffering unduly. I have seen others fail that have never seen a backfire. They are fickle. Don't fret too much over this one. Cleaning them regularly seems to be a better idea.

2. Most gas systems with auto changeover have an adjustable timer that allows the petrol to run on for a short time after the gas comes on. This prevents backfires due to lean mixtures on changeover. It may need adjusting, if you can find the adjustment point. Hot or cold shouldn't matter.

3. Backfire valves are essential on flapper type air flow meters, but I gave up fitting them to hotwire maf systems because of (1) above. Also they MUST be mounted downstream of the gas mixer, ie between the mixer and the throttle body. Also they restrict the airflow further and cut power by 10 to 20% because of the limiting size of the flap inside.

[ozscott]

I put Em on my airbox. They work ok but I think I need a couple on the base. My 2 are on the lid. The box base is weak. Cheers. My Maf has not suffered on the d2. I put them on so I didn't need to keep buying second hand air boxes !

[It'sNotWorthComplaining!]

I had one maf go on a back fire, then another was ok after a back fire that blew my airfilter box to pieces . go figure

[Gromit3528]

After suffering a number of LPG backfires on my 95 3.5 V8i Discovery i was given a few tips that served me very well.

Don't overtighten the hose clamps on the air hose between the MAF and the intake. You should still be able to rotate the hose on the MAF boss. If you get a backfire it just blows the hose off rather than shredding it or blowing your airbox to bits. All you then have to do is refit it it if you can find the hose clamp!!!!
Get some Magnecore Ignition leads. The higher resistance of LPG causes much higher voltages to appear in your HT system so causing breakdowns (HT leakage) and backfires. The Magnecore leads are well able to withstand this increased voltage and provide greater reliability.
Fit an RPI ignition amplifier with dual timing. When running on LPG the ignition is advanced to help with the slower burn time of LPG. This provides much better efficiency and better Kms per litre. It also provides a solid fat spark at your plugs so the LPG ignites better. Its so good you can even open up the plug gaps a bit more to really get that LPG igniting reliably in the cylinder. Don't do this if you haven't fitted the Magnecore leads though, they really complement each other
If you do all this and check out your Distributor and ignition timing, Backfires will be a thing of the past and you'll get much better efficiency from your LPG.
Cheers

Gromit

"You just gotta be lucky sometimes!"

[geodon]

I have just has a backfire disable my '92 dual-fuel RRC.

Oh the ignomy! I had to go out with my beloved Grey Fergy & tow it in with a big trailer load of straw attached. Harry Ferguson must be ****ing himself laughing somewhere up in the sky.

Has there been a post with pictures that I can refer to to do the repair?

I CAN do stuff but this will be the 1st RR job.

[bee utey]

I have just has a backfire disable my '92 dual-fuel RRC.

Oh the ignomy! I had to go out with my beloved Grey Fergy & tow it in with a big trailer load of straw attached. Harry Ferguson must be ****ing himself laughing somewhere up in the sky.

Has there been a post with pictures that I can refer to to do the repair?

I CAN do stuff but this will be the 1st RR job.

Start by removing the air hose/s from the engine to the air cleaner, look for large splits in any rubber component. An idea as to what your set-up looked like would help... every gas system will be different to some degree.

[geodon]

Thank you!

I will start Sunday & post a few photos.

[geodon]

As a complete RR & LPG novice, I need some help in understanding what's going on re air/fuel intake.

Can someone identify componenents 1-6 please?

40077


Hmmm! It appears I can only do one at a time?

[geodon]

40078

[geodon]

40079

[geodon]

40080

[bee utey]

1. Impco model L gas converter
2. MAF or mass air flow meter. Controls petrol mixtures and is original car part.
3. Impco model 200 mixer (or generic copy) also known as cork-in-the-air-intake, AKA boston strangler :wasntme:
Rubber bulb at back of engine: cruise control actuator

One tag appears to be on the engine fumes breather. Can't read all the tags.

When you click on the pics you get bigger versions. Next time do the tags with black texta. You can do up to 5 attached pics per post. Use the "manage attachment" button below your post window.

[geodon]

Easily seen in the 3rd photo:

#6 is the big casting (with "3.9" embossed) on top of the motor bridging the heads so it has to be the intake manifold for air?

#5 is an electrical device just before the inlet throat of the casting: oxygen sensor? air temp sensor?

So! The converter is a heat exchanger to convert fuel from liquid to gas.

MAF is self explanatory.

The mixer is thus the de-facto LPG carburettor?

GEEZ! With such a big volume of air/LPG always in the system, no wonder they pop-off with extreme prejudice! No surprise injected LPG systems are getting popular?

I thought there was some sort of an interface between the two systems ie separated by some sort of diaphragm?

So, where is the damage done during backfires?

[geodon]

OK I can get that a backfire will inactivate the LPG supply but why does it conk out on petrol as well?

[bee utey]

No.6 is then the plenum chamber
No.5 is probably the throttle position sensor (TPS) and has a round 3 wire plug.
Interface? Diaphragm? To run on gas you disconnect the injectors using a relay or two. They will be cut into the main wiring loom somewhere between the engine and the ECU inside the vehicle.

If you remove the mixer, unscrew the 5 screws holding the round cover on, you will see a diaphragm and spring. They are what vary the gas flow relative to the air flow. If the mixer is jammed shut no air will enter the engine. The cover can be warped and not seal the diaphragm, preventing it from rising under vacuum generated by throttle opening and allowing air to pass through on either fuel. If the mixer has shattered/jumped off no air will be metered by the MAF and the engine will not run well.

Do get yourself a workshop manual, click the "shop" tag at the top of the page and order a CD manual called "RAVE" suitable for your vehicle.


Easily seen in the 3rd photo:

#6 is the big casting (with "3.9" embossed) on top of the motor bridging the heads so it has to be the intake manifold for air?

#5 is an electrical device just before the inlet throat of the casting: oxygen sensor? air temp sensor?

So! The converter is a heat exchanger to convert fuel from liquid to gas.

MAF is self explanatory.

The mixer is thus the de-facto LPG carburettor?

GEEZ! With such a big volume of air/LPG always in the system, no wonder they pop-off with extreme prejudice! No surprise injected LPG systems are getting popular?

I thought there was some sort of an interface between the two systems ie separated by some sort of diaphragm?

So, where is the damage done during backfires?

[geodon]

1st exam showed that the hose bet the MAF & the mixer has been blown off at the mixer end. Easy.

The MAF was wobbly- the mount was a typical crude LPG installer thingy so I tightened it up a bit after detaching the 5 pin plug.

It ran well then I realised I forgot the plug & when I connected it, it was just as crappy as before.

What does denying the MAF power mean? Does it have a failsafe setting that over rides the problem?

Are they fixable? I notice there are MAF cleaners available. Is it possible the backfire dislodged some debris & affected the sensors?

[bee utey]

MAF sensors fail for all sorts of reasons, and there's nothing to lose by cleaning one. Use care, MAF or contact cleaner, no harsh solvents, no brute force air jets.

Also a MAF disconnected enables the ECU's "limp home" mode and it will run badly when you reconnect while running. Switch off the engine and only restart with the MAF plugged in.

[geodon]

Dismantled the MAF unit to gain access to the bypass with the sensor wires.

Gave them a good blast with CRC MAF Sensor cleaner ( 25 BUCKS for what I'm certain is nothing but Iso-Propyl Alcohol!?).

Fired up & goes a treat on petrol but "not a sausage" on LPG.

Time to get intimate with an Impco 200 series mixer, I guess. I got a good download from Impco with an exploded diagram & a parts list.

Am I safe in assuming there are all sorts of gizmos that stop the stuff coming out when I undo fuel lines under the bonnet? I use golf tees to plug petrol lines when they start to flow but I don't think that's gonna cut it for LPG, they're too damn big.

[bee utey]

Time to get intimate with an Impco 200 series mixer, I guess. I got a good download from Impco with an exploded diagram & a parts list.

Am I safe in assuming there are all sorts of gizmos that stop the stuff coming out when I undo fuel lines under the bonnet? I use golf tees to plug petrol lines when they start to flow but I don't think that's gonna cut it for LPG, they're too damn big.

If you don't muck around with the high pressure copper or flex line from the tank/s to the converter you won't need to plug anything. The 1" ID gas hose from the converter to the mixer will have a trace of gas in it at best. Disconnect this hose, switch on the gas and the ignition. If gas rushes out of the converter then the converter needs a kit or replacement. If you press the small button in the middle of the converter and a bit of gas flows out then it is normal. Do this in a well ventilated place of course. If nothing comes out at all you may have knocked a wire off a gas solenoid. Then proceed to taking the top off the mixer. There's not much in one.

[geodon]

OK, in the interest of avoiding a chk-chk-BOOM scenario:

1: The high pressure liquid feed from the tank.

2. A cut-off solenoid

3. The Gas feed to the mixer

4& 5 hot water from cooling system.

So if I unhook the hose @3 & press the springloaded button in the middle of the converter, I should get a gas supply at the spigot 3?

Don't I have to energise that solenoid? I mean there can't be gas coming out with just the ingnition switched on. Isn't there a safety circuit that detects the engine turning over eg running or cranking to start? Otherwise, if the engine stalls & (or an accident occurs) and the ign is left on that would mean the engine bay fills with gas. chk-chk-BOOM??

[bee utey]

OK, in the interest of avoiding a chk-chk-BOOM scenario:

1: The high pressure liquid feed from the tank.

2. A cut-off solenoid

3. The Gas feed to the mixer

4& 5 hot water from cooling system.

So if I unhook the hose @3 & press the springloaded button in the middle of the converter, I should get a gas supply at the spigot 3?

Don't I have to energise that solenoid? I mean there can't be gas coming out with just the ingnition switched on. Isn't there a safety circuit that detects the engine turning over eg running or cranking to start? Otherwise, if the engine stalls & (or an accident occurs) and the ign is left on that would mean the engine bay fills with gas. chk-chk-BOOM??

Basically correct but I told you (in the post below) the order of events which will energise the solenoid. It will open for around 1 second when you turn on the ignition and gas switches. In some installations you might have to energise the starter for a moment.

If the converter is stuffed you are safely away from the converter and can switch it off pronto. If the converter and electrics work as advertised you will then have some gas trapped in the converter which will be released on pressing said button.

PS I do have some spare Impco bits if you find yours are faulty.

[geodon]

Well now it won't run on petrol again despite a successful 10km test yesterday run after cleaning the MAF sensor wires. So the MAF unit must have been in its death throes or have an intermittent fault? Is this what they do when they play up?

I can get one in the states for $US332 + an extortionate amount for the pirates at UPS!

Maf - Auto Parts Warehouse (http://www.autopartswarehouse.com/search/'searchType=global&N=0&Ntt=maf&submit)=

Local source?

Can anyone loan me a serviceable unit for a diagnostic check before I invest in one? I'm in the Melbourne CBD or Geelong or I'm prepared to pay postage both ways & there's a decent bottle of McLaren Vale shiraz in it for you. PM me your email.

[bee utey]

Check for spark, fuel pump etc as the engine will run with a faulty/disconnected MAF as you found out. If spark is present the gas should be easy to get going. You should probably adjust the plug gap to 0.7mm before you try the gas again, it reduces the chance of backfiring.

[geodon]

BTW Bee Utey, mate you were dead on re the Impco Mixer! 1st Order Low Technology. Just a spring loaded diaphragm (VERY intact I might add!) that lets in more gas as more air flows thru and compresses the spring.

I checked the converter: ign on & press the button gives me ONE puff of gas so there MUST be an aditional circuit that detects the engine turning or cranking before letting gas thru.

BUT what is different this time is it's JUST as bad with the MAF disconnected, ergo something is "stuck" in one setting. Check this ref under "Cold Stall".

Range Rover Remedies (http://www.rangerovers.net/rremedies.htm#mafsensor)

OR do I need to reset the ECM??

There are 5 male pins on the MAF & 4 female connectors on the plug. I have a Multi-Meter. Can I test it? Isn't there a "Faults" display thingy somewhere? My Rave1 CD is in the mail.

[bee utey]

The most common problem I used to meet with D1/RRC dual fuel engines was the partial or complete failure of the ignition amplifier. I developed a cheap repair method, shown in this thread:

http://www.aulro.com/afvb/technical-chatter/96950-lucas-ignition-amplifier-replacement-bosch-024-a.html

From your link:


The ignition amplifier module (http://www.rangerovers.net/rremedies.htm#ignition) is a notorious cause of hot stalling and stuttering. Dean Sonneborn (DSonneborn@aol.com) found the heat buildup under the hood when his 1990 RR was not moving (eg stopped at traffic lights) caused his ignition amplifier module to fail intermittently, stalling the engine. The faulty unit was so sensitive to temperature that even a minute or two of cooler air provided by opening the hood got it working again.

Check the ignition is working AOK first and foremost.

The gas system uses a connection from the negative side of the ignition coil to determine whether the engine is running and needs gas. No spark = no gas flow (after the 1 second first on-period).

AFAIK you don't need to do anything to the ECU. It's pretty stupid and works when everything is plugged in and correct.

[geodon]

Well that's food for thought- the ign system may have failed as I changed from petrol to gas coincidentally.

Where is the OEM ign amp on my '92 RRC? It's not near the coil.

I unhooked the HT lead for the top of the cap & got a steady stream of fat sparks anything up to 12mm from an earth as the eng cranked which may not mean much!

I got it to run on petrol (reasonably well too) for a while with the FAM unhooked but I could not reproduce it despite trying repeatedly.

I guess that's what an intermittent fault is about!

BTW, I run a Bosch dist on my MGA.

Huns 1 (heading for 2?), Prince of Darkness 0.

[bee utey]

Where is the OEM ign amp on my '92 RRC? It's not near the coil.

https://www.aulro.com/afvb/

It's where the wires in my conversion connect to the dissy. Remove amp, connect wires, fit amp&coil away from the heat.



I unhooked the HT lead for the top of the cap & got a steady stream of fat sparks anything up to 12mm from an earth as the eng cranked which may not mean much!

Try this again with the dissy cap off, aim the lead at the centre of the rotor button. If spark jumps to the brass strip in any significant way your rotor button could be fried. You can use a XF Falcon rotor instead of aftermarket cheapie RR replacement. It's Bosch part no. GB864, works the same but looks quite different.

[geodon]

These don't look real healthy to me!

The end of the rotor is SINTERED and so are the terminals inside the cap.

Bee Utey, I assume that is the OEM Ign Amp under the black connector?

Well I will try a replacement rotor & cap and see what happens. Can't quite see how they could fail so suddenly but their condition warrants replacement anyway.

So a new Lucas cap & a Bosch GB 864 rotor is the go? Or is there a good aftermarket cap as well?

[geodon]

I forgot to mention the rotor came off real easy & there is some sort of treacly grease under it. Is that the "anti-sieze" that ppl suggest goes there?

[bee utey]

Your dissy cap terminals should be OK with a quick scrape off. What about the inner surface of the cap though? That looks like moisture droplets. If you have got water in your dissy it will only run occasionally, as moisture condenses and re-evaporates inside the cap. Give it a darn good polishing with a soft dry rag and refit it. If moisture reforms you will need to leave the cap off so any moisture in the dissy can evaporate.

Don't know anyone who puts "anti-seize" under their rotor. I use a drop of engine oil once every 10,000km.

The ignition amp is where I said it would be.

The rotor is a substitute not listed in any parts book, as it has been tested by individual owners only. The cap is whatever part is listed in a catalogue, nothing else comes close.

[geodon]

The first attempt to get sparks accross from the coil HT lead to the exposed rotor was inconclusive then I remembered what an old auto elect told me: "If you are looking for sparks, do it in the dark!"

I repeated the test with the garage door down & the lights out & sure enough there was a thin stream of orange sparks from the end of the lead to the centre of the rotor. Ergo a leak to earth= a misfire. It wasn't a huge loss but probably enough to cause idling problems & misfiring under load.

It's Sunday arvo so I'll try a new rotor next week.

[geodon]

Hey Guys!

This Bosch GB 864 rotor is a VERY tight fit. In view of the Stuck Rotor Syndrome, I was worried so I gave it the hot air gun for a while & it was a bit better so I assumed it would be ok on a hot engine & wear itself in.

There was no HT bleeding thru the new rotor so I was hopeful.

But, while it now runs OK with the FAM disconnected & starts very easily, it still won't idle under 2000rpm. & its much worse on LPG than petrol, wuth lots of little backfires.

Comments?

[bee utey]

Hey Guys!

This Bosch GB 864 rotor is a VERY tight fit. In view of the Stuck Rotor Syndrome, I was worried so I gave it the hot air gun for a while & it was a bit better so I assumed it would be ok on a hot engine & wear itself in.

There was no HT bleeding thru the new rotor so I was hopeful.

But, while it now runs OK with the FAM disconnected & starts very easily, it still won't idle under 2000rpm. & its much worse on LPG than petrol, wuth lots of little backfires.

Comments?

That's funny, I've not had a problem fitting the GB864. There must be a minor variation somewhere.

A hose fallen off or split open? Look around the back of the inlet manifold at the idle air bypass hose.

[geodon]

Well done mate! T'was blown clean off! Idles great now. Too late for a test run. Will report tomorrow.

Geez! I haven't had so much fun since my 1st major job: tracking down a misfire 40 years ago on my 1st car: a '56 Beetle. Not a good ending: it was a cracked head!

My Synopsis:
The rotor partially fails.
Random HT current bounces around under the dist cap. It randomly fires spark plugs sometimes when inlet valves are open. No biggie on petrol, there's no fuel in the intake!
Being a frugal chap I switch to LPG. KERBOOM! an almighty backfire blows off the inlet hose between The MAF & the LPG mixer & the air idler hose.

Thanks again!

[geodon]

Test run went fine.

I took of the cap & the rotor went off & on no problems confirming that it was "newness" that made it tight. A burr that I did not see?

It still has one feature that puzzles me.

It starts 1st hit on LPG dead cold but refuses to do so when hot. I have to switch back to petrol then to LPG when on the move again. Surely this is not some wierd safety thng?

[bee utey]

Test run went fine.

I took of the cap & the rotor went off & on no problems confirming that it was "newness" that made it tight. A burr that I did not see?

It still has one feature that puzzles me.

It starts 1st hit on LPG dead cold but refuses to do so when hot. I have to switch back to petrol then to LPG when on the move again. Surely this is not some wierd safety thng?

The petrol assist timer may be adding too much petrol during hot starts. If you could find it they usually have an adjustment on the box. Don't ask me where it is, you will have to find it yourself. It could be built into the changeover switch, or fitted near the relays that shut off the petrol.

Try cranking the engine and slowly pressing the accelerator to about 1/4 down as the engine spins over. This shouldn't cause any problems. Don't floor the pedal before cranking of course. Just squeeze it after cranking has commenced.