Thread: Backfire Protector Valves (and a couple of other questions)

Originally Posted by 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

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.

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 !

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

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.

1. 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!!!!
2. 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.
3. 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
4. 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!"

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.

Originally Posted by 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.

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.

Thank you!

I will start Sunday & post a few photos.

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?

LPGRR 001.jpg


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