Thread: Severe backfire - then rough running

Originally Posted by Sbrrc

Hi all

93 RRC was running beautifully. Smooth idle, smooth acceleration etc - however after a 40 min run, had a pretty big backfire when accelerating from stop at lights - then rough running for the next 5 minutes till I got home. Now it wont kick over. Any immediate thoughts. Stuck valve?

I'd recently adjusted timing, but as I said, was seeming running much better - at least for 40 mins.

Trying to sort it all out myself, as every mechanic I try just seems to charge money without fixing anything.

Any pointers would be hugely appreciated.

Cheers
Simon

Petrol or LPG?

Originally Posted by Tins

Petrol or LPG?

Was running perfect on both.

then, was on LPG when it backfired.. but switched to petrol, ran rough..

Have since got it started and it runs, but terribly, on both LPG and petrol. So I don't think it a fuel issue.

Originally Posted by Sbrrc

......I'd recently adjusted timing, but as I said, was seeming running much better - at least for 40 mins................

Cheers
Simon

I'm guessing the points have slipped?

Originally Posted by Sbrrc

Was running perfect on both.

then, was on LPG when it backfired.. but switched to petrol, ran rough..

Have since got it started and it runs, but terribly, on both LPG and petrol. So I don't think it a fuel issue.

I asked because I've had the issue before on LPG. Not on a RRC, but a Ford. The backfire can be caused by a vacuum leak, and then the backfire will blow a hose off, or blow out a valve or sensor on the manifold somewhere. It's difficult to be more specific, as no LPG installs are the same, but I'd be concentrating on all the hoses on the intake side first. A vacuum leak can cause rough running and hard starting on both fuels.

My guess, anyway. Good luck.

EDIT: On the Ford the backfire actually split the intake runner, which was hard to spot, so it kept doing it.
RL may be correct as well, and the timing has slipped.

If you do a search on this topic I think you'll find the MAF (?) will be ted.

People on lpg with stock RRC fuel injection started using a neoprene sock downstream of the MAF to let the pressure off before it was destroyed.

IME nearly all backfire probs are ign related................ in my case the leads.

One spectacular one cracked the snout on the Chevy starter and one or two teeth off the flywheel.

Never had a problem after going to Bosch induction leads and I always start it on gas.

DL

Before you wholesale exclude the ignition, look at my honeymoon's over thread.

the rough running you are seeing is indicative of a failing module where the dwell control has been completely munted through back EMF. Possibly from too much timing.

12deg at idle is all you need on a 14cux.

time to test your reluctor, module and coil primary/secondary, reset timing to factory spec, then start on gas. That will rule out MAF as being an issue.

If it's still running rough and your vac lines are in tact, then you need to check dwell angle, and chances are the module's pooped itself.
The coughing stumbling farting lack of advance or no rpm increase on throttle application point to module and dwell angle - IS the module wired correctly? if it's wired backwards it will behave like that...

So:
1. static timing
2. static advance
3. reluctor, module, coil measurements
4. vac lines
5. run on gas - check dwell angle and idle timing
6. check full advance and rpm.
7. switch to petrol and check maf.

Originally Posted by Sbrrc

Hi all

93 RRC was running beautifully. Smooth idle, smooth acceleration etc - however after a 40 min run, had a pretty big backfire when accelerating from stop at lights - then rough running for the next 5 minutes till I got home. Now it wont kick over. Any immediate thoughts. Stuck valve?

I'd recently adjusted timing, but as I said, was seeming running much better - at least for 40 mins.

Trying to sort it all out myself, as every mechanic I try just seems to charge money without fixing anything.

Any pointers would be hugely appreciated.

Cheers
Simon

Morning
Spotted your notes. I had one of these do the exact same thing. I found it had blown a vaccuum hose off which created a huge air leak. The engine ran really bad and I was lucky to get the thing home. It took quite a bit of tracking down but we eventually found it.
Sounds pretty simple I know but start with that and go from there.
Kind regards

Could be a combination of things that others have said.

On our Mitsy work vans,which we had years ago,LPG/petrol,it was usually plugs and leads.Always use the best quality leads and plugs available,or the problems would continue.