Engine warm re-starting/backfiring problems?

[MR-Scott]

Well, after running like clockwork for a few years now, it would seem the old MK1 (G reg) has developed a starting issue

Basically as an example, if i start it from cold (usually starts first time), then drive to the petrol station, fuel it up, then try and re-start it, it refuses to fire properly and splutters, coughs and backfires rather loudly. To be fair, it sounds like a cannon going off and gets rather embarassing especially when people start running for cover!
It sounds as though every now and then whilst turning it over it will try to fire, and produces a random coughing (pressure/compression sound?), followed by the bangs.
Ive had to leave it for nearly half an hour at a time before it fires up again.
I have also noticed that if whilst stationary, you keep revving it slightly for a short while, it struggles a bit then, and almost stalls (if i stop the engine now and try and restart, it just does the above). It has done this mid-drive a couple of times too.
I need the car for work as the Mrs is using our family car to drop the baby off at nursery, so this is in need of fixing rather quickly!

Any ideas guys? All help appreciated......

Cheers,
Scott.

[jon_st205]

Most likely to be ignition related - rotor arm/cap/leads/plugs - good starting point, and cheap to do. Doubt it's lack of fuelling if it's backfiring and popping

[pk_090]

You havent welded a spark plug into the exhaust and connected to the dizzy and a switch?
Starting points other than mentioned above, check both cam and dizzy timing, check for exhaust leaks, and such. Its it making the noise though inlet or exhaust?
Alex

[MR-Scott]

You havent welded a spark plug into the exhaust and connected to the dizzy and a switch?
Starting points other than mentioned above, check both cam and dizzy timing, check for exhaust leaks, and such. Its it making the noise though inlet or exhaust?
Alex

I wish it was something I created!........ At least if the problem doesn't get fixed, I should be able to sell the car no problem to a farmer as a bird deterrent!, lol
Sounds like its coming from both, but that's only what I can hear from inside the car when trying to turn it over.
Could it be a coil issue, breaking down when the engine is warm?

Cheers,
Scott

[pk_090]

I think a simple starting point would just to check all the free items first. Check the plugs have correct gaps and clean and adjust if needbe,check the ht leads are corrected. Cable tie them all together and try and take them away from the engine cam covers. I had a misfire on one of my old bikes where the leads were insulating against the block, only saw it when working on the bike at night and saw the flashes against the block. Could be something really simple! What fuel are you running it on?
Alex

[MR-Scott]

Standard unleaded mate. I only use V-Power in my turbo.
I'm going to order new plugs, leads and dizzy cap/rotor arm from Camskill tonight, and see if that makes any difference.
What plugs do they prefer? Ngk (basic £2.99 jobs), Denso iridium, Ngk platinum......etc?

Cheers,
Scott.

[Lauren]

I've always sworn by the OEM Denso plugs from Toyota. No more expensive from what I recall compared to NGK's and pre-gapped correctly of course.

I admit though, I only use all OEM when it comes ignition components. Expensive but I've never had an ignition related problem in all my years of messing around with 4AGE's.

[pk_090]

Last time used genuine cap and rotor and ive got ngk iridium in and had no problems with them whatsoever. I must admit mine coughs and splutters abit on 95 but not on vpower or momentum.
Alex

[LimeyMk1]

I always used NGK coppers BCPR6EY-11 if I recall correctly, may be 5EY-11 for stock replacement but I always used 6s. They will be pre gapped too.

A couple of other things to check are the vacuum lines for leakage and the cold start injector (may be stuck open).

[aw11rally]

I always used NGK coppers BCPR6EY-11 if I recall correctly, may be 5EY-11 for stock replacement but I always used 6s. They will be pre gapped too.

A couple of other things to check are the vacuum lines for leakage and the cold start injector (may be stuck open).

Could be something to do with cold start as it sounds like it's too rich, what about water temp sensor?

[MR-Scott]

Cheers all.
Where would I find the cold start injector and water temp sensor?
It only does this when its warm, which I'm thinking then could be the engine still thinking its cold, chucking way too much fuel in?

Cheers,
Scott.

[LimeyMk1]

Cold start injector is on the inlet manifold, it's pretty easy to ID as it's the only component on the manifold with a fuel feed. Just unplug the electrical connector and see if it helps, nice easy one to eliminate from the potential problems.

To be honest you could happily run without it for most of the year.

I think the water temp sensor is on the left side of the engine as you look from the back of the car on the coolant outlet on the head. If I recall correctly the outlet has the fuel lines bolted to the top of it or is under that point. I'm not sure how to test it but will have a look in the manual and see if there's any guidance.

Sensor has a white connector in this piccy:



Down from the bracket that holds the speedo cable.

Piccy tea leafed from Jimi's site.

[LimeyMk1]

Instructions for testing the coolant sensor, got a decent thermometer handy?

[PW@Woodsport]

Amazed nobody has suggested a basic fault code pull as the starting point, that's at the very top of the diagnostic flow chart tree, could be this, could be that.....the ECU could have the answer right there without guesswork and is the simplest thing to check first.

I have several good reasons it would suffer those exact symptoms but pull your codes first, i wouldn't want to set you off in the wrong direction or cost you money with a guess.

Bridge T and E1 in your diagnostic port, count the check engine light flashes and report back, if it flashes continually there are no codes.

If it throws a code 4 it's your EFI temp sensor, but could be anything.

[MartG]

I think the water temp sensor is on the left side of the engine as you look from the back of the car on the coolant outlet on the head.


Piccy tea leafed from Jimi's site.

The cold start system uses a separate temp sensor from those used by the engine ECU. It's the black one on top of the thermostat housing ( lower centre of pic, to the left of the orange hoses and to the right of the white bleed valve )

[MR-Scott]

Cheers for the help guys
Hopefully ill get some free time today to check the above suggestions!

Scott.