3rd Gen - Starting Issue & Backfire

[arif_manji]

Hi Guys,

I’m having an issue with a 3rd Gen (2.0i 4WS - B20A) I recently bought to restore. I bought it as a non runner but after a new fuel relay and fuel pump, it ran well. I tried to start it today, ran fine (apart from hunting, common when these are sat for a while) then I switched off for 10 minutes.

Then when I tried to start it again, it refuses to start and backfires. It sounds louder as the join between centre pipe and back box is broken. It feels like it just about to start then doesn’t together with a eggy smell.

I’m confuse what it could be. I’ve done the following:

- Compression test - all cylinders are really good!
- Checked plugs, they’re OK, no oil or smell of fuel.
- Engine light comes on and off fine.

Anyone know where I should start? I’ve been working on 4th gen’s more and can usually find the issue. Not that clued up on these 3rd gens.

Any advice will be greatly appreciated.

Cheers!

[Scott560]

Sounds ignition related to me. I've seen rotor caps on older cars where the car will start and idle fine from cold. Once the car warms up, the insulation in the rotor cap breaks down, and the spark doesn't go anywhere properly. The idle gets a bit rougher but it never conked out. It would then fail to restart and occasional semi-backfire through the intake.

This was an old 6cyl merc , it would start and idle from cold perfectly fine. Warmed up and just petered out. Replaced cap and and arm , new car... The car was never really driven just started up and moved on the drive way.

you might be able to confirm if that's the case by warming the car up (if it will start at all now), and then wait for the fault, then remove the cap and liberally spray WD40 inside and out, and wipe down) along with the leads. If its improved its most likely the cap/arm.

I think the 3rd gens also have an external ignitor for the coil, a small heatsink type device like an ECU, on the turret perhaps? Not sure if there is a manual with a test procedure, it may not be testable with a multimeter.

No other advice specific to 3rd gens to offer i'm afraid.

[vanzep]

I would replace the fuel filter if you have not done that already and check ignition system
eggy smell is normally cat related linked to timing being out and fuel getting dumped into exhaust - see if you can hear any rattling sound from the cat when you give it a shake.
Old fuel can smell pretty nasty as well

[arif_manji]

Sounds ignition related to me. I've seen rotor caps on older cars where the car will start and idle fine from cold. Once the car warms up, the insulation in the rotor cap breaks down, and the spark doesn't go anywhere properly. The idle gets a bit rougher but it never conked out. It would then fail to restart and occasional semi-backfire through the intake.

This was an old 6cyl merc , it would start and idle from cold perfectly fine. Warmed up and just petered out. Replaced cap and and arm , new car... The car was never really driven just started up and moved on the drive way.

you might be able to confirm if that's the case by warming the car up (if it will start at all now), and then wait for the fault, then remove the cap and liberally spray WD40 inside and out, and wipe down) along with the leads. If its improved its most likely the cap/arm.

I think the 3rd gens also have an external ignitor for the coil, a small heatsink type device like an ECU, on the turret perhaps? Not sure if there is a manual with a test procedure, it may not be testable with a multimeter.

No other advice specific to 3rd gens to offer i'm afraid.

Thanks mate. The does make a lot of sense, I did try to start after an hour but it just refused to but the backfiring was not as bad. I might just buy a new rotor arm and cap and replace them.

[arif_manji]

I would replace the fuel filter if you have not done that already and check ignition system
eggy smell is normally cat related linked to timing being out and fuel getting dumped into exhaust - see if you can hear any rattling sound from the cat when you give it a shake.
Old fuel can smell pretty nasty as well

Thanks mate. I think I’ll get a new cap, rotor arm, fuel filter and plugs and see how that goes.

[Hagland-BB4]

I would say condensation in the cap.

[wurlycorner]

Before just changing the cap (which almost certainly is worth doing) have you checked you do actually still have spark? Check that first to rule it out, so you know your 'starting point' for the fault.

One other possibility that does match the symptoms, is the timing jumped - but that's pretty drastic and hopefully you don't have that. Have you had the cambelt done yet?

[Greg]

I've never once had a prelude hunt at idle, the closest thing to a hunting idle in my experience was when the new timing belt was a tooth out but this was sorted by the garage doing the work at the time. Also if the idle control valve needs cleaning it can cause cold running issues but should still start ok and goes away when warmed up. Once you have checked ignition and are confident it's got a healthy spark next check the fuel pump is definitely running and it's not a main relay fault (hot start issues as you described and plenty of info online to check) crack open the fuel line on the fuel filter and turn on the ignition briefly to see if there is good pressure. If all is good with spark and fuel next check the engine temp sensor has not failed on the PGM-FI. It could be reading hot when it's cold and vice versa giving the ECU a false reading which will give cold start issues because the fuel map won't compensate for the extra fuel needed in cold start conditions and hot start issues if it thinks it's cold when it's hot. Not to be confused with temp gauge sensor as I'm pretty sure it has 2 sensors one for ECU and one for temp gauge.

There is an old saying in Rover V8 circles "most fuel problems are ignition based and most ignition problems are fuel based" or something along them lines anyway. I think the point was that symptoms often lead us to dead ends. Backfiring if it's not a timing issue is usually down to lean running conditions and as you said the plugs didn't particularly seem to be wet with fuel and your exhaust smell was more egg than fuel. I would first check the engine temp sensor by unplugging it and seeing if it will start. Also as mentioned before fuel filter could be blocked or the fuel pressure regulator could have failed causing low fuel pressure but that's unlikely. Injectors might be clogged up, have you tried a squirt of easy start? The 3rd gen prelude was never fitted with a catalytic converter in the UK so that can be eliminated from the diagnosis. Try the temp sensor first, if not try a squirt of hope and see what happens.

[arif_manji]

Before just changing the cap (which almost certainly is worth doing) have you checked you do actually still have spark? Check that first to rule it out, so you know your 'starting point' for the fault.

One other possibility that does match the symptoms, is the timing jumped - but that's pretty drastic and hopefully you don't have that. Have you had the cambelt done yet?

Hi Iain,

It's definitely getting sparks. I'm not sure about the cambelt as it came with no history unfortunately.

[arif_manji]

I've never once had a prelude hunt at idle, the closest thing to a hunting idle in my experience was when the new timing belt was a tooth out but this was sorted by the garage doing the work at the time. Also if the idle control valve needs cleaning it can cause cold running issues but should still start ok and goes away when warmed up. Once you have checked ignition and are confident it's got a healthy spark next check the fuel pump is definitely running and it's not a main relay fault (hot start issues as you described and plenty of info online to check) crack open the fuel line on the fuel filter and turn on the ignition briefly to see if there is good pressure. If all is good with spark and fuel next check the engine temp sensor has not failed on the PGM-FI. It could be reading hot when it's cold and vice versa giving the ECU a false reading which will give cold start issues because the fuel map won't compensate for the extra fuel needed in cold start conditions and hot start issues if it thinks it's cold when it's hot. Not to be confused with temp gauge sensor as I'm pretty sure it has 2 sensors one for ECU and one for temp gauge.

There is an old saying in Rover V8 circles "most fuel problems are ignition based and most ignition problems are fuel based" or something along them lines anyway. I think the point was that symptoms often lead us to dead ends. Backfiring if it's not a timing issue is usually down to lean running conditions and as you said the plugs didn't particularly seem to be wet with fuel and your exhaust smell was more egg than fuel. I would first check the engine temp sensor by unplugging it and seeing if it will start. Also as mentioned before fuel filter could be blocked or the fuel pressure regulator could have failed causing low fuel pressure but that's unlikely. Injectors might be clogged up, have you tried a squirt of easy start? The 3rd gen prelude was never fitted with a catalytic converter in the UK so that can be eliminated from the diagnosis. Try the temp sensor first, if not try a squirt of hope and see what happens.

The hunting starts as soon as the engine get a little up to temperature. On the 4th Gen, sometimes the fix for this is to open up the coolant bleeding valve but on this 3rd Gen, nothing is coming out? I'm starting to thing the thermostat might be stuck? The radiator and reservoir bottle have brand new coolant (I replaced including oil before starting it up for the first time).

As @Scott560 mentioned regarding the distributor cap, I think this is the cause. I left it for a couple of days and it started up within the first short crank without any backfire! I have ordered a new cap and rotor arm as I think this could be the cause. Also a new thermostat which hopefully fix the hunting issues.

If this doesn't fix the issue, ill investigate what you have suggested.