Wont start on the key, WILL bump start...

[Braymond 4]

I wonder if anyone can suggest the next thing to check...

 

I thought in these cold months the battery was tired and not holding quite enough charge to start, though it was turning over fairly happy - just not starting. So i changed the battery, and it started. Once. Then back to bump starting again (which works fine 100% of the time)

 

I then realised I didn't hear the fuel pump prime so research suggested the fuel pump relay. I bought one from Miles' eBay shop, swapped it over this afternoon...still nothing.

 

Still turns over perfectly keenly, just never fires. Whats the next thing to check???

[jackherer 543]

It could be the starter even if it turns over OK. They can develop a fault that means they generate a lot of electrical noise and prevent the engine management from syncing to the pulse from the crank or dizzy (depending on model)

 

It's a pretty obscure problem so rule other stuff out first (electrical connections, grounds, battery terminals etc.)

 

 

What year is your 205? And what engine management? Jetronic or Motronic?

 

It wont be the battery if it turns over, a 205 running either Jetronic or Motronic will just about catch and fire up even if the engine is turning pretty slowly.

[Braymond 4]

9 minutes ago, jackherer said:

It could be the starter even if it turns over OK. They can develop a fault that means they generate a lot of electrical noise and prevent the engine management from syncing to the pulse from the crank or dizzy (depending on model)

 

It's a pretty obscure problem so rule other stuff out first (electrical connections, grounds, battery terminals etc.)

 

 

What year is your 205? And what engine management? Jetronic or Motronic?

 

It wont be the battery if it turns over, a 205 running either Jetronic or Motronic will just about catch and fire up even if the engine is turning pretty slowly.

Its an '88 - phase1.5. I don't know whether that's jetronic or motronic though. 

Grounds and terminals are sound.

[Braymond 4]

Other than a relay, what else might prevent the fuel pump priming?

[jackherer 543]

That'll be Jetronic.

 

The pump priming on a Jetronic 205 is triggered by the tachymetric relay when it receives the same trigger that goes to the starter solenoid. It's a while since I've had a Jetronic 205 but my memory is that the priming is pretty hit and miss, some relays just don't do it but it doesn't really cause many issues, it just means it takes a few more cranks to start if it's been left for a while.

[steve@cornwall 100]

Same as any non start, surely the first port of call is to ascertain if it has spark and fuel? 

Maybe theres a fault in the starter causing it to draw too much current and not leaving sufficient reserve for spark, or a ground issue thats not allowing the injectors to open, but when bump started the inertia closes a broken wire etc etc. 

I believe the fuel pump has no need to prime if the fuel system is already pressurised? 

Reminds me of my old bedford cf, they have a shunt that diverts power straight from battery to ignition whilst cranking. If that goes belly-up it will not start on the key but bump starts perfectly.. 

 

[jackherer 543]

34 minutes ago, steve@cornwall said:

Reminds me of my old bedford cf, they have a shunt that diverts power straight from battery to ignition whilst cranking. If that goes belly-up it will not start on the key but bump starts perfectly.. 

 

I thought that sounded familiar

 

In my experience Jetronic 205s will fire with an almost flat battery that can barely turn the engine over so I'd be surprised if the starter is drawing so much current the coil can't fire.

 

36 minutes ago, steve@cornwall said:

I believe the fuel pump has no need to prime if the fuel system is already pressurised? 

There is no fuel pressure sensor so the tachy relay has no clue if there is pressure or not.

[DamirGTI 342]

I've found that priming depends mainly on the make/brand of the tachy relay fitted , so the system primes with ignition ON with certain brands of relay and with others it does not . But makes no difference if it primes or not really .

 

If it's not the starter motor issue as Kieran says , i'd also have a good look at the power and ground wires from the battery to the starter and battery to the grounds .. also battery terminals +/- ... for oxidized power-and-earth wiring under the insulation , oxidized battery terminals , grounds and positive connections .

 

Also , try to wiggle/twist a bit the dizzy signal cable while cranking .. and open up the yellow 3pin connector which connects dizzy pick up coil with the ignition amp , inspect and clean contact terminals .

 

Thinking back in the days i was called out by a few local people to help starting up some 205/309's , which also did start up by pushing ("bump start") and the starter was spinning fine on them ... but they simply didn't want to start via key , there was a spark and fuel , but the spark was mostly weak .

If i remember most of them had old Ducellier ignition amps , when i tried test replace those with blue Bosch amp - they fired up instantly on the first turn of the key .

 

Certain types of the spark plugs are also notorious for creating no start problem , even if there's spark while testing them out of the cylinders , something obviously happens while they're screwed inside the cylinder in the prescience of pressure vacuum etc. and they simply don't want to start/ignite the mixture .

Had this on a Rallye 1.3 TU24 with brand new twin electrode NGK plugs - no start (started up on the first turn of the key with old Eyquem single electrode plugs after few hours of scratching my head wtf ?!) , and some other non PSA cars seems to dislike certain spark plugs with regards to starting up ... 

 

Another thing i usually suggest trying out in such cases is , some "easy start" spray for diagnostic purpose or to aid starting up cars which where left standing for longer periods unused ... can help to start it up initially , then after good blast when everything in the engine bay heats up and dries off moisture it's usually fine afterwards to start up as it should .

 

Use easy start spray for testing purpose :

 

- if it starts and runs on spray then there's spark but no fuel

- if it doesn't run on spray (not even a cough) , usually no spark (or weak spark) , or can be both no spark and no fuel (to divide that further : take the plugs out and see if they're wet .. if so then there's fuel , so lacks just the spark or the spark is too weak to ignite) 

 

 

D

 

Edited February 15, 2020 by DamirGTI

[Braymond 4]

Really helpful posts - thanks very much!!

Just need it stop raining now...

[Tom Fenton 1,542]

Interesting one. I think I’d check for spark when cranking. The distributor supplies the cranking and speed signal to both the ignition and ECU for the injection. The sensor I think is VR and if it’s gone weak perhaps isn’t giving enough of a signal at cranking speed, but at bump start speed and above perhaps is good enough.

[SRDT 175]

Ignitors can have a sensor but on a Bosch unit it's a big pulse generator:

You can check the coil (3) and the cable (4). I don't have the specific value for the GTI ignitor but the coil should be around 990-1210 Ω.

 

[Braymond 4]

I've finally persuaded the wife to come out and turn the car over while I check for a spark. What can I earth the plug threads to?? Everything in reach seems to be ally 

 

Edit: if that isn't actually an issue, and using the manifold is good enough then I have zero spark on any plug, with a new dizzy & coil...

Edited April 19, 2020 by Braymond

[jackherer 543]

Earthing to the inlet manifold is fine. The cylinder head, engine block and the gearbox casing where the main ground is bolted are all aluminium anyway.

 

Check the distributor signal cable and the ignition amplifier if the coil and distributor cap are new.

[Braymond 4]

3 hours ago, jackherer said:

Earthing to the inlet manifold is fine. The cylinder head, engine block and the gearbox casing where the main ground is bolted are all aluminium anyway.

 

Check the distributor signal cable and the ignition amplifier if the coil and distributor cap are new.

Where is the ignition amplifier? 

[DamirGTI 342]

On the left inner wing , just beneath the strut top .. or can be in the same position but on the right inner wing , on later models .

 

It's (and must be) bolted on the ally plate , small square box .. blue , gray or black depending on module age and brand .

 

D

[Braymond 4]

Thank you!

[jackherer 543]

Damir's photo also shows the distributor signal wire which has the yellow plug. Follow that wire back to the distributor body which is where they often fail.

[DamirGTI 342]

"Stolen" photo from the web !

But serves the helping purpose .

 

Agreed about the signal cable , very important thing to check too .

 

D

 

 

[Sumpguard 2]

When you say new dizzy not a mapco one buy any chance ?. I had starting problems after  fitting a new distributor put the old Bosch one on started as soon as I turned the key.