6v at fuel pump???

[Kitch]

Valver won\'t start. It\'s been sat around for a year and normally starts first time every couple of months but recently has been struggling to get going, needing 30secs or so of cranking before coughing into life. It\'s almost like it\'s ran out of fuel and has just been topped up again, and you\'re egging on the fresh stuff up the pipe!

I have a spark, fuel on the plugs and I\'m pretty sure air is in there somewhere too! Today I changed the fuel pressure regulator and vacuum hose as that was my bet. No dice.

I downloaded the PDF and set about checking the ECU pins for continuity and resistance. All good on the ECU. The good Doc suggested the Ign relay may be at fault, and he\'s not far off....I think it might be the fuel pump relay. It\'s only dishing out 8-9volts at the relay when cranking, but is recieving 12v when stationary. The pump is only recieving 7-8volts, so it is working but obviously not enough to create the pressure needed for the injectors to fire properly.
I\'ve changed the fuel pump relay with an old 4-pin wiper one I had laying around, but the behaviour doesn\'t change at all. I can feel it clicking in my hand though, just like the original relay.

Looking at the wiring diagram, I think I\'m right in thinking that the feed comes from the ign switch, then into the relay which then feeds the pump when the engine is cranking or running only? Is that right? Because if it is, it suggests a dodgey relay, but I\'ve already changed it (for 3 different ones, I have a hoard!)

So that\'s where I\'m stumped. Any ideas?


Chiz

[mat_fenwick]

As far as I can remember you're right in your FP relay logic.

So the output of the relay is 8-9V when cranking, and the input is 12V when not cranking. Obvious question time - what is the relay input voltage and battery voltage when cranking? Need to work out where the voltage drop is occurring...
Have you tried temporarily running a 12V feed to the FP to prove your theory? I had exactly the same problem with an Alfa 75 I was running a few years ago - I was getting voltage drop somewhere in the loom. I ended up running a bypass wire as I never found where the drop was. It happened just after overtaking a stream of cars and a coach, which was very embarrassing having to coast to a halt and wait for everyone I'd just overtaken to try and squeeze past me again!

[Kitch]

Good point, I\'ll check the input voltage when cranking tomorrow. It was obvious, but sadly for me not obvious enough

I didn\'t get round to hooking a 12v source up to the pump as I didn\'t have a battery to hand, or wires long enough! I\'m pretty confident it\'ll work fine with the 12v feed at this stage though.

Thing is apart from 20 year old French wiring, what can cause the voltage drop? I don\'t think I\'ve got any mice living in it and it hasn\'t really been touched in over 18months, just started and moved a few yards every couple of months when I needed to get something at the back of the garage!

[mat_fenwick]

Any connections in the loom would be the place to start, is there anywhere that shows evidence of getting hot? (From the voltage drop dissipating heat?)

But if your battery voltage is dropping to 8-9V when cranking then this ain't your problem! The problem I had in the Alfa was actually slightly different TBH, in that the voltage was not enough to even get the FP to run at all. I didn't do any measuring, as I just had to guess and bodge it (quickly!) at the side of the road.

[Kitch]

Went through of them earlier but not all the little ones. Need to test the battery and input for voltage drop then really don\'t I?

On the 16v forum, theres a fantastic download for the Cap system for ML4.1 engines. It\'s got all the info needed, so just going through that at the mo.

[electrokid]

Battery voltage dropping to around 9v is quite normal during cranking - 8v is a bit low. If fuel has flowed back to the tank while the car has been standing and you might have air in the system then you're doing more cranking before fuel actually gets to the engine that will lower the battery voltage further. And the battery will not like standing uncharged - you could try starting it once a week instead.

[Kitch]

There is fuel getting through to the rail, but it\'s just at a low pressure and I think it\'s too low for the injectors to fire properly.

I don\'t start it weekly as I don\'t want to just start it and leave it idling as we know that\'s not good for an engine, and it\'s not taxed/tested/insured so driving it is risky. Anyway I\'d rather have the battery die than coke the head up, but to be honest the battery is normally plugged into a trickle charger, so it never goes totally dead. It always seems to have plenty of oomph. Even after 5mins of cranking, it didn\'t sound like giving up. I think it\'ll burn a lead out before that happens

But you\'re saying roughly 9volts at the pump during cranking is normal?

[electrokid]

9v is normally quoted as being the minimum voltage to expect from a battery in decent condition - at the battery terminals. Any equipment running will also suffer from voltage drop along the wiring and across connectors as usual. If I had a normal sized battery and it went down to 9v during cranking I'd consider that to be on the poor side of normal - and a 1v drop between the battery and the fuel pump sounds reasonable too.

Put a DMM directly on the battery while cranking - if it's lower than 9v then the battery could be suffering. With the engine running measure the battery volts then the volts on the fuel pump itself - I'd expect a volt or so difference between the 2 readings to be normal.

If the cranking volts are >9v and the drop to the pump is <2v then I'd think the problem to be elsewhere. If the car has stood in high temperatures at any time during the year then the lower fractions in the fuel may have evaporated over time which will make starting harder - moisture may have got into the fuel - try putting some fresh fuel in or if you suspect moisture then Holts 'dry fuel'. Connections to the ignition amp may have oxidised slightly making the connection poor or intermittant. Any moisture in the bores may have soaked into the ceramic insulators of the spark plugs. I'm sure they may be a dozen other possibilities.

[Way2go]

The pump is only recieving 7-8volts, so it is working but obviously not enough to create the pressure needed for the injectors to fire properly.

You will likely have sufficient pressure in the rail as the pump will run continuously with the ign switch in the start position and overpressure is returned to the tank anyway. I would wonder if the injectors have gummed up during lay-up? But you say the plugs are wet?

Can you see the injectors on the rail on a 16v like an 8v? What I have done as a test faced with fuel problem is, remove the rail and the injectors, reassemble the injectors on the rail with the assembly above the apertures so I can see the base of the injector and then observe that all injectors spray when trying to start.

I would recommend having a fire extinguisher readily to hand just in case but happily I didn't need one and it did identify the problem.

[Kitch]

[quote=\\"Way2go\\"][quote=\\"Kitch\\"]The pump is only recieving 7-8volts, so it is working but obviously not enough to create the pressure needed for the injectors to fire properly.[/quote]

You will likely have sufficient pressure in the rail as the pump will run continuously with the ign switch in the start position and overpressure is returned to the tank anyway. I would wonder if the injectors have gummed up during lay-up? But you say the plugs are wet?

Can you see the injectors on the rail on a 16v like an 8v? What I have done as a test faced with fuel problem is, remove the rail and the injectors, reassemble the injectors on the rail with the assembly above the apertures so I can see the base of the injector and then observe that all injectors spray when trying to start.

I would recommend having a fire extinguisher readily to hand just in case but happily I didn\\\\\\\'t need one and it did identify the problem. [/quote]

I wondered when you\\\'d mention injectors :p

They\\\'re fine, I\\\'ve changed them, the rail and the FPR for units I know were fine too. When cranking over with the plugs out, the you see the fuel vapour being shot out the top of the bores (though I\'m not totally sure if it\'s the correct amount). I\\\'m pretty sure they\\\'re firing but I\\\'m not sure that it\\\'s either at the right times, or if they\\\'re fire enough to actually get a bang.....ie they\\\'re spraying a small amount (enough to wet a plug) which is just burning up and not actually sustaining long enough to be compressed and ignited. The pump is running, but I suspect not enough to create the 3bar or whatever it is.

FWIW I tried bypassing the relay completely tonight, so the pump comes on with the ignition in the \\\'M\\\' position. Pump fires up fine, and fuel being pumped....but still won\\\'t start. It\\\'s almost trying to....you know when you\\\'re cranking and the starter starts hopping slightly as the engine tries to catch? It\\\'s like that.

Like I said, best description is that it feels like it\\\'s about to run out of fuel and you\\\'re trying to start it with air in the pipe, if that makes sense?

I think next step is to hook 12v up to the pump directly and see if that goes. It really should, all things considered. Then I think I\\\'ve probably got a wiring fault somewhere. The battery is now on a proper drop-charge just in case and prior to that was up to 12.7v with the trickle charger, which was the same reading using either the engine or the body as the earth, so I don\\\'t think it\\\'s an earth fault. It\\\'s got 2 more earth straps than is standard anyway, to give the electrics a boost.

So......anybody lost yet?

[mat_fenwick]

So......anybody lost yet?

Yes...those sodding backslashes really screw up your quotes!

No suggestions I'm afraid, but we'll know more when you put 12V across the fuel pump.

[Kitch]

Don\'t get me started on the backslashes. I hate fucking computers!

I will put 12v across it and see if I can get her going. It\'s totally baffled me, especially as it was running fine not a week ago.

[Kitch]

Erm....right. Things have changed slightly! I\'ll copy my BX 16v thread across:

Well just to totally spin things around......the pump is fine! I re-charged the battery fully last night (the one that flattens it, then recharges it)
Now I have 13.4v between the terminals of the battery, rather than 12.2v ish. The car still spins over, just a bit quicker. But crucially there is now 10.8v at the pump (with the pump running).
I think this pump thing has been a bit of a red herring. For all I know the car might well normally start with only 8v at the pump, I\'ve never checked before. But because I\'ve been and crawled under it, I\'ve been taken in and it may well have masked a different problem.

Still won\'t start! Relay by-passed or not. I borrowed a fuel pressure tester from work and it blew the end off! Petrol in eyes burns, fact!

So....I have fuel in the rail at high pressure, and the plugs are wet with fuel when I remove them. The plugs are sparking if I remove them and hold them against the engine while cranking. Nice thick blue sparks. Cam timing is also fine.
But still no start up!

I\'ve been told of a theory however, which says that a spark plug mounted in the head attempting to spark under compression will have more trouble than one in the open, such as when I remove them to test for a spark. Something to do with air volume? So I wondered if it\'s possible my problem is in fact ignition related, not fuel. If I have a weaker spark than what at first appears, it may be sparking outside the head, but not once fitted. I don\'t have any plug lead testers, but may be able to get hold of some tomorrow (thinking about it, will these show if the plugs are sparking, or just if the leads are taking the charge?)

There is still always the possibility that my injectors aren\'t firing at the right times. Guess the ECU controls that?

Now the coil is only about 18months old and has only covered around 2k miles, but I checked the resistance across pins 2 & 3 and got 1.2ohms, when apparently I should have been getting 0.8ohms. Checked 2 & 4....nothing. Should have been 6500ohms! Now I\'m not sure exactly how a coil works, but I\'m guessing that\'s not right. I couldn\'t find the resistance figures for the ign amp to test that sadly.

The only pin test on the ECU plug that has so far failed is the coolant temp sensor one, which refuses to register anything. Seems odd, but even with this unplugged the car still ran!

So tomorrow I\'ll see if I can get a HT lead/plug tester, maybe even order a coil if I can find one cheap enough!

[mat_fenwick]

I've been told of a theory however, which says that a spark plug mounted in the head attempting to spark under compression will have more trouble than one in the open, such as when I remove them to test for a spark. Something to do with air volume?

Yes - it's when it's under compression the spark finds it harder to jump the gap. Do you have a timing strobe light? As you can clip the pick up of that to your plug lead(s) and if there is no spark the strobe won't fire.

I had that on the Disco where the (new) HT king lead failed - spark was fine in air, but not in the cylinders (and the last thing I suspected was the 2 month old HT leads!)

EDIT - Is your meter set to the right range for 6.5 kohms? It would seem strange for there to be a break when testing with a meter yet be able to generate a spark at all! It's not unknown for them to be OK with a meter but the insulation break down under high voltage.

Does the rev counter behave any differently to normal while cranking?

If you get someone to crank it over when it's dark, you may be able to see HT tracking finding its way to earth, IF that is the problem.

[Kitch]

I don\'t have a strobe, but I bet the place I just started working does!

Meter was set to right range, yeah. It\'s got 200, 2k, 20k, 200k and 2000k IIRC.

Rev counter lifts up very slightly, possibly 1-2mm at most. Doesn\'t bounce.

Just got Nat to crank it over in the pitch black outside....no arcing anywhere that I can see.

I think it\'s losing a spark now, but check out what I just found on 205 drivers:

http://forum.205gtidrivers.com/index.ph ... 23111&st=0

Pretty interesting stuff, no?