Low voltage at pump, suspected aftermarket alarm

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Low voltage at pump, suspected aftermarket alarm

by Martin.p » Tue Mar 24, 2015 11:45 pm

Hi, The calibra has not been running quite right. I found I'm only getting 9v at the pump.
I cleaned and checked the earth lead. But the live runs through a aftermarket alarm.
To start car I have to turn ignition on then press a button on the fob befor the pump runs. Then turn key again to start. It's a GT 136 (if that means anything to anyone)

Can I bypass the alarm with new wire from ECU to pump? So I can workout if it's to blame?

I don't really want the alarm on the car, but I don't want to go to the hassle of cutting it all out if it dosnt help the pump voltage?

Or could something else be causing the voltage drop? Like fuel pump relay?
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Re: Low voltage at pump, suspected aftermarket alarm

by Martin.p » Wed Mar 25, 2015 7:23 pm

Update. I've ran a wire from the negative strait from battery to pump and still get 9v so I ran a wire from the plug down nr ECU (red/blue trace) strait to the pump and now it's cut out the need for fob and starts as engine cranks. And I'm getting 10v at pump. But unsure if the alarm is still interfering with circuit somehow. Also changed fuel pump relay with no change to anything.
I'm really unsure about electrics could really do with some help here :(
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Re: Low voltage at pump, suspected aftermarket alarm

by Martin.p » Wed Mar 25, 2015 7:48 pm

I total appreciate it's hard to do over the Internet.

The wire I used was slightly thicker than the standard wire.
I've got a multimeter I borrown off my dad. Sadly I'm not 100% sure how to use it but got setting on where it measured 12.5v across the battery.
I've been checking the voltage at the pump while the car is running at the two terminals on the pum under car.
I've not checked the battery voltage while the car is running.
And yes it looks like the fuel pump feed goes through the alarm. supported by the fact of when I joined to feed nr ECU I didn't need the fob to get the pump to run as befor. But it started when I turned the key to crank.
I've refrained from undoing all the tape where the alarm has been spliced in atm. But feel I'm going to have to cut it all out so I have a fresh start :(
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Re: Low voltage at pump, suspected aftermarket alarm

by Martin.p » Wed Mar 25, 2015 7:56 pm

If it makes any diffrence the engine and loom and ECU all came from a cav GSI where the fuel pump relay is in the fuse box in bay and not by ECU behind kick panel
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Re: Low voltage at pump, suspected aftermarket alarm

by Martin.p » Wed Mar 25, 2015 8:18 pm

I'm pretty sure the earth is ok (arm) because I ran removed the earth from pump and ran the new wire from pump the negative directly to battey so not to use body as the earth.

But I'll check battry voltage while engine is running, as I haven't yet

I've only tried the pump with either one or other attaced (as in live or negative)

I'll also try testing at fuse at 11.
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Re: Low voltage at pump, suspected aftermarket alarm

by Martin.p » Wed Mar 25, 2015 8:22 pm

I have little or no knolage of electrics on cars. I'd happily pull pistons out.
Should the fact I'm measuring the voltage at pump with it attached make any diffrence? Will it measure voltage drop across the pump?
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Re: Low voltage at pump, suspected aftermarket alarm

by Martin.p » Wed Mar 25, 2015 8:32 pm

I haven't tested it yet, but let's say the voltage across the battery was lower then 12v when the car is running would that point towards the alternator not generating Enough power?

Reason I ask is because if I turn lights on and cabin fan the battery light on dash lights up (very dim) and if I use heated seats it gets brighter!

Pointing towards failing alternator!? Yes/no
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Re: Low voltage at pump, suspected aftermarket alarm

by Martin.p » Thu Mar 26, 2015 10:17 pm

Ok, I checked the voltage across the battery
12.5v without car running
12.9v with car running

Then I removed the wires from the pump! and checked voltage!
And it read 12.3v
So the 9v I got befor when wires where still attached to pump must of been reading the voltage drop across the pump.

So low voltage at the pump is not the issue with its running.
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Re: Low voltage at pump, suspected aftermarket alarm

by Martin.p » Fri Mar 27, 2015 9:52 am

The car is up on ramps and I just pulled back the rubber sleves over the pump terminals and touched the multi meter on the terminals.

Yes I checked fuse 11. I pulled the it out and it had no voltage at all and the car still ran with it pulled out!?
11 is the one on middle row and the first one on left side. Labeled FI on the discription panel.

There is a fues that's been fitted between the alarm unit and the loom. Guess someone has by passed the main fuse

Didn't realise I was meant to be getting 14v with engine running :/
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Re: Low voltage at pump, suspected aftermarket alarm

by DanSE4 » Fri Mar 27, 2015 10:55 am

Martin.p wrote:Didn't realise I was meant to be getting 14v with engine running :/


12.9v with the car running is very low, should be around 14v - 14.5v. The voltage you're seeing could very well point to a failing alternator or just a very weak battery, I'd check that battery in another car & see what voltage it's showing while running in that, if you're seeing 14v odd in another car that I'd be inclined to think probable alternator failure.

Weak batteries/failing alternators can cause all sorts of electrical issues by supplying weak voltage & amps so given the reading you've got from it, I'd get that sorted as first port of call just to rule that out as a possible cause.
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Re: Low voltage at pump, suspected aftermarket alarm

by Martin.p » Fri Mar 27, 2015 12:06 pm

I'll check battery in diffrent car later.

Going right back
The car bacicly idles badly and sometimes stalls . And when I pull away it bogs down. But drives until you put your foot down, then it splutters! But will drive right up to a good speed as long as I push it away slowly.
So I bought
New leads
New plugs
Then off my nova (let) which runs fine
The distributer cap
Rotor arm
Dizzy body
Fuel pressure reg
Lamba sensor
ICV
Fuel pump
Fuel pump relay
Until last night I was sure I fitted new CTS befor I fitted engine.
But spotted it's got a old one.
So orderd a new one today.
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Re: Low voltage at pump, suspected aftermarket alarm

by Martin.p » Fri Mar 27, 2015 12:12 pm

I'm concerned the alarm runs deep. I'd like it removed but once I start there's no going back. Rather see it working . If at all possible first. Trying to leave removing it till last resort.

I'll aslo try getting a fuel pressure tester somhow.
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Re: Low voltage at pump, suspected aftermarket alarm

by Callyman » Fri Mar 27, 2015 1:52 pm

Try MAF sensor
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Re: Low voltage at pump, suspected aftermarket alarm

by Martin.p » Fri Mar 27, 2015 2:03 pm

Had questioned it. But I don't have a spare one of them. And the one on the LET looks the same but has a diffrent part number.
I had also thought about injectors. But again the let ones are yellow.
Plus all 4 plugs are same colour (unless all 4 are failing by the same amount. Which I doubt)

If it was MAF sensor how would/should it react? Because I can 'hold' all speeds at all revs and car runs solid. It's only when you demand power. Like pulling away and hard (ish) acceleration.
My first thoughts where plugs and leads and ignition parts. As it feels like weak firing. But after changing all the above I started looking at fueling. And changing all them parts.

Compression tested it also and there all 190-200 with no two the same side by side.
I have also got a oil leak from rocker cover or front cam seal. That I just can't seem to seal up.
Atm I'm putting it down to high oil pressure. Need to check my oil release valve. (No oil gauge in car)
But I don't think the two problems are connected!?!
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Re: Low voltage at pump, suspected aftermarket alarm

by DanSE4 » Fri Mar 27, 2015 2:17 pm

Martin.p wrote:The car bacicly idles badly and sometimes stalls . And when I pull away it bogs down. But drives until you put your foot down, then it splutters! But will drive right up to a good speed as long as I push it away slowly.


I had very similar in my old Cav SRi XE, sold it as it was & the buyer found that the new alternator had been poorly connected (not fitted by me - car mechanics were quite foreign to me back then) which he told me once fixed cured the running issues. If you've ever driven a car with a charged battery but knackered alternator, you'll know the mayhem that happens when the battery reaches it's last bit of juice for a minute or two before the car finally dies!

So, I'd still be resolving why you're only getting 12.9v across the battery terminals with the engine running before looking at anything else. Not saying that is the cause of everything but if you're trying to troubleshoot electrical issues when you have an obvious one there already, you'll could be chasing your tail until that gets sorted.
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