Hot Start Issue

[Hanaldo]

No... Probably a good idea, I'll give that a go.

[Hanaldo]

Bit of an update with this. Last night me and my dad had a look at a couple of things to see if we could figure out the most likely cause. Most of the stuff we tried didn't change anything, but two things we tried had interesting results.

Firstly, we measured the voltage drop between the battery and the power line going to the fuse box in the engine bay while cranking. It first drops down to about 9.5v and then goes back up to 10v before finally getting up to 10.5v when the engine catches and I stop turning the key. I mentioned to him about the injectors requiring enough voltage to be able to open, but we were both pretty sure that this must be enough voltage for them to open? Even if 9.5v was too low, surely 10v wouldn't be too low and they should be opening? Or do the injectors require such a high voltage?

The second thing we tried was an attempt to identify whether it was the batteries location in the boot that was causing the trouble. We left my battery where it was in the boot, and used jumper leads to connect the battery in my dad's car to the fuse box power supply. This definitely helped. With the battery connected up there, it no longer cranked for ages without firing. The thing is, it still wasn't perfect. It would still crank for awhile, and then it would sound like it had fired so I would stop turning the key and it would just die. It took a few attempts at cranking to get it to fire, but it would eventually start every single time. With my dad's battery disconnected again, it would go back to cranking for ages without firing.

In summary, it does start better with a battery supplying power to the fuse box, but it still isn't good. If I were to patch a battery into the front again, I would still say it has a hot start problem. So, anyone have any ideas about what we have discovered here?

[bubba]

Well seeing as the issue only started after you relocated the battery to the boot, and patch in another battery at the fuse box seemed to help the issue.. I am still thinking it's a major voltage drop due to the battery location, or poor wiring/bad earth etc.

[Hanaldo]

Well seeing as the issue only started after you relocated the battery to the boot, and patch in another battery at the fuse box seemed to help the issue.. I am still thinking it's a major voltage drop due to the battery location, or poor wiring/bad earth etc.

The fuse box is seeing 10v though. It's a bit low, but it's enough to spin the starter motor, so surely it should be enough for everything else? And how does it relate to heat? Surely if the problem were low amperage or volt drop then it would still give trouble when cold? Why does it only give trouble when hot? Also, the relocation simply made things worse, I did have trouble hot starting before I moved the battery. So could there be something that is heat related and made worse by having a lower voltage?

I'll quadruple check the earth points and wiring. Another thought I had... My fuel pump is directly wired to my battery. Could there be something heat related that causes the fuel pump to not get enough voltage? It does prime before cranking though. I'll check I'm getting fuel to the rail when I get home today.

Edited September 13, 2011 by Hanaldo

[bubba]

Doesn't heat increase resistance? There could also be a connection that becomes dodgy once things heat up and expand.

When you say the fuel pump is directly wired to the battery, is that 12v from the fusebox? or straight from the battery in the boot?

[Hanaldo]

Straight to the battery in the boot...

[bubba]

Obviously via a relay, tried another relay?

[Hanaldo]

No.

I'll check if I'm getting fuel to the rail first. If I'm not then I'll try a new relay.

[Hanaldo]

Bit of a strange update with this, it's sort of just... gone away

Haven't had any trouble for about a week now. Still not starting perfectly, but it's back to how it was before I relocated the battery. I haven't fiddled with anything since I tried patching a battery in at the front, so no idea what's going on. Knowing my car, it's going to come back when I least expect it

[bubba]

Ahhhh electrical gremlins!

[Room42]

I was reading about stuff and I came across this.

This non-return valve must not be removed from the fuel pump, removal will result in fuel system pressure loss as soon as the fuel pump is shut down. If the fuel system cannot retain a certain amount of pressure after shutdown, fuel vapourisation may occur in the fuel lines and rail resulting in difficult hot start characteristics.

http://www.bosch.com.au/content/language1/html/4716.htm

Maybe your pump and mine are a bit worn out? I swapped my fuel pump at the same time as my injectors so it is possible that it has been the fuel pump the whole time.

[Hanaldo]

Ok forgot to update, I actually managed to fix this issue before Powercruise last weekend. It turned out to be the earth cable from the block to the chassis, the cable was farked. The workshop that did my engine swap used the oldest, dodgiest piece of wire I have ever seen, it was so corroded and fraying apart I'm surprised my car ran at all. Had the worst crimp onto the eyelet, I didn't even pull it hard and it came out. Then they just wrapped it in tape and put some conduit around it, it looked like a brand new wire. Fkn Perth workshops, there just doesn't seem to be a good one around, why does nobody take pride in their work these days?

Anyway, have replaced the cable with some nice brand new high amperage stuff, haven't had a problem since

[Room42]

Ok forgot to update, I actually managed to fix this issue before Powercruise last weekend. It turned out to be the earth cable from the block to the chassis, the cable was farked. The workshop that did my engine swap used the oldest, dodgiest piece of wire I have ever seen, it was so corroded and fraying apart I'm surprised my car ran at all. Had the worst crimp onto the eyelet, I didn't even pull it hard and it came out. Then they just wrapped it in tape and put some conduit around it, it looked like a brand new wire. Fkn Perth workshops, there just doesn't seem to be a good one around, why does nobody take pride in their work these days?

Anyway, have replaced the cable with some nice brand new high amperage stuff, haven't had a problem since

Man that's good to hear. My earth strap is broken too. I was too lazy to fix it. You should go back to the shop that did the engine and tell them all the trouble you've had with it.

[Hanaldo]

Man that's good to hear. My earth strap is broken too. I was too lazy to fix it. You should go back to the shop that did the engine and tell them all the trouble you've had with it.

Yeh they seriously couldn't care less hey. My mate had his engine built there, 30k engine build and then they filled the gearbox with water instead of oil, and used silicon to seal the sump. Needless to say it didn't last long and they didn't wanna hear about it when he complained. They also charged someone I know 8k (not including the motor) to install a bog-stock SR20 into an S13, then did the worst job I have ever seen. My mate and myself ripped it out and did it again, did a way better job than they did. They also charged the poor girl 1.5k to install a 'heavy-duty' clutch, but she found it was slipping so we pulled it off and sure enough it was a worn out stock replacement item, looked like it had been ridden hard for a long time. No way it was new, and it certainly wasn't heavy duty.

They also did this:

Looks pretty secure

Edited October 9, 2011 by Hanaldo

[zebra]

HAHAHAH

Care to pm me the Workshop?

[Room42]

Yeh they seriously couldn't care less hey. My mate had his engine built there, 30k engine build and then they filled the gearbox with water instead of oil, and used silicon to seal the sump. Needless to say it didn't last long and they didn't wanna hear about it when he complained. They also charged someone I know 8k (not including the motor) to install a bog-stock SR20 into an S13, then did the worst job I have ever seen. My mate and myself ripped it out and did it again, did a way better job than they did. They also charged the poor girl 1.5k to install a 'heavy-duty' clutch, but she found it was slipping so we pulled it off and sure enough it was a worn out stock replacement item, looked like it had been ridden hard for a long time. No way it was new, and it certainly wasn't heavy duty.

They also did this:

Looks pretty secure

What pricks.

[bubba]

That is a new height of dodginess! and the reason why I do all this stuff myself

[Hanaldo]

That is a new height of dodginess! and the reason why I do all this stuff myself

Yeh, I do everything I have the tools and know-how to do myself. Back when I did my engine swap, I knew bugger all about how to do an engine swap or anything like that. Now I've done two If I knew what I know now, I would easily have done it all myself.

[bubba]

Hindsight is always 20/20

Glad you got it sorted anyway mate, now you can just enjoy teh beast