Help needed please - fuel issues and starting problems

Help needed please - fuel issues and starting problems

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Discussion

mach2

Original Poster:

226 posts

233 months

Friday 24th March 2017
quotequote all
Gents,
Help required please.

So the car has been laid up over the winter while I've done a few refurb jobs on the suspension, etc.
Battery was disconnected and was on trickle charge throughout.

Go to start the car earlier but it won't start up.
Check the spark at the plugs and all 8 are good. Check the plugs and they are dry, no fuel getting into the bores.
Fuel pump is priming and providing fuel to the rail, checked this by removing the fuel feed at the rail and there is a plentiful supply of fuel coming through. However there is no fuel coming to the return side of the rail and when depressing the vent on the fuel rail nothing is coming out.
I'm at a loss as to why no fuel is getting to the bores when it's at the rail or why there is nothing in the return feed.
Have checked fuses, relays, etc but all are working.
What am I missing? All advice greatly appreciated.
Thanks guys

ianwayne

6,243 posts

267 months

Friday 24th March 2017
quotequote all
Sounds like you may have a blockage in the fuel rail.

If you press the little schrader valve on the o/s of the fuel rail after initial ignition on, do you get a spurt of fuel out? If so, you have fuel pressure in the rail. Unless that is what you meant by the vent.

mach2

Original Poster:

226 posts

233 months

Friday 24th March 2017
quotequote all
ianwayne said:
Sounds like you may have a blockage in the fuel rail.

If you press the little schrader valve on the o/s of the fuel rail after initial ignition on, do you get a spurt of fuel out? If so, you have fuel pressure in the rail. Unless that is what you meant by the vent.
Yes, sorry, my description wasn't the best but there is no fuel coming out of the Schrader valve. Whilst I understand the thinking behind the fuel blockage I just can't see how it would have occurred? The fuel system hasn't been apart. I have had the plenum off but everything has been re-connected.

Sardonicus

18,928 posts

220 months

Friday 24th March 2017
quotequote all
How can you have fuel to the rail but none at the schrader valve that cannot be ? confused

mach2

Original Poster:

226 posts

233 months

Friday 24th March 2017
quotequote all
Sardonicus said:
How can you have fuel to the rail but none at the schrader valve that cannot be ? confused
My thoughts exactly but that's what I'm faced with. frown
When I disconnected the fuel feed at the rail and primed the pump the fuel was flying out so
to me the fuel is getting through. When I reconnected the pipe, primed the pump again and depressed the
Schrader valve nothing came out. Somewhat bemused by it.
My only thought could be that the regulator is somehow constantly open in overflow mode and is venting the fuel before it's getting to the injectors. Would that make sense?

phazed

21,844 posts

203 months

Friday 24th March 2017
quotequote all
The valve is probably fecked.

ClassicChimaera

12,424 posts

148 months

Friday 24th March 2017
quotequote all
He also has dry plugs?
Regulator?

ClassicChimaera

12,424 posts

148 months

Friday 24th March 2017
quotequote all
Question for the knowledgeable

If there's a question over signals from Ecu to injectors( for instance)
Can you by just cranking the engine over still feel the pulses by touching an injector to check. I've detected a failed injector wire by just feeling along each injector until I found the one that didn't pulse, but the engine was running on three (Mazda) so easy to feel the rapid clicks of the injectors opening and closing.
Can you still feel the pulses of the injectors with just cranking speed?

mark-tda4s

26 posts

95 months

Friday 24th March 2017
quotequote all
If youve had the plenum off, have you reconnected the vacuum pipe from the regulator valve to the plenum nipple under the stepper motor?

mach2

Original Poster:

226 posts

233 months

Friday 24th March 2017
quotequote all
mark-tda4s said:
If youve had the plenum off, have you reconnected the vacuum pipe from the regulator valve to the plenum nipple under the stepper motor?
Yes, it's re-connected. Would this make a difference if it wasn't connected? I assumed that pipe was effectively the overflow to vent excess pressure from the regulator?

mark-tda4s

26 posts

95 months

Friday 24th March 2017
quotequote all
As far as I know, its a vacuum pipe that pulls open a diaphragm in the regulator similar to the distributor advance, but I may be wrong!

Loubaruch

1,164 posts

197 months

Friday 24th March 2017
quotequote all
Assuming your fuel regulator is working OK.

You have priming so the fuel pump etc. is OK. But after priming when the engine is turning over feedback from the ignition circuit as I understand it causes the ECU to trigger fuel to be pumped continuously. I would as a first check change over the two relays in the passenger footwell. Or preferably put new ones in.

This may help:

http://www.bertram-hill.com/fuel-pump-schematic.ht...

Steve_D

13,737 posts

257 months

Saturday 25th March 2017
quotequote all
mark-tda4s said:
As far as I know, its a vacuum pipe that pulls open a diaphragm in the regulator similar to the distributor advance, but I may be wrong!
Correct. Varies the fuel pressure with engine load.

Steve

mach2

Original Poster:

226 posts

233 months

Saturday 25th March 2017
quotequote all
Thanks guys, I understand a bit more about the regulator now so will look at that in the first instance as it appears the fuel doesn't seem to be getting past this point. Pain in the arse though to change th thing.....

Steve_D

13,737 posts

257 months

Saturday 25th March 2017
quotequote all
You have already disconnected the fuel feed and proved there is fuel flow there but I don't believe you have proven that there is pressure.
Next disconnect the return pipe and see if you have flow there.

Steve

mach2

Original Poster:

226 posts

233 months

Saturday 25th March 2017
quotequote all
Steve_D said:
You have already disconnected the fuel feed and proved there is fuel flow there but I don't believe you have proven that there is pressure.
Next disconnect the return pipe and see if you have flow there.

Steve
Thanks Steve. I'm assuming if I have no flow at the return that the diaphragm isn't allowing the fuel to flow around the rail and its likely that the diaphragm is the culprit.

Sardonicus

18,928 posts

220 months

Wednesday 29th March 2017
quotequote all
mach2 said:
Steve_D said:
You have already disconnected the fuel feed and proved there is fuel flow there but I don't believe you have proven that there is pressure.
Next disconnect the return pipe and see if you have flow there.

Steve
Thanks Steve. I'm assuming if I have no flow at the return that the diaphragm isn't allowing the fuel to flow around the rail and its likely that the diaphragm is the culprit.
Its also a sure sign your fuel pump is knackered too, in these kinds of cases you always need to confirm fuel pressure is within spec

spitfire4v8

3,989 posts

180 months

Wednesday 29th March 2017
quotequote all
Sounds very much to me like youve put the pressure feed from the pump to the regulator, and the return line to the other connection on the fuel rail. IE you have your feed and return lines on the wrong way around.

mach2

Original Poster:

226 posts

233 months

Wednesday 29th March 2017
quotequote all
spitfire4v8 said:
Sounds very much to me like youve put the pressure feed from the pump to the regulator, and the return line to the other connection on the fuel rail. IE you have your feed and return lines on the wrong way around.
Thanks but that was one of the first things I checked. Luckily I have another
Chimaera close by that I could also check with.
I've also nabbed his fuel regulator and pump which I'm going to swop out in turn
tonight and see one or other or both cure the problem.

Steve_D

13,737 posts

257 months

Wednesday 29th March 2017
quotequote all
I would try testing the pressure first.
There is a valve on the fuel rail on which you can use a standard tyre pressure gauge. Just hold the gauge on and get someone to turn on and get the pump to prime. You are looking for around 38psi.
No point taking either yours or another car apart until you know the simple facts.

Steve