Cold start issue

[MassiveJim]

Shift it on and buy another car

Nah, I'm gonna keep it.
Don't know what this issue is but eventually I'm sure we'll resolve it.
I imagine 1 day it is going to fail to start completely, then we'll be able to find out whats wrong. :/

 

[MassiveJim]

fuel pressure gauge has now been connected to it.
its dropping fuel pressure pretty quickly. Its been sat outside for about an hour im gonna check it in a bit to see how much, but whilst talking to the mechanic for 10-15 minutes it dropped from 65 to 58ish.

connecting the gauge up dropped the pressure down to zero, turning on ignition brought that up to 40ish, then starting the car took it straight to 65

 

[MassiveJim]

so, left it standing for a couple of hours,
fuel pressure was at zero, turned the ignition on and it went up to 40, turned the ignition off and back on and it shot straight up to 65psi.

obviously something is allowing fuel to empty out and then air is getting in causing this cranking issue.

where would i find out if the ST220 has a fuel check valve and where it would be ?
if it doesn't then is it fuel pump ?

 

[Gaygle]

so, left it standing for a couple of hours,
fuel pressure was at zero, turned the ignition on and it went up to 40, turned the ignition off and back on and it shot straight up to 65psi.

obviously something is allowing fuel to empty out and then air is getting in causing this cranking issue.

where would i find out if the ST220 has a fuel check valve and where it would be ?
if it doesn't then is it fuel pump ?

I should think it'll be the seals in the pump which have failed.

I've just done some quick Googling and it appears as though error codes like "lean on bank 1 and 2" are very common when the pump fails as it just can't meet the demand of the engine. Rather annoyingly, on the Mondeo you need to drop the fuel tank to replace the fuel pump. It turns a nice quick hours job (if the FP is under the rear seat bench like in a lot of cars), into a 3 or 4 hour job!

 

[MassiveJim]

I should think it'll be the seals in the pump which have failed.

I've just done some quick Googling and it appears as though error codes like "lean on bank 1 and 2" are very common when the pump fails as it just can't meet the demand of the engine. Rather annoyingly, on the Mondeo you need to drop the fuel tank to replace the fuel pump. It turns a nice quick hours job (if the FP is under the rear seat bench like in a lot of cars), into a 3 or 4 hour job!

I haven't ruled the pump out as the cause of the starting issue, but i have kind of ruled it out for the lean running purely based on the fact that it runs lean on gas as well.
As for dropping the tank, I'm happy to cut a bigger hole in the floor under the bench, the car is 14 years old, other people have done it this way and reported that it makes it about a 30 - 60 miutes job

 

[MatteH Oxford]

Has anyone checked the fuel trim numbers? I reckon you've got a vacuum leak somewhere after the throttlebody if the car is running lean on both fuel + gas.

 

[MassiveJim]

Has anyone checked the fuel trim numbers? I reckon you've got a vacuum leak somewhere after the throttlebody if the car is running lean on both fuel + gas.

Smoke test was done and 1 pipe replaced.
Error code relating to the fuel purge valve came up so we replaced that and the code hasn't come back
since doing both of those the car has started to run noticeably better.

Fuel trims are slightly different on Gas and petrol (although that is to be expected really), they are always positive however, which ties in with it running lean (its trying to add more fuel to compensate)
I have also had a code come up that one of the O2 sensors was switching too slowly.

Next step is to replace both upstream O2 sensors (these are in my car waiting to be fitted), if this doesn't cure the lean running, I'll try changing the MAF.

And also I have just bought a 2nd hand pump off ebay, going to try that and see if it stops the fuel draining back.
I tried to find out if there was a non-return valve somewhere but I think if there is, then its all part of the fuel pump assembly/sender unit, ie not available seperately

 

[MatteH Oxford]

it will have a fuel pressure regulator that controls flow back to the tank, it'll be on the fuel rail. At idle (max vacuum) it's open to allow fuel to flow back to the tank because not much fuel is injected. As rpms rise and vacuum drops, it shuts to compensate for the potential drop in rail pressure due to the increased demand for fuel. A faulty one normally causes a lack of performance.

Have you checked the MAF to see if it's clean? if you have a scan tool watch for flow rate increase with the rpms (i.e. it should). If you drive and record the Fuel trim numbers, they will get worse with engine speed if it is dirty (as it will with a weak fuel pump or regulator). A vacuum leak will improve with RPM as vacuum drops the more the throttle is open, negating the effects of a vac leak.

************************************************

With regards to the O2 sensors, the ECU won't acknowledge any readings from them until the car goes into what is know as 'closed loop', this is when the engine is at a sufficient temperature for the readings from the sensors to be accurate. The ecu will use a set of parameters that vary according to input from a select few sensors during cold start and low temperature conditions.

AFAIK coolant temperature (possibly ambient air temp or intake temp), ignition timing and mass airflow are the usual inputs. Possibly a few more, it's been a while since i worked on cars full time!.

 

[MassiveJim]

Little update on this.
lean running engine appears to have been sorted now.
we replaced both O2 sensors and it was still happening.
so my local garage did his own smoke test and found a leak on the manifold just after the MAF housing, he has sorted this leak and the codes haven't come back.

The starting issue has resolved itself, however I know that it will come back eventually.
Garage tested the pressure overnight and it is now holding pressure, (it was dropping to zero when I had the starting issue)

So this sounds to me like a sticky valve or small crack in a pipe somewhere that is working loose sometimes maybe.

MatteH you mentioned the FPR, I am no expert so please correct me if I am wrong but I didn't think the FPR had anything to do with the back flow in to the fuel tank, I assume there would be a non-return valve somewhere, perhaps part of the fuel pump assembly ?

 

[MatteH Oxford]

On a typical petrol fuel injection system the FPR does control the flow back to the tank, when they fail the car performs poorly under acceleration as it will be starved of fuel (the fuel trim numbers will get worse during acceleration).

The other main alternative is a returnless system using a fuel pump that is voltage regulated. This system does not have a FPR (no need for one, just a pressure sensor to tell the ECU what voltage to supply the pump)


Glad to hear that things have improved, I had an inkling that you had a vacuum leak somewhere and it will most definitely impact on cold starts due to the too-lean mixture.

 

[MassiveJim]

On a typical petrol fuel injection system the FPR does control the flow back to the tank, when they fail the car performs poorly under acceleration as it will be starved of fuel (the fuel trim numbers will get worse during acceleration).

The other main alternative is a returnless system using a fuel pump that is voltage regulated. This system does not have a FPR (no need for one, just a pressure sensor to tell the ECU what voltage to supply the pump)


Glad to hear that things have improved, I had an inkling that you had a vacuum leak somewhere and it will most definitely impact on cold starts due to the too-lean mixture.

cold start issue didn't have anything to do with the air leak.
It is down to the fuel pressure dropping to zero over a period of a couple of hours, however this has stopped happening now, so looks like that is still intermittent. ill just have to wait till it comes back till i try and resolve that one.

 

[MatteH Oxford]

There is often a check valve located in the outlet of the fuel pump but it's mainly to ensure flow remains in the correct direction. The regulator shouldn't allow fuel through with the engine off, if it's removed then you shouldn't be able to blow through it (not easily anyway). If you can, it's faulty.

Besides this, flicking the key on/off a few times should prime the system enough to build up sufficient pressure to start the car without too much trouble(I'm sure you've tried this already?).

Still reckon the lean mixture was a significant contributor to the cold start issue.

 

[MassiveJim]

There is often a check valve located in the outlet of the fuel pump but it's mainly to ensure flow remains in the correct direction. The regulator shouldn't allow fuel through with the engine off, if it's removed then you shouldn't be able to blow through it (not easily anyway). If you can, it's faulty.

Besides this, flicking the key on/off a few times should prime the system enough to build up sufficient pressure to start the car without too much trouble(I'm sure you've tried this already?).

Still reckon the lean mixture was a significant contributor to the cold start issue.

fuel pressure was dropping off to zero, turning key twice primed it up to full pressure, and I had the starting issue, presumably because the fuel lines had been allowed to fill full of air once the fuel had completely emptied out.
Now it isn't dropping off and it starts ok.

interestingly its not idling as well on gas now (very easy to stall) presumably it needs the gas remapping now that airflow is being correctly monitored.
Its not terrible though, so ill live with it until I can be bother to find someone nearby to do it, or drive an hour out of my way to the place I went to before.

one thing I can say is it pulls like a train now that all the above work has been done, feels a lot better to drive now.

 

[MatteH Oxford]

The air will be purged during the time the fuel pump is priming. It doesn't matter if it's air or fuel in the system, once pressure gets to the regulated 4.5 bar then the FPR diaphragm opens and vents any air into the return line. A fuel line could be 99%+ full and yet show no pressure on a gauge, like if it is sat in a fuel can.

A healthy pump will supply fuel at a higher pressure than the FPR is set to, this means pressure is always potentially higher than required (as a fail-safe) and a continual flow of unused fuel will be returned to the tank.

They may be a small amount of residual air between the rail and injectors but not 20-30 seconds of cranking worth. The poor starting would have been down to the vacuum leak, just like trying to start a vehicle with a carburettor and no choke on a cold day.