Thread: '98 P38 Overfuelling

Just found the vacuum hose for the fuel pressure regulator. It is in pretty bad shape. Has a crack in it. No signs of major fuel leaks, but I'll be replacing that asap. Could that be the cause of over fuelling?

Originally Posted by RangerFelix

Just found the vacuum hose for the fuel pressure regulator. It is in pretty bad shape. Has a crack in it. No signs of major fuel leaks, but I'll be replacing that asap. Could that be the cause of over fuelling?

Absolutely. a leaking vac hose at the reg means higher fuel pressure at light load which means extra rich as the fuel map can't cope. I see this all the time.

Okay. I've replaced the hose. Had a little drive. No noticeable improvement. The old one seems to still be able to hold a vacuum. Still taking too much petrol. (18l/100km empty & nothing on the roof rack on a country road at 50-60 - according to trip computer)



Just checked the fuel pressure at the rail again. 29psi while idling and 20psi with the engine off and ignition on. I checked it with a tyre air pressure gauge. That's too low right?

Also just cleaned the oil separator. That was a bit messy. Likely the engine had a hard time breathing through that. Will see how that affects the engine running tomorrow.

Originally Posted by RangerFelix

Okay. I've replaced the hose. Had a little drive. No noticeable improvement. The old one seems to still be able to hold a vacuum. Still taking too much petrol. (18l/100km empty & nothing on the roof rack on a country road at 50-60 - according to trip computer)



Just checked the fuel pressure at the rail again. 29psi while idling and 20psi with the engine off and ignition on. I checked it with a tyre air pressure gauge. That's too low right?

The pump pressure should climb by about 10psi when it is at full load as the injector pressure is supposed to be held at a constant level above manifold vacuum. You can mimic full load by temporarily undoing the vacuum hose. Unfortunately it sounds like your system is working normally and your problem is elsewhere.

BTW I wouldn't trust a dash readout of l/100km all that much. You should calibrate your settings by driving fill-to-fill and checking the odo against a GPS or road markers on a highway. You could easily be 20% out overall.

Out of curiosity RangerFelix, what size are your tyres?

Originally Posted by Keithy P38

Out of curiosity RangerFelix, what size are your tyres?

265/70 R16 BFGoodrich All-Terrain T/A



Running them at 34psi all round.



They are Muddies that the previous owner put on there. Really annoying, because they are too big so when the EAS is in access mode the tyres hit the wheel arch when turning.



These no doubt contribute to the bad fuel economy. I will change them, but only after this trip, so in about 3 months.

Originally Posted by RangerFelix

Okay. I've replaced the hose. Had a little drive. No noticeable improvement. The old one seems to still be able to hold a vacuum. Still taking too much petrol. (18l/100km empty & nothing on the roof rack on a country road at 50-60 - according to trip computer)

Hi

I would not place a lot of credence on the trip computer consumption figures, it is an average based on how much fuel the injectors are getting so it may take a while to see nay change there.

Much better to fill the tank and do it the old fashioned way

Steve

I'm not placing much trust into the trip computer figures. The figures from the initial post are calculated from the tank fill and km. I was just looking for some ballpark figures. The last couple of fills were very accurate on the trip computer for me.

Will be doing a bigger trip today, so I'll know of there's any change. Likely I'll still fit a new MAF and o2 sensors.



A blockage in the crankshaft breather (oil separator) wouldn't cause excessive fuel consumption, right?