Hi Guys,

As the title says, I've just had the engine replaced in my Verada.

With the old engine, I had a surging problem when running on petrol but not LPG. The car would surge when it hit around 3500 RPM and would completely lose power. Even when gradually building up to 3500 RPM it still surges. Not speed related, because I can cruise on the freeway at 110 km/h as long as I keep the revs low. Car revs normally while in neutral.

Now with the new engine, the problem is still there. Feels like it has gotten slightly worse over time. I've had the spark plugs/leads replaced. Because the problem is only with petrol and not LPG, I have a feeling it could be the fuel pump.

Does anyone know what this could be?

I'd be thinking fuel pump or filter, can't think what else it could be if you've swapped the motor. I vaguely recollect reading that the filter element can break down under high demand, blocking fuel flow.

Hmm... would that cause surging 100% of the time though? The problem doesn't seem to come and go, it's always been there.

I don't know, to be honest. I'd say one or the other is probably the best bet, depending on what was swapped out along with the motor. Obviously you're looking for something that wasn't swapped, possibly the ECU but from the way you describe the problem it sounds more like a fuel thing. Does the surging happen bringing it up to 3500 in neutral, ie. in the garage, or only under load?

It doesn't surge at all when brought up to 3500 in neutral, and revs freely. Seems to be only under load, but it still happens when on the highway and gradually bringing it up to 3500.

how is it under wide open throttle? better? worse?
What about at high rpm, lock it in first and take it up to 60kph and hold it. Should be doing somewhere around 6000rpm, surging? no surging? drop down to 50kph, sit there for a bit, then floor it to 70/75kph and observe

If it's smooth at high rpm it's more likely to be electrical, if it's significantly worse it's likely to be fuel. If there's no real correlation it could be anything

I'd be tempted to find your friends really really long private driveway or race track, lock it in 2nd and hold it flat to at least 150kph. If it's fuel related - or at least lack of fuel - it'll perform like utter crap trying to get there. It would give you a few seconds of consistent wide open throttle to evaluate better. If it's just 'spotty' and not really different to pootling around town. Then i'd say it would be safe enough to say that fuel is ok, or at least know its not the only problem

It's worse under wide open throttle, though it still only starts around 3500 revs. I don't think the car can make it to 6000 RPM under load, because as soon as it hits 3500 there's a total loss of power. I think it's likely to be fuel related. I don't think I've been running the car on petrol as much as I should have. The injectors were cleaned when the new engine was put in, so it isn't those. Could it be a bad fuel pump?

Sounds like fuel pump to me.

The reason it revs freely in neutral past 3500rpm is because that needs a lot less fuel.

With the car in gear and a load on the engine, exceeding 3500rpm is requiring more fuel flow than the pump/blocked filter can provide.

That's my best guess.

Is also worth checking the fuel tank to see if any rubbish has collected around the fuel pump pick up pipe/strainer.

How old is the fuel in the tank, things like filter being blocked as well as pump can do this as the engine will starve for fuel under load, avoid driving like this until you get sorted however as this can do a lot of engine damage

The fuel that's in it now is only a few days old. I filled it with 98 octane today and added some total fuel system cleaner, but so far the problem is still there. Would a faulty fuel pump carry on for a few months of driving though? I thought it would have died by now. The fuel filter was replaced 10,000km ago.

Your first comment that it was fine on LPG but not on petrol would eliminate most electric problems like spark etc so I agree with other posters that it looks a bit like fuel pressure.

A) Fuel Pump, b) The fuel pressure regulator might be tripping out too soon.

P.S. My old TH Wagon had an 'Unofficial' recall on fuel pump (I had problems with the trip computer going to --- for range all the time) apparently there were some pumps not up to spec.

Problem has been solved by Brendan and Mal at Mits-Fix. Turned out to be a bad MAF sensor!

Thanks for posting the fix - it helps a lot of forum searchers - and ++ Mits-Fix nice job.

Thanks for posting the fix - it helps a lot of forum searchers - and ++ Mits-Fix nice job.

Actually, it seems like I spoke too soon... The MAF sensor definitely improved my acceleration, but the surging problem is still there. Thinking of replacing the fuel pump next, but I'm not sure.

I had this happen to my old XI, it would struggle and have no power and giant flat spots then take off!

I changed the engine and gearbox to a 3.8 and 5 speed auto and it just got worse and worse over time.

Try unplugging the O2 sensor on the passenger side near the ECU. It worked for me.

Basically, when these sensors die, they stop sending a signal. The ECU goes to a default fuel map and then just uses more fuel all of the time.

With mine, it was sending corrupt signals so the ECU would cut off the fuel or add it or whatever. So unplugging it tested the theory and it worked.

Mike

Update: It seems like the problem is only happening when the engine warms up. I took it out this morning and while the engine was still cold I opened the throttle completely a few times and it ran perfectly! Then once the temperature gauge reached the middle the problem started again.

Try unplugging the O2 sensor on the passenger side near the ECU. It worked for me.

Basically, when these sensors die, they stop sending a signal. The ECU goes to a default fuel map and then just uses more fuel all of the time.



Sorry, I forgot to mention that I also had the O2 sensor replaced yesterday at Mits-Fix and no luck. It certainly improved performance, but the problem is still there.