Power Flat Spot

[sean_co]

Good evening all,

hopefully someone here will be able to assist me in tracking down an issue. this recently started and is not 100% constant. under WOT through the gears there is a flat spot in power deliver from about 4600 rpm to about 4800 rpm, this becomes more noticeable in the higher gears but always between that rpm range. up to that rpm it pulls strong and the same beyond that rpm

i have taken the car to Lexus to have it checked they told me they had it on the scanner on a test run and found all o2 readings were showing lean during that rpm range. they then tell me they can not trouble shoot further because of my decat and PPE engineering device. i dont agree with them that those are causing the lean condition since it only recently started doing this. unfortunately our dealerships here love to blame the decat for anything they cant find. i replaced the MAF and it feels better, not always holding back the power now but it does seem to happen after driving for some time. the one day this happened i also noticed a slightly longer than normal crank to start time, by longer im talking a sec or two more, nothing major but not usual.

there are also no error codes as per Lexus and also no CEL. no cylinder miss fires in live or history.

could this be a sign of a fuel tank pump going bad?

the vehicle has the below changes

1) primary cats hallowed out (previous owner)

2) removed secondary cats (previous owner)

3) ppe sim (installed myself to fix the CEL from above 2 mods)

4) airfilter (installed because the garage said it was not done in the Lexus 90k service) - recently checked it and it is unfortunately aftermarket filter

regards,

[Stuno1]

Hmmm. That's very specific. I'd take it to a rolling road to have the car run and look at the power curve. I can't imagine gutting cats is any good as it would almost certainly change the bore of the exhaust system at that point which may do some odd things and invariably reduces back pressure.

[sean_co]

Hmmm. That's very specific. I'd take it to a rolling road to have the car run and look at the power curve. I can't imagine gutting cats is any good as it would almost certainly change the bore of the exhaust system at that point which may do some odd things and invariably reduces back pressure.

Thanks Stuno1 for the quick reply.

i do agree that running standard headers with gutted primaries is not optimal by any means although its been running fine up till a month or two ago. i can't really put my finger on the beginning of this issue since i usually just cruise around.

i will defiantly take up your suggestion and put it on the dyno to check that curve out. luckily I'm on leave today and there is one down the road from where i stay

[Stuno1]

Hmmm. That's very specific. I'd take it to a rolling road to have the car run and look at the power curve. I can't imagine gutting cats is any good as it would almost certainly change the bore of the exhaust system at that point which may do some odd things and invariably reduces back pressure.

Thanks Stuno1 for the quick reply.

i do agree that running standard headers with gutted primaries is not optimal by any means although its been running fine up till a month or two ago. i can't really put my finger on the beginning of this issue since i usually just cruise around.

i will defiantly take up your suggestion and put it on the dyno to check that curve out. luckily I'm on leave today and there is one down the road from where i stay

Be interesting to see the read out chap.

[Peter P18]

Not sure how I missed this?! :(

Any news? Hopefully you've got to the bottom of it, or at least had it on a dyno?

Sounds odd that it was running fine for a while before you started having the issues?!

Hopefully it can be remedied relatively easily.

Cheers.

Pete

[sean_co]

Unfortunately i have not yet had it on the dyno, the one close to me is booked up to early Jan and want to charge a silly amount for a run. I went down to the coast for a funeral last weekend and down there it performed 100%. We live 1700M above sea level, strange that it ran 100% down there though. we are going down again in the next week so ill have to test some more :)

while we wait for the dyno early jan i will check the fuel filter (in tank i believe), air filter and perhaps clean the MAF (which is new)

[Womble72]

This may well be a silly question or statement, have u used any supermarket fuel?......I always run mine on BP ultimate, will NEVER put supermarket fuel in it, my M3 would have flat spots in acceleration if I used anything other than high octane fuels, I've not run my F on anything other than high octane. And I've been told of additives supermarkets add to maximise profit, thus, cheaper prices

[sean_co]

This may well be a silly question or statement, have u used any supermarket fuel?......I always run mine on BP ultimate, will NEVER put supermarket fuel in it, my M3 would have flat spots in acceleration if I used anything other than high octane fuels, I've not run my F on anything other than high octane. And I've been told of additives supermarkets add to maximise profit, thus, cheaper prices

Hi Womble72

In the time I have had the F I have only used petrol from stations like BP/Caltex/Shell. Those are really the only places we can get petrol where I live. I only fill up with 95 octane, we have 2 options that's 93 and 95 even at the cost. I usually only fill up at one station I'll try a different brand but same octane, perhaps the brand made a change to their fuel.

When your m3 had these flat spots were they always at the same rpm?

Just to follow up on my previous post. I have cleaned the Maf and changed the air filter (now oem filter), it was dirty. Still have the flat spot at altitude but again I am visiting family at the cost and there is no flat spot down here. This is with the same fuel I filled up with at altitude. Will test again in a few days to be sure.

Do these cars also have a map sensor?

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[Womble72]

From memory I'd say yes, only way I can describe it is, felt like it was farting under load/acceleration, the fuel I use has an octane level of 97-99 depending where I fill up, BP ultimate or shell V power nitro, did a 700 mile round trip into n through the Lake District with no issues, u maybe able to buy an additive to put in the tank, might be worth looking into

[sean_co]

From memory I'd say yes, only way I can describe it is, felt like it was farting under load/acceleration, the fuel I use has an octane level of 97-99 depending where I fill up, BP ultimate or shell V power nitro, did a 700 mile round trip into n through the Lake District with no issues, u maybe able to buy an additive to put in the tank, might be worth looking into

Are you talking about an additive to increase the octane a bit?

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[Womble72]

Yes, not sure if there is such a product, but 95 is quite low, I know the car will run on it, but if u can increase it it may eliminate the issue, u may well find that the advise would be to add every 4 or 6 full up, IF there is a product, it will definitely be the cheapest place to start

Paul

[stevet]

I always used Morrisons 95 standard in mine and never had any issues.