View Full Version : Flat spot - ND boost upgrade
Just had a new turbo fitted and at the same time fitted the ND boost upgrade, boosting about 14psi. Also got a Mongoose stainless system. Now, with the extra boost I have a flat spot (more than a spot really) at about 4000-6000rpm. Just as the turbo gets up to full whack there's a loss in power, at the same time the induction noice changes from a nice hiss to a whistle.
It's also more pronounced with the throttle open fully ie booting it. If I gradually increase throttle it'll get through the flat range without too much trouble but that's a bit useless.
It sounds like the turbo just can't suck enough air in, could this be the problem?
I've yet to fit my K&N. My mate is also having EXACTLY the same problem with his ND boost upgrade, but he has a K&N and std exhaust rather than std filter and Mongoose.
Thought it might be a breathing thing.. any help appreciated, thanks
Carl
Is it doing it only when the revs are high OR if you plant your foot down in 5th and let it boost up while keeping the revs low? It sounds like a leaky boost pipe somewhere, especially with a hiss. The K&N will hiss but you aint put it on yet so it kinda rules that out. Def sounds like a boost leak though. Id run around and check all the clips before worrying too much.
SteveSadler
31-05-2001, 13:20
Carl,
seems as though your engine is making good power.
Time for an uprated fuel pump mate.
Thats what u need.
Standard S13 pump is crap. only good for 230/240hp.
Once thats in , you'll be fine.
whats happening is the engine is leaning out and the ECu is trying to knock back the timing to compensate.
Minor problem, but avoid flooring it.
I had the same problem on mine. If you reset the boost to 9/10psi you'll find the car will be ok.
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Bayside Blue S13
Mild Mods
I reckon about 230hp/210Ib
I believe matt_j posted a comment on the board somewhere which related to this slightly.
He had a T28 and Boost upgrade performed a week or two ago from Norris, and was having a kind-of flat spot problem. I think it might be his chip activating the fuel cut on overboost detection as he hasn't yet chipped it and it gives that impression. Not to be confused with what I thought was overboost, which was in fact massive underfuelling causing my car to jerk around under acceleration (£30 fix ... mutter).
I'm going for a boost upgrade very soon now also, but with an intercooler, which quite possibly would stop any flat spotting that seems to be associated with the boost upgrade. Also I'll be getting a chip so there won't be any fuel-cut issues hopefully.
Yet I'm not that optimistic as the car produces so many random noises, Simon will probably take one look at it and cry.
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Graphite Grey S13
HKS Hiper Muffler
Suspect suspension
Chimp, Only does it between 4000-6000 and only when accelerating hard. if i accelerate gradually it's nowhere near as pronounced and it will rev up to 6000 no probs. Shouldn't be any boost leaks, measured consistent at 14psi.
Steve, The only mod i've got is the mongoose and the actuator which is turned up to 14psi, if i turn it back down to 10 i might as well have a standard. at 14-15psi with a k&n and mongoose it should only be up to around 200bhp so the fuel pump shouldn't really be an issue should it?
How much am I looking at for a fuel pump btw?
Ta
Could just be a case of the boost dropping off with the higher revs. When I had my T25 and std intercooler, it would boost up to 15 psi at about 4000, but as it got up to 5,6, and 7000rpm the boost dropped of to a measly 8psi. http://300zx.co.uk/200sx/ubb/confused.gif
Theres a hooj thread about fuel pumps, costs vary from tiddly to as expensive as you dare. It may be underfuelling, but Id also try the K&N, the turbo might be trying to suck your standard airbox thought the intake pipe. http://300zx.co.uk/200sx/ubb/wink.gif. The airbox is every bit as shoddy as the standard intercooler, I would have thought 14psi wouldnt cause much of an underfuelling problem unless the pump is totally knackerd. The standard chip can run up to 16psi without boost cut or fueeling problems.
OK, thanks all. Think i'll bung me K&N on tonight and see what happens.
Cya
olly200sx
31-05-2001, 14:57
I had exactly the same problem for ages and found it to be one of three things , 1. fuel cut coming in, but you would definately know it as it cuts out completely momentarily and then rockets off down the road. 2. the spark plugs weren't at their best and replacing them made a vast improvement as the old ones were all covered in carbon through overfuelling, which brings to my that was. 3. I changed the engine temperature sensor for £21 and this corrected the overfuelling which you could be experiencing, this leads to caking the spark plugs in carbon and making it very hard for them to spark. Just some suggestions, change the plugs or at least look at them, check the temperature sensor.
Hope this helps.
olly200sx
31-05-2001, 14:57
I had exactly the same problem for ages and found it to be one of three things , 1. fuel cut coming in, but you would definately know it as it cuts out completely momentarily and then rockets off down the road. 2. the spark plugs weren't at their best and replacing them made a vast improvement as the old ones were all covered in carbon through overfuelling, which brings to my that was. 3. I changed the engine temperature sensor for £21 and this corrected the overfuelling which you could be experiencing, this leads to caking the spark plugs in carbon and making it very hard for them to spark. Just some suggestions, change the plugs or at least look at them, check the temperature sensor.
Hope this helps.
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S13 - Lots of Mods
olly200sx
31-05-2001, 15:33
One more thing to check would be the exhaust mounting nuts from the turbo to downpipe, when I checked them even though you couldn't really hear it they were all lose and when tightened it made the world of difference, that could also be why your hearing the hissing noise....
My extra 2 cents worth
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S13 - Lots of Mods
AHAAAAAAAA!!!!! I think that'll be it ^^^^
Caution tightening them though *ping*!! I snapped 1 then 3 more trying to get it back off to have the first one drilled out. Just dont swing off em like a ermmm Monkey..
Well, the K&N's on now and it sounds great with the induction roar, wastegate chatter, growling from the mongoose and pop's at gearchange :-) however it didn't sort the loss of power :-(
Sure it's not the fuel cut off, it doesn't die, it just doesn't accelerate properly between 4-6k
The turbo was fitted by a garage 3 days ago so i'm pretty sure all the manifold gaskets are tight + can't hear any blowing from under the bonnet.
spark plugs are brand new. they're the cold plugs that come with the boost upgrade
where's this temp sensor located?
reckon it'd be worthwhile cleaning up the airflow meter?
thanks all
carl
SteveSadler
01-06-2001, 14:29
seriously consider your pump. It could be that its just weak. If not. Do the cheap thing first and change your fuel filter (located to the left of the inlet chamber)
£5 from Halford.
This can clogup and cause restriction. But from what you've described (gradual throttle ok and heavy throttle lack of power) this sounds like the Fuel Pump.
S13 pumps are weak and most tested only produce around 230hp
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Bayside Blue S13
Mild Mods
I reckon around about 240BHP.
Found the problem - timing.
Timing was set by the garage who fitted the turbo with the throttle sensor still attached. As soon as you adjust the timing, the ECU compensates and cancels it out. Eventually you adjust so much that the ECU can't compensate anymore and that was causing problems at 4-6k rpm.
Solution - disconnect the throttle sensor, adjust the timing (and slow idle bolt if it needs it) and voila! sorted. When you reconnect the sensor, the ECU seems to reset itself and can adjust properly at the higher revs.
My mate had the same symptoms after a ND boost upgrade and this solved his problem too.
Thanks for all the suggestions though.
Carl
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