M20B29 hesitation at WOT above 5k

[digger]

Sounds like you have fuel pressure issues those wot numbers are way off what they should be

[sert57]

Yeah before putting in the 2.9 I had a stock b25 that ran well with the same ignition coil, AFM, ICV, CPS, and ECU.
Just finish building the newer motor and have been shaking it down and breaking it in. New Bremi Caps/Rotor/plug wires and bosch plugs. different TPS that seems to work fine. Other than the described issue she runs very well.

Haven't picked up a wideband yet, but if i keep having issues I will.

Checked plug gap, it was all just a hair above spec so I bent them in spec. didnt fix it. Spark plugs look like its running a little lean but not too bad.

Changed out for the oem chip, didnt fix it, put the custom chip back in.

measured ignition coil resistance to be .6/6300 which isn't too far out of spec ( considering what others have gotten), but potentially worth looking at.

I recall when i changed the fuel filter out the original was backwards, so i double checked the orientation of mine and it was fine.

I T'd in a fuel pressure gauge and went for a spin, at idle I was getting around 37 psi and at WOT the gauge went a little hectic but seemed to stay above 25-30 psi for the most part.

I'm thinking ignition coil is the next shot

[digger]

yeah, its easy to plug in a stock chip for a sanity check.

presumably the engine ran great before any of this? if so you are probably taxing the system too much so its either a mapping thing, fuel delivery issue or spark delivery issue which probably somewhat helps rule out AFM, FPR assuming those are carried over. i wouldnt rule out the coil. i wouldnt be looking at the ICV, CPS or vaccum leak. the TPS requires continuity checks. issues ive had with plug wires provided random missfires rather than this kind of issue.

had the exact same symptoms on a s50b32 just the plug gap being about 2mm, increasing rpm and cylinder pressure (load) taxes the ignition system more.

you will probably want to invest in an WB O2 sensor, as somewhere down the line you are going to need it anyway if you start upgrading stuff further (like the ECU to MS) and it will straight away tell you if its fuel or ignition with this issue otherwise a shop with a portable O2 setup will be able to help

[e30davie]

What guarantee is there that the sssquid tune is actually tuned for your engine? I mean i know the sssquid has a good name and all, but to me its the black box of unknown in the equation. Do you have a wideband o2 on the exhaust to see if its leaning out?

The WOT swtich is a good suggestion, but im not exactly sure how the motronic works, i would have thought that the AFM would still measure the air coming in and giving enough fuel regardless of the WOT switch.

Spark break down is the other option, have you gapped the plugs? what color do the plugs look like? do they look like the engine is lean or do they look black like the spark is breaking down and not burning the fuel?

[digger]

My gut tells me either an ignition issue (spark breakdown) or its way too lean e.g the wot switch Isn't being activated or fuel volume delivery issue . I don't play around with motronic anymore though.

[sert57]

I've been sorting out all the kinks on my 2.9L build and am getting confused with the last little issue.

Issue:
The engine falls on its face at WOT above 5k rpm. It will continue to pull to redline but it is choppy and not nearly as powerful as 3/4 throttle. It is fine at 3/4 throttle going all the way to redline, and fine at WOT up to 5k. It almost seems like a fuel starvation issue but I cant identify a culprit that would do it ( see below)

Specs:
M20 2.85L ( S50US crank, eta rods, B25 pistons)
Bimmerheads 272 w/ nuk cam gear
IE HD Rockers
IE headers to custom midsection w/ O2 sensor bung
M52 pink top injectors
SSSquid custom chip to above mentioned specs

Potential culprits:

AFM: Potentially? It worked fine on my car before the build, but it has never seen the higher volume of air before that WOT would give. I could certainly see where there is a dead spot because it is not worn in on the higher airflow.
TPS: I tested the resistance and it works fine at idle and WOT
CPS: doesnt make sense with the issue only at WOT
ICV: doubftful because not idle
Vacuum leak: once again, doesnt make sense to me since it works fine at WOT from 4-5k
Chip: Initial instinct, but i had it reflashed for a few small adjustments i wanted to make ( redline and octane) and it still does it. i am doubtful
injectors: it has done the issue with the M52 pink tops, ford injectors, and known good oe b25 injectors, so i am doubtful
Fuel Pump: I installed a new meyle unit very recently, so I'm doubtful. I can T in a fuel pressure gauge and do a pull, but it gave ample psi at idle. Before the new fuel pump the old one would do the same issue
FPR: maybe? mine appears to work fine at all other situations though.
Spark Plugs: New Bosch units, i used the same type on my old b25 and they worked well, and I'm unsure how the WOT would affect this.
Ignition coil: potentially? I believe its still the original one, but it works fine at 3/4 throttle so I'm doubtful.

Does anyone have any ideas?

Thanks!
-Ken