Loss of power?!

[wongger]

I have an rb20 in my 240. One problem that has been bothering me for awhile. Sometime when I hit boost (sometimes even before) the car will just lose all power. I could floor the car and it wouldnt move one bit. It usually continues to stay like this until I switch gears (sometimes will continue) or let off the gas and wait 2-10 seconds.

Been told that this is a vacuum leak. Wondering if it could be anything else before I start changing all my hoses lol.

Also been told it could be a faulty FPR? not really sure though

Thanks in advance!!

[wongger]

Also, it sometimes has a bouncing idle (continually revs from 1k to 2.5k) until I turn it off and wait a little while.

[nelsonmxmarc]

How healthy is your fuel pump?

I'd swap your fuel filter as well, could be buggered..
But seeing as you did a swap, i'm sure you've changed this already?

Bouncing idle is not normally vacuum related. 1. boost leak won't cause idle to fluctuate since you're operating in vac. 2. A vac leak will likely cause a LEAN condition, say, somewhere in the 17 afr range. If you've got an AFR gauge handy, i'd keep an eye on it, you'll know off the bat what's going on.

I had a serious air leak on my motor when one of the injector grommets on the block fell inside. Ran a steady 17 afr at idle @ 1700 rpm. Under boost however, the car operated normally as the vac leak made absolutely no difference.

I'd check your MAF. Maf issues are characteristic of sporadic power loss when they're on the fritz. It's possible a few connections inside have come loose and need to be re-soldered. Check the How-to on that in the DIY section.

As for your weird idle, could be your AACV solenoid is buggered, TPS is on the way out or improperly adjusted causing discrepancy between the ECU monitored idle values of the AACV, and the TPS voltage.


Anyways i digress; check your fuel pressure. If you've got a good pump in there, check for kinks in the lines, know the integrity of your fuel filter, and then swap out the FPR to see if it makes any difference.

The more i read this, it does seem fuel related..

[wongger]

Yah I dont believe it is fuel related either. I was using the stock ka24de fuel pump earlier and it was still doing it. So I upgraded to the walbro (still runs the same). I changed the fuel filter last year to a 300zx one. Worked fine on the ka. Been underneath the car a fair bit, haven't seen any kinks or anything.

I dont have a afr, will pick one up this week hopefully.

I cleaned out the AACV before I installed the motor. Any chance that it is gummed up again? It ran great for a weeks after we got it all running. Its been doing this on and off for about 2 months now though.

I was thinking it was maybe the maf. Ill have to go through all the connections later on

Thanks for the help! Really helped me out!

[Skym]

Check o2 sensor, as when stuffed, ECU can make engine fluctuate from lean (revs rise) to rich (revs drop). Unplugging o2 sensor should tell you straight away if it's the cause (ECU goes into open loop, ignores o2 sensor, which ECU normally does at WOT or initially while warming engine up from cold).

Also check AACV to ECU idle calibration if above doesn't work, as set incorrectly, ECU idle rpm can bounce between what's set on ECU and what AACV screw is set at.

From what I can remember of how to adjust AACV to ECU calibration -

Note position of screw / diagnostic pot compared to lines on sticker surrounding hole on side of ECU and note how many turns when turning screw. Then turn screw on side of ECU all the way to left and disconnect AACV plug (stops ECU playing with idle rpm) and adjust idle rpm to 650rpm (what it's set at on ECU for RB20DET) via AACV screw. Plug AACV plug back in to see if idle rpm remains the same (650rpm). If it does remain at 650rpm, return screw on side of ECU to where it was (run mode) and your done. If not, unplug AACV plug and adjust idle rpm again.

Airleaks can make idle fluctuate a little bit, but not make idle bounce that much. Airleak behind MAF via loose intake hose clamp or crack in rubber intakepiping can make engine stutter, especially after exiting motorway / highway.

When MAF is not detected / unplugged, ECU can limit rpm (limp home mode) to 2000rpm or 3000rpm, can't remember which (I'm tired), as sometimes one of those rpm limits mentioned can be misinterpreted as ECU going into limp mode when ECU is faulty and engine runs excessively rich. Engine can start without MAF, learnt this when I accidently forgot to plug MAF in. Aftermarket ECU's can't do this, so is a unique to stock ECU feature.

[wongger]

So im not exactly sure what you wanted me to do with the o2 sensor, but I unplugged it and it ran the exact same lol. My idle only fluctuates when the car is losing power while drive (when I put it into neutral - it either stalls out, or idle surges) and it doesn't even do this very often.

My concern is just the constant loss of power. Some days it works great. On the way back from cscs yesterday it wouldn't rev over 3-4k, but even in the lower rpm it would still loss power than kick in again.

By losing power I mean the car acts as if its turned off as im driving (wont idle, wont rev)

I have been told it could be a faulty knock sensor?

Thanks again!

[wongger]

Also how many wires are running to the TPS? I have the top 2 in the plug, but the bottom one is either missing, or became disconnect?

[wongger]

Alright, So I thought I fixed it but the other day it started really acting up. I got a wideband, when it starts to happen the car leans out like crazy (16.9).

I had a feeling it was the maf, so as the car was on I ran my fingers along the wiring. Sure enough the car would stall out at certain parts of the wiring. So I fixed it, but now its happening again. Should I just replace the maf? or could it be the wiring again? or is it something else.

Need help please!!

[Skym]

From memory, faulty knock sensor = ECU won't let engine rev over 5000rpm.

Unplugging o2 sensor removes it as a cause of the problem. It seems problem might be TPS or MAF related. Wires falling out of MAF plug is common (someone pulled on wires when removing plug) or on ECU side. Or bad solders on opposite side of plug, inside square part of MAF can cause problems. You'll need high temp black silicon sealent to reseal square lid (protects from water, dust, etc), if you remove square lid on MAF to resolder. HICAS ECU, MAF, engine ECU, dash, etc suffer from bad solder problems.

If missing wire on TPS (auto to manual conversion???), it could mean engine is running suddenly lean. TPS is like an accelerator pump on carb engine that provides extra fuel to engine to stop engine running suddenly lean when throttle plate inside throttlebody suddenly opens.

[wongger]

I think im going to pick up a new maf if the price is right, and get new wires and plug. See if that works.

I dont think it is my knock sensors anymore, because the car revs over 5k, it seems to have the most problems during highway driving (constant mid-high rpm).

I rechecked my TPS and all the wires are there, I was looking at the wrong plug lol. I still think it could possibly be the problem though. Ill try the new maf and wires, cant hurt.

Thanks again