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Discussion Starter #1
Hi,

My 93 VR4 was running amazingly until this week. All of a sudden, the car won’t boost past 6psi, even at 6psi it runs leaner than normal (12.5 vs 11.2), the fuel trims all went maxed adding fuel, and I’ve had to adjust the entire air map on my Apexi NEO to get it to run right. I’ve been running this tune for a while so something just went bad. Here is a relevant mod list:
  • 13Ts
  • K&N FIPK
  • GFB blow-off valve
  • Full exhaust with gutted precats
  • 550cc Delphi injectors
  • Supra pump, 3SX fuel system with billet filter, aftermarket regulator, RDR wiring upgrade, braided lines
  • NGK Iridium BKR7 plugs, new wires, new coils, new condenser
  • Apexi NEO
  • AEM Truboost
  • AEM wideband
  • Replaced caps in ECU
  • Deleted ECS computer (coilovers)
  • .....there’s a ton more but this is a decent summary
Recently and BEFORE the issue I have I did the following:
  • Installed the turbos
  • Installed the 550cc injectors
  • Installed the NEO and tuned using HHH datalogger and wideband
  • CHANGED UPPER AND LOWER INTAKE MANIFOLD GASKETS
  • Replaced the O2s with new NTK sensors
This issue just started happening but for weeks since the last round of work the car has been running amazingly. So far I’ve checked:
  • Intercoolers hoses, Y-pipe, etc for leaks
  • Pulled plugs and they look good although some look a little leaner than others
  • Pulled upper intake manifold and retorqued
  • Checked fuel pressure stationary (reads 40psi under vacuum and 50psi under load as set)
  • Swapped NEO for a new one, problem still exists
  • Removed GFB blow-off valve, disassembled and cleaned (thought it was sticking)
  • Checked for stuck open wastegates
  • Replaced MAF
  • Checked injector resistor box
  • Datalogged and everything looks good - at WOT both O2s read 0.93-0.95 and track together, 3-5 counts of knock occasionally at tip-in
I’m thinking these are the leading candidates (low boost and LEAN condition)
  1. There is an intake tract leak somewhere (lower intake manifold to heads maybe) - this would make it run lean and would leak boost
  2. The ECU is faulty
  3. New injectors are either clogged or faulty - wouldn’t explain low boost
  4. The fuel pump or fuel pump resistor/relay circuit is hosed - same
  5. Fuel filter is clogged - same
I’m currently stumped and am about to rip the top end off again to check the injectors and intake manifold. Any thoughts on what I may be missing?

Thanks,

MJ
 

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As easy as it is to do (relatively) I would pull the ECU and give it a good looking over.
Do you know if the capacitors have been changed? If not, there is a VERY good chance that one of more of them have failed.
Signs of failure are BULGING, LEAKING A VERY ACIDIC FLUID, and possibly compromised traces on the circuit board from the previously mentioned fluid.

I think you've ticked all the boxes from what I'm reading, but I would wonder why you feel there is a lower intake leak, since you just replaced the upper and lower gaskets.
Any chance the gaskets got compromised somehow during install. Proper torque on all bolts?

I will try to keep an eye on this thread as I am very interested to see the outcome...

Good Luck,

Bob.
 

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Discussion Starter #3
As easy as it is to do (relatively) I would pull the ECU and give it a good looking over.
Do you know if the capacitors have been changed? If not, there is a VERY good chance that one of more of them have failed.
Signs of failure are BULGING, LEAKING A VERY ACIDIC FLUID, and possibly compromised traces on the circuit board from the previously mentioned fluid.

I think you've ticked all the boxes from what I'm reading, but I would wonder why you feel there is a lower intake leak, since you just replaced the upper and lower gaskets.
Any chance the gaskets got compromised somehow during install. Proper torque on all bolts?

I will try to keep an eye on this thread as I am very interested to see the outcome...

Good Luck,

Bob.
Thanks for taking the time to answer Bob.

I already replaced the capacitors but I took the ECU back out just now and reinspected them. All is good.

I then had a suspicion that my AEM Truboost went bad again (already sent one back for replacement) so I just put an oscilloscope on the solenoid output and fed pressure into the gauge and the solenoid would not function. The waveform showed that the solenoid was getting power but as the controller tried to PWM the low-side, that voltage was only dropping a volt or so.

So, I suspected that I had a bad ground. Surely a bad ground would affect boost (via the solenoid driver) and the wideband reading and even the Apexi NEO since I have them all grounded together with a ring terminal at the ECU. I redid the wiring there, cut off the ring terminal and replaced it with a new one. Low and behold, the solenoid started working. So, I went out for a blast. Everything seemed good at cruise so I went WOT. First time it hit 15psi which is what I have it programmed to. Then on the second WOT run it went overboost and hit my 20psi warning limiter. Thinking it was a fluke I tried it again, same thing. DAMN IT!

Now I’m thinking that the boost issue might be a sticky solenoid, if it is stuck closed I only get wastegate pressure but if it stuck open the wastegates get no signal. Pretty sure that’s what’s going on with boost. Still have no idea why it is running lean when the boost is only 6psi though........something is still a mystery.

MJ
 

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Sounds like you got this issue on the run...

Hrmm...boost issues...running lean...I see one thing in common, AEM Truboost, AEM Wideband....

FWIW, I have always used SBC-iD boost controllers (in both of my cars, and my son's cars have run them too). I (we) have NEVER had issues (knock on wood).

Since I am not trying to win any drag races (just looking for a little more fun) I have never gone beyond the boost controller, set for 14ish PSI (I love these controllers for settings)....

You will solve this. Sorry I am do not have the expertise in your setup to offer what to check next...

Bob.
 

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A motor is essentially an air pump, and its' efficiency is determined by how much air (and fuel mixture) it can pass through. More flow = more power.
A naturally aspirated engine can pass air through at maximum atmospheric pressure, while "boost" measures the amount of pressure beyond atmospheric being force-fed into the intake.
More air (and more fuel to keep the mixture proportional) means more potent combustion and more power.
snaptube vidmate
 

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A motor is essentially an air pump, and its' efficiency is determined by how much air (and fuel mixture) it can pass through. More flow = more power.
A naturally aspirated engine can pass air through at maximum atmospheric pressure, while "boost" measures the amount of pressure beyond atmospheric being force-fed into the intake.
More air (and more fuel to keep the mixture proportional) means more potent combustion and more power.
Where are you guys coming from?
You read the initial post and then post CRAP that can't help at all...

Thanks for ENGINE 101. Please try to be a bit more helpful next time...
 

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Discussion Starter #8
Problem solved: was a malfunctioning AEM Truboost-X boost controller. It was intermittently keeping the boost solenoid in either the venting state or the closed state. This explains why I was either getting wastegate boost only or max boost with a lean condition.
 

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Awesome!!
Are you sure you didn't find your solution from
stevenmax0203
?

OMG.

Bob.
 

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Discussion Starter #10
Awesome!!
Are you sure you didn't find your solution from
stevenmax0203
?

OMG.

Bob.
LOL, I guess he was trying to help BUT I'm not sure what his point was. At least I solved it. Boy was it a freaking challenge. I've now had three bad AEM Truboost-X boost controllers. I've figured out what is wrong with the design, they use an "intelligent" MOSFET to control the boost solenoid that is supposed to be protected against overtemperature, overvoltage, overcurrent, etc.. It looks like the flyback from the solenoid coil is killing the device. I replaced it with a more robust FET (transistor) without all of the fancy crap and put a clamp diode across the solenoid coil to address flyback and wala........works like a charm. (Yes, I'm also an electrical engineer)
 

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Retired Software Engineer here, with just enough electrical/electronic knowledge to make me dangerous :)

Thank you for taking the time to post your solution. It will be helpful to others...

Bob.
 

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Discussion Starter #12
Retired Software Engineer here, with just enough electrical/electronic knowledge to make me dangerous :)

Thank you for taking the time to post your solution. It will be helpful to others...

Bob.
My pleasure. Thank you for your input.

Mark
 
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