4AGZE - No Boost... help?

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maxpham
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4AGZE - No Boost... help?

Postby maxpham » Sat Dec 21, 2013 11:54 am

Recently, I've had an issue with my 4AGZE not pushing out boost. I suspect that it's an ECU issue. I have replaced the fuel pump, fuel filter, and map sensor while diagnosing this problem. Manually triggering the supercharger's clutch shows positive pressure but at around 7psi there's a hint of knock and the ECU sends a fuel cut signal as indicated from a decrease in fuel pressure. I am using the stock ECU (smallport AE92 89661-12611 w/MAP&DLI), a Walbro 255lph fuel pump and a Tomei FPR. I didn't see any engine check lights but I'm going to see if there are any engine fault codes on it today.

Here's a video if it'll help:
http://www.youtube.com/watch?v=kUx0VSLE82s
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yoshimitsuspeed
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Re: 4AGZE - No Boost... help?

Postby yoshimitsuspeed » Sat Dec 21, 2013 1:13 pm

When you say a hint of knock do you mean detonation or do you mean it makes a thud or clunk kind of sound?
I assume you are running premium?
If it sounds like it's detonation the first thing I would do is try a higher octane gas or if you are running the highest possible try adding some toluene or octane booster. See if you can get rid of the knock and see if that allows you to make full boost.
If both problems go away then you just need to figure out why it's knocking.

Are you running a bigger pulley? Why the 255 and FPR?

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Re: 4AGZE - No Boost... help?

Postby maxpham » Sat Dec 21, 2013 2:31 pm

yoshimitsuspeed wrote:When you say a hint of knock do you mean detonation or do you mean it makes a thud or clunk kind of sound?
I assume you are running premium?
If it sounds like it's detonation the first thing I would do is try a higher octane gas or if you are running the highest possible try adding some toluene or octane booster. See if you can get rid of the knock and see if that allows you to make full boost.
If both problems go away then you just need to figure out why it's knocking.

Are you running a bigger pulley? Why the 255 and FPR?


It was hard to hear exactly with the s/c whine and engine revs but it was a pinging clunk. I am running 92 octane but will pickup some octane booster to see. The 255 and FPR are for future plans for the engine, which includes a bigger pulley once I get this GZE working properly. I appreciate the help yoshi.

I just checked and there is a fault code. It appears to be fault 21 which points to a fault in the O2 sensor. I'm going to remove it, verify the wiring, check for carbon, and replace. Kind of makes sense maybe.
http://www.youtube.com/watch?v=7N1_ivSc86o
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Re: 4AGZE - No Boost... help?

Postby maxpham » Sat Dec 21, 2013 11:10 pm

No joy... replaced the O2 sensor and checked other sensors and it's a bit of a mystery. Not sure what other input signals would make the ECU limit boost. I've reset it numerous times while tinkering. Any suggestions other than find a new ECU?

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Re: 4AGZE - No Boost... help?

Postby maxpham » Thu Dec 26, 2013 2:34 am

I've checked grounds on all the electrical components I can reach including those which I stuck behind the dash. This is perplexing. The engine doesn't sounds normal and it's not making any amount of positive pressure. Here's a startup video:

http://www.youtube.com/watch?v=ueHsIqyp8S4
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Re: 4AGZE - No Boost... help?

Postby yoshimitsuspeed » Fri Dec 27, 2013 2:21 pm

I would put a test light on the plug to the SC and see if it's cutting power when this happens or if it's staying powered and maybe slipping the clutch or something.

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Re: 4AGZE - No Boost... help?

Postby maxpham » Fri Dec 27, 2013 7:38 pm

No joy Yoshi. Did that a couple weeks ago at the shop and the SC never gets a signal to kick in. Manually triggering the clutch sends in boost but I'm questioning why the ECU doesn't want to trigger. My working theory up until now has been the ECU went limp. I replaced it with an AE101 4AGZE ECU and it's still not boosting. Could it be a bad air temp sensor?

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Re: 4AGZE - No Boost... help?

Postby yoshimitsuspeed » Fri Dec 27, 2013 7:56 pm

You say it makes 7 PSI but never gets any power?
Are you sure you are measuring it right.
It looks like the relay switches to ground so it should have power whenever the key is on. It should then switch to ground. If you get power you might check out the relay. You might also ohm out the stator.
I don't know of anything that would make the ECU cut boost. I don't think I have heard of any such thing.

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Re: 4AGZE - No Boost... help?

Postby maxpham » Fri Dec 27, 2013 9:32 pm

yoshimitsuspeed wrote:You say it makes 7 PSI but never gets any power?
Are you sure you are measuring it right.
It looks like the relay switches to ground so it should have power whenever the key is on. It should then switch to ground. If you get power you might check out the relay. You might also ohm out the stator.
I don't know of anything that would make the ECU cut boost. I don't think I have heard of any such thing.


It got 7psi when manually triggered, not by itself. Checked the relay and it had ~85Ω (p1,3). Voltage checks were sat on it as well. The ECU does not power the SMC.

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Re: 4AGZE - No Boost... help?

Postby yoshimitsuspeed » Sat Dec 28, 2013 11:41 am

maxpham wrote:
yoshimitsuspeed wrote:You say it makes 7 PSI but never gets any power?
Are you sure you are measuring it right.
It looks like the relay switches to ground so it should have power whenever the key is on. It should then switch to ground. If you get power you might check out the relay. You might also ohm out the stator.
I don't know of anything that would make the ECU cut boost. I don't think I have heard of any such thing.


It got 7psi when manually triggered, not by itself. Checked the relay and it had ~85Ω (p1,3). Voltage checks were sat on it as well. The ECU does not power the SMC.



So you tested before the relay and SMC output is not being triggered at all right?
And you checked for codes after replacing the O2?
I am much less familiar with the MAP GZE. Maybe it has a fuel cut system tied into the MAP similar to the 3SGTE's or something. Have you tested the MAP?
In the diagram above is the vacuum sensor the primary/only MAP or another pressure sensor of some sort?
Is that the proper manual for this motor? If so does it have anything in the troubleshooting sections in FI or SC related to not making boost? I bet your answer or at least some good pointers lie there if you can find them.

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