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5VZ boosted with URD Kit - loss of power at altitude with wide open throttle

3K views 19 replies 6 participants last post by  oatmeal769 
#1 ·
I originally installed my URD Fuel Upgrade kit in SoCal and then a Split-Second AFR calibrator on top of it. I was able to get some real gains in wide-open throttle / open loop tuning by enriching the mixture from the stock 14.7 : 1 down to about 11.5 or 12 : 1.
When I moved to Colorado, I re-tuned everything and ended up with a maximum enrichment in WOT/open loop of about 12.5 or 13:1.

Question :
When I have it floored out on the highway (as in passing another car at 80 MPH), and even at lower altitudes (Like 2,500 - 3,000 feet) I notice that the truck loses power and seems to retard itself. I have to back off the throttle a bit to get it to stop doing this. When I back off just a touch (and presumably return to closed loop) I actually gain power and the feeling of lope-ing is gone.
My LM1 tells me I'm smoothly moving from 14.7 : 1 down to about 13 : 1 but I start losing, rather than gaining power.
Map A is custom tuned by me.
Map B is all zeros.

Any ideas why this is? Everything I read is that I'd gain power (and did at sea-level) by enriching the mixture. Maybe I'm thinking of the wrong reason?
 
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#2 ·
When you go up in elevation, you should get richer, using the same tune. There's less air, but same fuel, thus richer. When we take our dirtbikes up to the mountains, we have to rejet leaner because of less dense air. So this does not make sense that you are running much leaner. Maybe you've got another problem like a failing fuel pump, or clogged fuel filter. Also a cat converter that's mostly clogged will behave like you are saying, losing power at high rpm.
 
#3 ·
Those symptoms sound like your knock sensor is retarding timing when you accelerate hard. Do you have a GM knock sensor installed yet? If not you probably need one. Here is a very detailed thread about GM knock sensors by Dick4x4: http://www.customtacos.com/forum/13-performance/184210-knock-sensor-anyone-use-ks46.html

The stock knock sensors pick up too much noise above about 7psi. If you have a obdII scan tool that can show timing you can watch the timing drop while accelerating. When timing retards your engine will run richer because the fuel isn't burned completely.
 
#4 ·
That's another good possibility. Before I was tuned, I made my truck knock pretty bad a couple times. This kills the knock sensor ironically enough. My current 01 5vz had 1 failing knock sensor and eventually threw a code but the timing would jump around crazy (when monitored with torque app and cheap Bluetooth dongle) with bad power. I just joined the two signal wires together at the ecu and am running a sensor in only one bank. I tune for 11.5 so plenty rich, and pull a little timing mid range where the 5vz like to ping most.

Kurt can you verify the gm sensor fit the 5vz?
 
#5 ·
I don't know what fits the 5VZ. Dick4x4 probably knows maybe he will see this and chime in. He posted this information:



"The SU1075 that is the one for the Pontiac Sunfire/ Chevrolet Cavalier. Designed to have a nominal frequency of 7.0Khz. Will work well for anything between 6.6Khz-7.4Khz.

The thread on the SU1075 is direct fit M12x1.25 but with a taper thread design. That is a good thing because as I said earlier, you don't want the bottom of the sensor to be touching the block. Because of that, the torque spec is very less critical in the assembly. You just have to be sure it's tight. (Ideal thread between 2/3-3/4 of all threads)

The SU1075 have a internal resistor the OEM Toyota doesn't have. (according of my personal analisys to the mtg graph) it should give the signal less amplitude (voltage). That could actually be a good thing as it would be close to the Toyota sensors range. GM sensors give usually quite higher voltage.

Based on that I would say SU1075 for
2RZ/3RZ: Good choice
5VZ: Very good choice (if the actual body fits in the allowed space)
3S-GTE: Good choice, but would be nice to confirm with the Toyota manual shop"
 
#6 ·
I hadn't thought of a fuel delivery issue. One thing that is perplexing is that it seems to happen intermittently. That would say that it could be a fuel issue. I will also say that when it's really hot outside, I can sometimes smell gasoline when I'm sitting at an intersection or at idle. I just replaced my fuel filter a couple months ago, and I detect no leaks. I think there's supposed to be some pressure ventilation or something going on in the fuel system, especially when it's hot and that could be what I smell.
Could it be injectors or fuel rail, etc?
 
#7 ·
Oh - Well, here's something that may also contribute to the smell of gas - I have a P0446 - Evaporative System Vent Control Circuit Malfunction CEL.
Question - could that have anything to do with my possible fueling issues also?
 
#13 ·
Is your boost line still hooked up to the FPR?
What? Where? LOL refresh my memory what's an FPR?
Figure out a way to monitor the live timing values.
I can run the truck and watch map-B. The perplexing thing is that it seems to be intermittent. Sometimes the truck pulls just fine in high gear / RPM / W.O.T
 
#9 ·
I'm also beginning to seriously consider how much the knock sensors contribute to fuel tip-in, rather ignition timing, on the boosted 5vz when it comes to high gear, low load pulls. For example: 5th gear, going up a hill with light acceleration. Whenever I drove the 5vz across the country, I would sometimes get a knock sensor code when going down a deep valley and transitioning into going up a hill (serious elevation changes).

Can confirm, as other threads have indicated that the knock sensors go bad on the 5vz because of boost. I replaced the harness and both knock sensors about two years ago, and I've been getting the P0325 on and off for about two weeks now. I find it funny that people started switching to the GM knock sensors out of cost, but I can obtain a Toyota one off of Ebay for no more than ten bucks. Now the GM ones seem to start around 30 bucks a pop, go figure.

At any rate, there's a bolt hole on the 5vz block right above the exhaust manifold on both sides where I'm considering externally mounting the knock sensors, as opposed to under the lower intake plenum in the v-channel. The user V'FN8 brought up this location in some thread about switching knock sensors.

Here's the graphs of the SU1075 that came up on Google: http://mtg-technologies.com/automotivesubpages/knock/SU1075.htm

I'll be digging into my truck soon, as I've go knock sensors to chase down.
Check your gas cap first for that EVAP code.
 
#10 ·
I'm also beginning to seriously consider how much the knock sensors contribute to fuel tip-in, rather ignition timing, on the boosted 5vz when it comes to high gear, low load pulls. For example: 5th gear, going up a hill with light acceleration. Whenever I drove the 5vz across the country, I would sometimes get a knock sensor code when going down a deep valley and transitioning into going up a hill (serious elevation changes).

Can confirm, as other threads have indicated that the knock sensors go bad on the 5vz because of boost. I replaced the harness and both knock sensors about two years ago, and I've been getting the P0325 on and off for about two weeks now. I find it funny that people started switching to the GM knock sensors out of cost, but I can obtain a Toyota one off of Ebay for no more than ten bucks. Now the GM ones seem to start around 30 bucks a pop, go figure.

At any rate, there's a bolt hole on the 5vz block right above the exhaust manifold on both sides where I'm considering externally mounting the knock sensors, as opposed to under the lower intake plenum in the v-channel. The user V'FN8 brought up this location in some thread about switching knock sensors.

Here's the graphs of the SU1075 that came up on Google: http://mtg-technologies.com/automotivesubpages/knock/SU1075.htm

I'll be digging into my truck soon, as I've go knock sensors to chase down.
Check your gas cap first for that EVAP code.
I think people use the GM sensor due to the frequency range they operate in is more "boost friendly" not because they are cheaper.
 
#11 ·
Actually, people switch to GM sensors because they are stronger by design. That information been confirmed by an engineer who works are Wells automotive who manufacture aftermarket sensors. Cost for replacement been a factor at the beginning to search for an alternative solution but once swapped you usually don't need to replace the GM sensors because they will hold the stronger frequency (same frenquencies but stronger) compared to the Toyota sensor.


The point that is very important is to use a sensor that will work in the same frequency the ECU is able to work with, otherwise it's pratically like disabling knock control function. Some people use random sensor and claim improved timing and performance. It's sure because the system is just not retarding timing so it's fun until it fails.


I did quite a lot of seach regarding that because I didn't want to use any sensor without knowing the impact of it. I documented my searhs in the post Kurt4726 quoted in a previous post: http://www.customtacos.com/forum/13-performance/184210-knock-sensor-anyone-use-ks46.html

@garetcurry : Even if mtg-technologies seems to be equipped to test sensors, their frequency tests and results are sometimes not what sensors manufacturers advertise as frequency range so it seems something is not right in their methodology or something. So I can't say what is wrong but something needs to be clarified.


All that being said, there is no reason knock system impact on afr numbers. Even more to the lean side if they would impact they should get it richer.
 
#16 ·
Before I threw a code for knock, I could watch timing values go from 21 to say 10 or 11 instantly. it would jump around a lot too. Now they're rock steady. If you can see live timing on stock ecu see if you notice anything similar. Stock knock sensors are a known failing point on boosted 5vzfe.

To have your fuel pressure rise with boost you need to hook your fuel pressure regulator or, FPR, to a boost source before the throttlebody.
 
#20 ·
If you can see live timing on stock ecu see if you notice anything similar. Stock knock sensors are a known failing point on boosted 5vzfe.

To have your fuel pressure rise with boost you need to hook your fuel pressure regulator or, FPR, to a boost source before the throttlebody.
Ok, I'll look at my timing as well when I get a chance to test - Summer has me swamped! Hopefully the first full week in August.
5vz regulator only get filtered air pre throttle body. It does not see vacuum.
It looks like I need to double check my hoses and where they're all connected. I think the supercharger made some changes to the stock routing, and it's written about in the owners manual, but it's been so long I could use a refresh.
Sure thing is if your fuel regulator is not reference to charge pipe to sens boost variation it would explain your problem very well. I don't know if 5VZ regulator is manifold reference to see vacuum when stock or charge pipe reference only like RZ engine but you should look at it first.
Again, looks like I need to double check my hose routings.


Also, be sure that EVAP "problem" is not causing unmetered air admission that could cause wrong reading from the MAF.
Yeah, I need to fix that stupid box too.
 
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