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Old 04-01-2002, 12:08 PM   #1
Jewbaru
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Default Strange MAP Sensor antics, and my boost controller. MY00+ Owners read

Ok, here's the long version.

My car: 2000 Impreza RS, Ludespeed Stage II Turbo kit with Stage III Intercooler. Greddy Profec A controlling boost, J&S watching timing, RRFPR and SX Regulater controlling fuel. A/F guage and aftermarket O2 tells me whats going on.

Clamping: Started with a 4.7v Zener, then went to a 5.1v Zener, now I'm running the Split Second Voltage Clamp V2.

With the 4.7, the car bucked pretty hard before getting on boost. The problem was traced to bad solder, so the contact between the MAP and Zener wasn't solid enough, and the voltage wasn't clamping correctly. Once it was repaired, a voltage check showed the Zener was clamping at ~3.8v, way to low. So, I went to Radio Shack and picked up some 5.1v Zeners. I installed them, and it showed they were clamping at 4.77, BUT they had a habit of spiking(the car would buck quickly, and the A/F guage would shoot super lean for a split second, then go back to normal). I installed the Profec A upped boost, and eventually contacted Tom about picking up a Voltage Clamp from him. I sent him a MO, he sent me the clamp and I installed it.

Tom said they were set for 4.85v which is the highest the ECU will accept from the MAP. I took it out for a test, and I was still getting spikes/fuel cut. I figured since it was riding the fine line, it might have been spiking just a little, but enough to cause fuel cut. So, I turned it down a little (the V2 clamp is adjustable), and did a full throttle, full boost run to check the clamp voltage, it was ~4.77. I drove around normally, and the clamp STILL spiked. It didn't as much as before, but I was still getting fuel cut. I pretty much gave up, and made it a habit to stay off boost unless I was going WOT.

Then another problem cropped up. The boost controller was spiking on the onset of boost. I caught a spike to 10psi(!) before it settled down to 6. This of course freaked me out, so I flipped the dip switch on the back that's supposed to prevent spikes, and tested it some more. It was still spiking, but only to ~7-8psi. I thought it might be the vacuum hose, so I rerouted all the hose to make sure the air was travelling the shortest path possible. I took it out again, but the spikes were still there. I went looking for some tougher hose, but no luck, I also didn't have much time to search since I was heading the Chicago in a week. I turned the boost down to the wastegate level, and took it easy.

Then, the worst happened. On my way to Chicago, I went WOT merging onto the highway, I looked at the boost guage, and noticed it was climbing past 5psi, it hit 7psi, and I let off. The wastegate looked like it didn't open. I drove along for a few miles, and went WOT again, the wastegate didn't open, and boost kept climbing. I thought it might be from the silencer in the muffler, maybe it was adding too much backpressure, and the wastegate wasn't working correctly. So, when I got to the Hotel, we dropped our stuff, and I pulled the silencer. I went WOT, and again, the wastegate didn't open. As I was driving around, I noticed I couldn't hear the stepper motor clicking under the hood. I thought it died, which might explain why the wastegate wasn't opening.

As we approached the Navy Peir, I could hear the stepper motor clicking again, but it sounded like it was clicking a little too fast, like it was set to actuator mode. I didn't want to take a chance, so while I was parked in the peir, I cut the hose going from the boost controller to the upper wastegate nipple. With the hose cut, the wastegate was connected to a vacuum line after the throttle plate, and the other end was vented. I did a WOT run, and the wastegate held tightly at 4psi.

I was driving thru the city, and I noticed something strange. There was no MAP spike, no fuel cut, nothing. At part throttle, and on boost, the car drove smoothly. I got a little more aggressive with the throttle, and got full boost at a touch over half throttle, and the MAP didn't spike, not once, not in the slightest. The A/F read normal the whole time. I was dumbfounded, and amazed, what was going on? I tested it more on the trip back, the CC usually caused enough boost to make the MAP spike, on the trip back, it didn't. Driving around town, not a single spike, with my cutting the hose, the problem is gone.

There you have it, I disconnect the boost controller, and the MAP stops spiking. What the hell is going on? Was the high heat of the hard working turbo causing fuel cut (remember, the EBC will keep the wastegate closed untill desired boost, and the turbo will be working MUCH harder to produce boost, even at part throttle)? Did the low TPS signal, and high MAP signal cause the ECU to get confused? Did the low ambient, and high manifold air temps cause confusion in the ECU? I honestly have no idea.

Anyone have any theories of their own?
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Old 04-01-2002, 12:57 PM   #2
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i am going to say it has something to do with the boost controller seeing as how once you disconnected it the car ran fine. Maybe it's causing more spikes then are appearnt.

jeremy
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Old 04-01-2002, 01:27 PM   #3
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What voltage is that clamp set to? I thought 4.8V was the max allowable and that the ECU cut fuel (what moron thought of that one?) at 4.85v.

I would think that the softer wastegate actuation might actually cause the MAP sensor to not freak out as much. I never got wild bucking in my car, but I had a slight hesitation upon going into boost now and then (usually accompanied by a small A/F drop to lean and then back up to rich).
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Old 04-01-2002, 01:38 PM   #4
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right now, it's set to around 4.77v. At 4.85 it didn't go into full fuel cut, it just spiked.
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Old 04-01-2002, 02:05 PM   #5
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So, just to clarify, you got the Split Second Voltage Clamp that is adjustable? I had had the SS VC that was non-adjustable, set to 4.8v, IIRC. They had told me that the adjustable one fluxuated voltage clamping dependent upon different weather circumstances and whatnot... maybe it's applicable here?
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Old 04-01-2002, 02:24 PM   #6
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possibly, but I haven't seen any signs of it fluxuating, it hasn't spiked once since I disconnected the boost controller. I'll check.
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Old 04-02-2002, 05:45 AM   #7
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Well,
I have a 5V SS clamp and I do not think I have any problems. I get a little detontation, but I do not think that has anything to do with the voltage. It is timing, I think. So my question is, what is wrong with a 5V clamp? 8Complex: I thought you had a 5V, that is the one you told me to get a while back .

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Old 04-02-2002, 01:16 PM   #8
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scootr - Yeah, they call it the 5v clamp, but it clamps lower. I think they mean that it's meant for a 5v MAP sensor when they call it that.
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Old 04-02-2002, 02:15 PM   #9
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Update:

Sunday it was cool outside, yesterday it was almost 70, today it's in the low 50s and wet out. No spikes at all, car is still running smoothly. I'm going to increase the boost on the deltagate, and see what happens.
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Old 04-02-2002, 04:08 PM   #10
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Joel - Cool deal. Good luck hope it's nice and smooth still.
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Old 04-02-2002, 09:39 PM   #11
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I ran mine flawlessly off the wastegate at 6psi on a 7psi spring...Only when I added my boost controller did the problems arise....When I get a new one I will do the same thing...Right off the wastegate...only this time no boost controller...and the wastegate will be a Tial.
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Old 04-02-2002, 09:57 PM   #12
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no creepgate????
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Old 04-04-2002, 12:49 PM   #13
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Update:

Well, I upped the boost alittle on the deltagate. It rose a whopping .5 psi!!! so needless to say, there was no difference in driving. Still no spikes. I'm going to try and up the boost more later.
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Old 04-05-2002, 12:05 PM   #14
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Update:

Got the wastegate set, 6psi, not a single spike. I pulled the codes I had (they were set for a while) last night, and one of them was a MAP HI code, as well as the usual catalytic efficiency code. I noticed another "strange" code as well. The rear O2 heater signal.

My car was one of the cars affected by the recall, but I never got it done because of the turbo, and I'm too cheap to buy a new one. However, this is the first time I've seen the heater code. Oddly enough, the EBC, J&S, Voltage Clamp and A/F guage are all pulling off of that 12v current. Kindof a heavy draw, yes, but the car didn't act funny, or did it? With the EBC disconnected, and turned off, the spikes stopped. Could the little extra draw from the EBC have caused the clamp to not function properly? Hmm...

Even tho the EBC was turned off, it still had a little draw to keep the stepper motor working, but it just runs a set loop so the wastegate works like there's nothing hooked up to it, so it's possible it draws less power when off, than on. Regardless, I unplugged the unit the other day, and will eventually totally disconnect it.
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Old 04-05-2002, 12:31 PM   #15
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Sorry to hear about all of your troubles Jewbaru. Good thing you found the catalyst your car not working properly. The EBC was gonna be the next buy on my list, not anymore though. After reading of this, and the GReddy was the one I wanted, I think i'll pass.

Right now, I'm just running off the wastegate on my turbo, which obviously isn't adjustable (i.e. internal wastegate), and to combat this I was gonna purchase an EBC. Maybe these things don't work as well on lower boost settings, as many of the WRX guys seem to love them.

Any reasons why you think your GReddy unit wasn't working properly?

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Old 04-05-2002, 01:09 PM   #16
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To tell the truth, I have no idea, it just went crazy on me.
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Old 04-05-2002, 02:11 PM   #17
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It's a recall on the sensors... no matter what, as long as it's there, they have to replace it. They should have no problem doing it even with the turbo on there.
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Old 04-05-2002, 02:43 PM   #18
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Quote:
Originally posted by 8Complex
It's a recall on the sensors... no matter what, as long as it's there, they have to replace it. They should have no problem doing it even with the turbo on there.
I thought the same thing, but they said because it wasn't located in the stock pipe, they couldn't do the recall. I'll try somewhere else then.
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