RB20 TPS / high rpm sputter problem

[tylerdunigan]

I thought I already made a thread on the sputtering a couple months ago, but can't find it anywhere. Like I said, with my RB20 in the higher RPM range (usually 4500-5000 and up) the car will start sputtering. Almost like a fuel cut/or small boost leak, but not exactly. There is a noticeable power loss, but if you stick through it, the car will keep climbing. Sometime it will happen and just sputter once or twice, and be clear the rest of the way out, while other times it sputters like crazy. Anyway, I've changed the spark plugs/checked the coils/if I turn the car to "on", I can hear all of the injectors firing. After doing a lot of reading, I've started to think the TPS could be going bad. I went out and bought a multimeter and when checking the signal wire, I am showing ~.01v. When I checked the actual power wire (with the red probe in terminal 1 and the black probe in terminal 3), I get a reading of -5.08. The FSM shows at idle throttle, I should get a reading of ~.5v. It also shows it should jump up to around 4v when you open the throttle, but I am getting no change at all. This is the plug I have been getting the reading from...

http://i17.photobucket.com/albums/b70/tylerdunigan/4e395486.jpg

I tried getting a reading from the other side of the TPS, shown here...

http://i17.photobucket.com/albums/b70/tylerdunigan/7195ab2f.jpg

but couldn't get a reading of anything, coming from those 3 prongs...no matter how I set the probes to it, it ALWAYS either read 0 or -0. A guy on a local forum is somewhat convinced that the .01v is still within specs, but I just don't see it when I should be getting around .5v, AND with it not changing at all when I manually open the throttle.

Any tips/ideas? I'm new with the whole multimeter stuff, and wiring in general. I've probably spent 5 hours the past two days, reading on how to use the thing and searching through my FSM. I'm really leaning towards the sensor being bad, but like I said, I'm new at this stuff. Any help is greatly appreciated.

[Sileighty_85]

I think you need to have the TPS connected so it can receive voltage from the car.

The TPS doesnt create voltage it alters it.

so plug it all up, get creative with trying to get contact with the wires.

I got sharp leads so i can poke through the wire, or you can poke it through the back of the connector.

[tylerdunigan]

Alright, I was actually just told that from someone else too. I will be trying that today after work. Thanks for the heads up!

[Rabboni]

Doing what sileighty said is the most reliable way to test the sensor and the wiring at the same time. Just back probe the wires through the connector while ignition is in the on position and check your voltages at closed throttle, and at WOT. They should be approximately .5 volts and 4.5 volts respectively. After that, slowly open the throttle while monitoring voltages. It should rise evenly, and proportionately to where throttle position is. If you notice any dead spots, or voltage spikes or general weirdness, then the tps has a dead spot and needs replacement.

[tylerdunigan]

Rechecked the voltage with everything hooked up. Here's how I had it...
http://i17.photobucket.com/albums/b70/tylerdunigan/1bd20ee3.jpg

Results with throttle at idle...
http://i17.photobucket.com/albums/b70/tylerdunigan/4719375a.jpg

Results with WOT...
http://i17.photobucket.com/albums/b70/tylerdunigan/d8e7e662.jpg

Besides the idle voltage being nearly double what it should be, everything seems to be good and the voltage changed at a good pace along with the throttle plate opening. Still need to check the resistance though and pull any codes from the ecu

*edit - just got the resistance results...
20k = .96
2000 = 958
200 = 1

[tylerdunigan]

Someone has pointed out to me that the fuel pump may be weak, since it only does it under load. If I have the clutch pressed in and rev it up, it's all normal...it only does the sputter at high rpm's, under boost. This will be my next area to work on. I am browsing different manufacturers to see what kind they offer, but I will be picking up a fuel pressure gauge shortly to have in the car. I need one anyways, so at least now I'll be able to make sure I'm not running too lean.

[GenPac]

IdleValve (http://www4.wave.co.nz/~lakewood/Skyline/ThrottleTPS.htm)

The idle voltage should be within the .45 - .55v range with continuity between the idle contacts.

[nickr1987]

I'm having the exact same problem. I was leaning towards knock sensor but haven't had time to check it out yet. Keep us updated if you figure it out.

[tylerdunigan]

I will be in the garage tomorrow, adjusting the sensor to get a better reading for idle throttle. Although, I'm not sure that's the problem since it happens onlynin the higher rpms. I will be checking out the coil packs again as well

[tylerdunigan]

Ok. So I adjusted the TPS last night to try to make the idle throttle voltage closer to where it should be (.5v). With the sensor twisted all the way, the closest I could get was .65v, which dropped my WOT voltage down to 4.2v. This did nothing besides mess up the throttle response very bad. I adjusted it back to where it was. I've got a fuel pressure gauge ordered which should be here Monday. So as of now, my next step is to install that and see if I'm losing pressure when boost kicks in. I'll keep you guys updated and any other feedback is appreciated

[tylerdunigan]

The gauge came in, but I am not sure if I will be using this one or not. It is a mechanical gauge, and is not backlit. It will only be installed inside temporarily, until I get an electrical gauge for a permanent one, but I forgot to pick up the fittings/fuel lines while I was at the parts store today. I did, however, pick up some new spark plugs. I have read where they need to be gapped at .8mm's, but my FSM is showing between 1.0-1.1mm's. Anybody know the purpose behind everyone saying gap them at .8? On a side not, nothing has really been changed on the car, but there have been a 2 or 3 days this week, where the car has ran perfect. It's becoming a hit or miss problem now, which I do not understand how. Plugs should be changed out on Thursday, so we will see if that fixes anything. Hopefully, I will have the fittings for the FP gauge by then as well. ......as always, updates will follow.

[Sileighty_85]

drop the plug gap down to a .026-.028 inch gap and see how that works out.

[tylerdunigan]

Just curious, but why gap them to that when the FSM shows around .040" (1.0-1.1mm)

[tylerdunigan]

Just an update, but I have fixed the car. It all started on a day after I filled the car up with gas, but when it didn't clear up on the next refill (or the next 6 or 7 for that matter), I just assumed it was coincidence. I don't know if I got bad gas, or if it just loosened up some gunk, but about a week ago, I decided to run some Gumout Regane in it, to clean out the fuel system and see if that was the problem. Within a matter of minutes, the car was running multiple times better, but still not quite right. I changed the spark plugs out last night, and everything is running great now, with ZERO misses at all. About 2 weeks ago, I was checking the resistance on the coilpacks AGAIN, just to double check, and decided to pull out a couple of plugs while I was there. They were bad, and looked fairly lean. I'm assuming whatever was clogged in the fuel system, was obviously causing me to lean out, and ruined the plugs. Anywho, just wanting to give an update for anyone having a similar situation...and hope my troubles could help you out. Again, the processes I tried were...

Tested voltage/resistance on the TPS
Adjusted the TPS to have idle position closer to spec (changed it back the next day...it was awful)
Checked the coilpacks by unplugging them while at idle. (all changed the rpm's drastically)
Checked the resistance on the coilpacks. All turned out to be about the same.
Bought a fuel pressure gauge to see if I was losing pressure under load (never installed though)
Ran Gumout Regane
Changed sparkplugs (gapped at 1.1mm)