Finally have my rebuild up and running (coolant seal leak), but it still has a problem it was doing before the rebuild.

It's a JDM S5 13B turbo, swapped into a 90 convertible.

It still has the same bad bogging and even stalling if the throttle goes up with much of any quickness. Even bumping the RPMS from idle to 2k will cause it to bog and stall. It was doing this before rebuild and I thought I had found the cause in that my charge pipe to cold side coupler was splitting as I was dismantling things for teardown. I thought it had a small tear and my problem was a vacuum and pressure leak. That is not the case....or at least not from that spot.

I'm still bleeding the coolant so I haven't had much time to diagnose anything. What I did notice is that the engine idles better and has less of a problem when vacuum hose that feeds my OEM boost sensor as well as my AEM boost gauge is off the UIM. I use the nipple below the BAC with a tee to feed both OEM boost sensor as well as my aftermarket boost gauge. With that nipple free engine idled smooth at at touch over 1k RPM. When I put the hose on the nipple idle drops to just over stalling with some bouncing of the idle.

When time permits I'll start testing TPS, OEM boost sensor, AFM, etc. I'll create a diagram of my vacuum routing. Any thoughts on this would be appreciated.

 

Secondary throttle plates not opening like they should ? I'd think it has something to do with the throttle itself, at least thats where I'd look to start.

 

One inaccuracy. I do not have my OEM pressure/boost sensor routed from the UIM nipple under the BAC. That nipple feeds both OEM BOV and AEM boost gauge. The OEM pressure sensor is routed to/from the cold side turbo splitter, which also is routed to my MBC and then from that to my wastegate.

What I noticed today is that idle jumps up about 500RPM when I pull the hose off the UIM to BOV and the idle evens out. Also if I pull the hose off the OEM pressure sensor or unplug the pressure sensor there is no change in idle.

FSM says to hook up a pressure tester to 100mmHG, turn ignition switch and check voltage. Can I simply blow in the pressure sensor and read the voltmeter?

TPS testing:
Narrow: .8 as I go to WOT it will read once at 1.06 then go into OL and then pick up and have one reading of 6.4 where it will hold

Full: .661 closed and as it goes to WOT it will range up to 3.8, then go into OL and pick back up 4.43 and hold.

 

I doubt it's the throttle plates. I haven't made any changes to the TB so I doubt those have suddenly gone out of alignment or started sticking. But I'll probably be pulling my UIM to look over my vacuum routing so I'll check it once it is off.

 

Hope you get it fixed, I'm getting really close to the point of when ill be putting my engine together and dropping it in

 

^ Thanks it will be. I"m checking timing, pressure/boost sensor and playing around with some spare TPS tomorrow.

Being a turbo swapped into an N/A and using an N/A engine harness I have to extend my TPS wiring and harness to reach the N/A engine harness. In the past I've simply spliced and soldered longer wiring. Tomorrow I'm going to create a patch with harness on each end so that I can simply swap TPS rather than have to modify each TPS I want to use or test.

 

Morning bump, looking for some advice

 

The TPS should not go open circuit during any of its movement range. Not saying that it is the root cause of this problem, but it is a problem and should be fixed.

 

Did you try bypassing the fuel relay in the engine compartment?

 

This answers my question in the thread about my father's car and fuel issues. I'm going to be working on my car in a little bit.

Among other things on my car I'll check the same sorts of things I'm testing on his car. Fuel Pressure, fuel resistor relay.

I checked the Brown/White wire on my TPS and it's within 4-5v, though I don't remember the exact reading.

 

This is something I've always wondered. Every TPS I have ever tested show OL (open circuit) at some point in the range. Every time the narrow range will show the base reading with throttle closed/at idle. As I move the throttle it will take one reading with the low range. Then it will go into OL and pick back up with one single reading in WOT range. While the full range will have pretty smooth readings in the low range, get close to the high range, go into OL and pick back up with a single reading in the high range.

Out of curiousity I've tested my father's S5 N/A (albiet it is having fuel delivery problems) and his TPS shows the same behavior.

 

I believe the FSM backs up what i have said, also other threads.

My old TPS did what you described, and when i got a good as new/used one, no more open circuit at any range.

 

a tps is a potentiometer. same as a fuel level sender, and multiple other mechanisms. as the pick up sweeps across the different resistance valued keys, the voltage changes depending on the resistance of those keys. it should be smooth, usually ranging from .5v to 4.5v, roughly. sometimes, a certain key(s) will be more worn than the rest and be exhibited as a "flat spot" in the band. the clearest and best way to sweep a tps is with an oscilloscope. a dvom just doesn't give clear stable readings. it's too slow.

and just for future reference, OL is not open circuit. open circuit is displayed as a blank screen on the meter. OL means there is a reading, but the meter is incorrectly ranged to pick it up

 

I've narrowed down quite a bit. I had my pressure sensor feeding off the turbo cold-side. I switched the hose to the UIM front top fitting and that made a noticeable difference. Idle is a little loppy, but sits at a solid idle range.

I also found that my throttle cable had a whole lot of slack in it. I tightened that up and that made a big difference with the bogging down. It is almost non-existent now, but still there a little bit. When it does bog the little bit that it still does I always here an odd noise from the engine compartment. Might be OEM BOV, or a vac/pressure source, possibly throttle butterflies.

Tomorrow I'll have a helper so I can better listen for it. Still need to check my timing and a few other things.

Welfare does have a point about OL. My electronics instructor would be very disappointed that I did not see that also :P

 

Really? maybe I should just duck out of the 12v industry then, because I have been mistaken for years.

He should be testing it in continuity mode, if he is trying to get the condition of the pots, as it's more accurate than volts. If he IS testing in volts, your right.

If you are testing the condition of the TPS, do it in continuity (ohms) instead of volts so your meter doesn't need to "auto range" on you. Be sure the key is off when you do this.

Yes, an oscope or analog meter would be best, but most only have a DMM.

 

whether he's testing in cont. or not, OL is not open circuit.

 

OL would be infinite resistance in continuity.

Your telling me, that if i put my autoranging multimeter in cont. and put the negative lead on my chassis and hold the positive lead in the air, I won't see OL?

 

continuity, yes. open is displayed as OL, my bad. he was clearly testing voltage though.

 

When i read his post, I thought continuity, but your right as it does seem he is testing voltage.

Thats why a few posts up I suggested testing the TPS on cont. so it doesn't auto-range on him and blip OL for a second. Also, in cont. you are sure that it isn't auto-range change and that it's an actual dead spot in the TPS.

 

fair enough. i wasn't trying to question anyones ability here. was only trying to help. hope we didn't get off on the wrong foot

and i agree. sweeping a tps is best performed with the meter ranged in cont.