T2 swap runs bad when not in boost
 

I just did an S5 T2 swap on my s4 n/a. I'm running an S4 TB and TPS with S5 injectors, bypassed the fuel resistor pack, walbro fuel pump, no fuel pressure soleniod, no emisions, no omp.

The car runs awesome in boost, pulls really good, plenty of power. When I'm not in boost though it runs like shit. if I'm driving through a parking lot or something slow it will buck really bad and it makes it a pain in the ass to take off because I have to give it more gas then I should to take off or it will start bucking and sometimes almost stall.

As soon as I hit boost however it's fine. It doesn't matter what rpm's. I can be at 2k and get on the gas and it will kind of stumble then hit boost and be fine, or I can be cruising at like 70 and if I let off the gas and then hit it again it will stumble until it gets back into boost.

I thought it was a vac leak but I can't find one. It also idles good about three quarters of the time, a little high, 1100ish, and then the other quarter of the time it will drop to about 500 then catch and go up to 1100 and just keep going up and down like it's searching. I'm going to test the TPS as soon as I get the tool.

So what do you guys think I should try next? I've been daily driving the car for about 2 months since I finished it and it's doing great except for this problem. Thanks in advance for any help.

Which ECU? So far sounds like you probably have the wrong match between ECU and TPS, if nothing else.

Is your chassis high or low imp injectors? I believe s4 has a resistor box, and s5 does not for the injectors.

It's the s4 t2 ecu. Can't think of the number off the top of my head. And it's a s4 TPS so they match. I have s5 injectors so I bypassed the resistor pack. That's what like 5 diffrent people on here told me to do.

I forgot to put in the first post that I did the TB mod and am running an open downpipe for now until I can afford an exaust. Don't know if any of that would make a diffrence.

I drove the car for the first time in a few days and it's not really bucking as much, it almost seems like maybe it's running lean or something before it hits boost, it just doesn't sound right. Still stumbles bad when I let off the gas then get on it again. Maybe I'm just getting use to how it acts at low speeds so it doesn't seem as bad, I let my friend drive it and it was bucking pretty bad and he had a hard time taking off. Once it's in boost I think it's running pretty rich, if I let off the gas it holds a flame out the downpipe.

Just out of Curiosity,I would check the Injector Connectors.
If they are loose that would explain the Problem of Intermittent stumbling.
I had a loose connector on my car and I tell ya,It was a pain in the ass.
I happened to lift the Harness one day and the car smoothed out,..AH-HA!,I said!!!..I found it!

Just speed all the time.



How are the plugs? Timing set properly?

subscribed, my s4 tII is doing something similar.

Check the fuel pressure according to spec as maybe you're getting too much when not in boost. Just a thought!

The connectors on the injectors are good and tight. I put brand new plugs in when I did the swap but I'll pull them out tomorrow and check them. How do I check the fuel pressure? And can I find the correct pressure in the FSM?

The spec data is in the FSM and the process involves placing a gauge inline between the filter and the motor (send line). You take the reading w/engine running and w/key to on and the fuel check connector jumpered.

If the fuel pressure regulator vacuum line is referenced properly, the fuel pressure won't drop correctly when the engine is in low-load situations, causing an excess of fuel, possible causing the problems mentioned above. Having the vacuum line to the wrong nipple on the UIM could do this.

Best bet is to check both. Test as described above. Expect ~39 psi engine off, ~31 or so psi engine running.

Which nipple on the UIM is it suppose to go to? I have it going to the one on the inside of the UIM kind of above the primary injectors. Where the 2 nipples kind of point at eachother.

I took a look at it today and tried to find a vac leak again and couldn't. Pulled the UIM off again and cleaned even more where the gasket goes betweein the UIM and LIM. Then I decided to see if it ran any better with the TPS unplugged. It ran about the same but when I went to plug it back in I noticed the prongs on it looked kind of corroded. So I took a flat head screw driver and scraped them a lttile bit to try to get some of it off. Now when I plug the TPS in the idle bounces and I can't rev.

I'm thinking the TPS is way off and maybe it just wasn't getting a good, or any, connection at all before. I'm going to my friends house later to test it and put it in spec. I'll let you guys know what happens...

So i went to adjust my TPS and it turns out it was stuck all the way shut. A little wiggleing around and it opens and closes fine. According to what I read it's suppose to be 1k ohms closed at go to 4k at WOT. Now when I had it closed it read ~1.030 and at WOT it read ~.500? How can it be lower at WOT?

I did get it to run a lot better though after freeing up the TPS and setting it correctly when it's closed. It was way easier to take off and just barleyyy hesitated if I let off the gas and got back on it.

Then I went to drive it again a few hours later and it ran like shit again. Thought it was just cause it was cold but even once it warmed up and I did some spirited driving it still ran like shit out of boost and wouldn't idle. I adjusted it some without the meter to where it seemed to run better when I first did it. It was like all the way in and about 2 turns out so maybe I should have left it alone. I'm going to put it to where it's suppose to be again tomorrow and see what happens.

I messed with the TPS some more today. I put it back to stock setting and it ran ok. I started to think though that since my car is open downpipe and other stuff that might effect how the TPS reads that I might not want it stock. So I turned it from about 1.000 to .750 and it was running really good. It got pretty warm from testing it so much, I would adjust it take it around the block, open it up a bit, bring it back and let it idle for a min or so to let the turbo cool off, and shut it off to adjust some more. Did that about 8 times. So now when I drive it normally and it's just regular operating temp it stumbles a little. I'm thinking once I get a thermostat it will make the car run a little warmer and run better, if not I'll adjust the TPS again.

So can anyone tell me why the TPS reading drops when at WOT when it's suppose to go up? My car still runs like shit until I've been driving it for about 20 min and even then it's not perfect.

If you're measuring ohms, the reading drops when the measurement is taken between the Green/Red wire and the Brown wire while the ohms reading rises when measuring between the Green/Red wire and the Black wire. The voltage should rise from 1 volt at idle position to 4.5 volts on the Green/Red wire when the TPS fully extends.

Well I'm not really sure what I'm measuring it in... My friend who owns the multimeter set it for me. It reads 1.000 not 1000. Is that right? And in your opinion should the TPS still be in the stock position if I the car isn't completely stock? I also have the TB mod done. Didn't mention that before I don't think. Not that it should make a difference for this problem.

Also, I think I tested it on the green wire and the black wire(maybe it was brown) That's how it said to do it on fc3spro.

So a little update. My car still runs like shit. My friend said it might be a bad pressure sensor so I unplugged it and it ran the same. So I thought mine was bad and put on another one I had laying around and nothing happened. Then I thought it might be the coolant temp sensor for the ecu since I had broken the clip and wired a new one in. Thought maybe I had wired it backwards or something. So I tried it the other way around and nothing, then tried it unplugged completely and it still runs the same.

It's like no matter what I do nothing changes how it runs. I also finally installed a O2 sensor cause I haven't had one since I finished the swap and it didn't do anything either.

I don't know what else to do. I'm hopefully buying a wideband and SAFC soon so maybe I can figure it out then. In the meantime anyone have any other ideas?

Oh and when I test my TPS with the multimeter it starts at 1.000 then sweeps to I think ~5.000 but around 3.500 the multimeter says 0.L. Could my TPS be bad?

Did you use the Harness off of the N/A car?,and lengthen it to run to the TPS?

N/A harness, didn't have to lengthen it. The TPS plugs in just fine.

get a new tps

So I put my friends code light that he made on my car and the only code it threw was the TPS which I already new was bad. I put a new one on and it still runs bad, what a surprise. It's a little better I think but still far from running good. I think next thing I'm going to try is MAF.

Also, when I did the swap i bypassed the fuel resister pack. I was told I was supposed to do that since I had s5 high impedence injectors, but now I'm wondering if since the ecu is from a s4 and probably meant for low impedence that could be messing something up. What do you guys think?

As far as the injectors go, the only reason the s4 is able to run low imp is because of the resistor pack. If you are running high imp injectors the resistor pack should be bypassed or removed. Did you actually check the resistance of the injectors w/ a multimeter?

All s4 ecu's see HI anyways.It is the resistor pack that makes LO injectors to read HI at the ECU.
....and the reason I asked about the harness is that I had to lengthen the.wires at the connector for the TPS..and when I did I accidentally switched the wires.
The car ran good at idle but then it would go to shit when you Punched it.