New hesitation at part throttle on 420R

[KnifeySpoony]

Ugh, new problem... so did a trackday yesterday, no engine issues all day, though I was struggling with a leaky brake reservoir cap. Will have to make another thread for that issue. Driving back from Sonoma, started getting a severe hesitation at partial throttle - basically from 0-5% throttle, tip in feels normal, however it's like from 5-20% throttle, no fuel is being added, and the car hesitates severely/will not accelerate at all. If I keep gradually opening the throttle, once its gets past about 20% or so, then it's like it catches, I get a surge, then the rest of the throttle travel is normal. Car pulls hard and smooth to redline. When I get the hesitation, it's interesting in that if I keep the throttle depressed at that position, and press in the clutch, the revs do not climb at all as they normally would when the load is removed. Today I test drove around my neighborhood - when engine is cold it's not doing it at all. Even when the water got up to temp it wasn't doing it initially, but as I continued driving for more than 5-10min, it started up again consistently. No popping from exhaust. No smoke that I can tell. 

 

I checked the TPS (FWIW I'm on CC roller barrels) with easimap - idle voltage is correct, and it seems to be sweeping/responding normal with throttle. Jiggling wires to the TPS while connected did not show any voltage fluctuation. I swapped out the sparkplugs and no change. Plugs I ran yesterday seem to look OK but 2 of them look different than the other 2.

 

Any thoughts? Bad 02 sensor? Bad TPS? Something else?

Edited October 8, 2022 by KnifeySpoony

[ashyers]

Did you check the TPS when it was acting up? I had an issue with the TPS connector that would only raise its head when good and hot. If you can get a log when the car's acting up that could be helpful.

 

Edit: Is your ECU unlocked? If so you could set it to open loop to help determine if it's the lambda sensor.

 

This stuff is great for cleaning up connectors!!!!

 

https://caig.com/deoxit-d-series/

 

Andy

Edited October 9, 2022 by ashyers

[KnifeySpoony]

What were your tps symptoms?

[ashyers]

The TPS signal would bounce around as the connection went intermittent leading to wonky fueling. It was not as consistent as you describe, but it became worse with heat and different vibration levels (RPM's). I added an edit to my last post about the lambda sensor.

 

Andy

[sltous]

Adding my notes from Rocky Mountain Caterham on setting up TPS for roller barrels as a reference if useful.

WRNOT 608 - Roller Barrel Setup Ford Duratec Engine (1).pdf

[Croc]

Sounds like an extreme kangaroo throttle which is common in Caterham CSRs but the heat connection (i.e. only does it when warm) makes it different.  Sticky throttle mechanism in pedal box or at throttle bodies?

[speedwagon]

the tps is a variable resistor and sensitive to heat and almost always made by the cheapest bidder. In this case i would just change it, as it happened without you changing anything.  john

[KnifeySpoony]

Going to swap tps today thanks to a very generous forum member. Will report back. 

[KnifeySpoony]

TPS swapped thanks to @sltous - seems to have fixed this issue. Only did a short drive, but similar to my last neighborhood test drive that clearly elicited the issue. I think issue is solved. So it would seem that as the TPS got hot (remember on a RBTB car, it's attached directly to the roller barrels which are attached directly to the head, so it gets quite hot), it would malfunction over that part of its range. I don't know enough about how potentiometers work to explain that, but that's what I'm going with. Hopefully it was just a dud TPS and I won't have to replace every ~3k miles, but it may just be a hazard of being mounted to the rollers, as opposed to being more isolated on a plenum setup.

[ashyers]

Glad you got it sorted.

 

I keep a spare around since the nearest source for SBD iTB’s is in England. Hopefully yours is easier to obtain.

[MV8]

I found some pics of the titan roller barrel tps arrangement. It may sound silly, but you could provide some thermal isolation with scotch tape over the tip and around the shank of the stem and shoulder of the tps body. Much less conductive than brass. You could do the same for the mating surface of the tps. If you'd like something fancier, a 0.0625" shim of noryl would do.

 

A 3d printed key washer to rotate with the roller and a matching body shim would work and bring the tps out a 1/2 inch or so but that's a lot more trouble.

[KnifeySpoony]

Ugh, so this problem is NOT solved. I took the car out today for a pre-track-season shakedown (first real drive after new radiator install). The hesitation didn't start until driving for about 20-30min. Seems heat is involved somehow? but car was at full operating temp for a while before the symptom started up. Same exact behavior as before. Not sure what I need to look into next. Thinking I should invest in a wideband AFR and see what I can learn. 

[MV8]

It sounds like you know what the mixture is doing already. Is the fuel level kept low/just enough, circulating over and over with a return system, warming and foaming more with each pass through the system? If so, try carrying more fuel.

Are you data logging? The coolant temp sensor (CTS) maybe be out of tolerance or failing as an open (infinite resistance). There should be a temp/ohm chart for the sensor to compare to ambient for the cold value. You could plug in a resistor (that matches the hot value) after warm up and test run for hesitation. Before aftermarket ecus became affordable and info about oem ecus was not readily available, manipulating the CTS was an early, crude way of providing mixture adjustment with the addition of a low value resistor or potentiometer in series with the sensor.

[KnifeySpoony]

Update: new o2 sensor and problem seems solved. 

[KnifeySpoony]

Well..  It's kinda solved but now there's a new symptom. Now the 5-20% throttle range is smooth, but from 0-3%, ie initial tip-in there is hesitation/sputtering/misfire. And it does it immediately after starting even when cold. Car starts instantly and idles fine. Giving it verrry slight throttle will cause it to sputter/miss. More throttle and it revs fine. Interesting the drastic change in behavior with the new 02 sensor but not sure how to interpret. I'm thinking the 02 sensor isn't even active when the car is freshly started so I don't understand why the new sensor would cause this behavior. I'm going to triple check the TPS voltage, roller idle spacing, sparkplugs, etc.

[Dave W]

Try advancing the TPS the slightest amount, also check fuel pressure, may be too low for initial enrichment. 

[KnifeySpoony]

I tried unplugging the new sensor and the car runs exactly the same. So clearly my new 02 sensor is not doing anything. So it seems to me that either it's 1: sensor is DOA, 2: it's incompatible (it's a Bosch sensor that used to be included with r400/420R not the no-name sensor my kit came with), 3: the wiring from the sensor to the ECU has gone bad, or 4: the ECU has gone bad. 

 

Seems like sensor logging wouldn't be that valuable at this point. I suppose I should check wiring continuity; how to do this? Multimeter at sensor plug and at ECU plug? What pins go where? I could also put the OEM sensor back in and see if the behavior reverts or stays the same.

 

[sltous]

@KnifeySpoony have you checked in the ECU map to verify that the lambda is used for anything?  I think I took a look through my map (unlocked 9a4 with a custom map) and could not find anywhere it was actually being used after discovering my lambda sensor was totally mis-wired.  You could also double check the wiring based on this document: https://www.sbdmotorsport.co.uk/app/uploads/2020/11/Lambda_3_and_4_pin_Wiring_Instructions.pdf

 

I agree, I would imagine sensor logging likely won't tell you much about the lambda readings vs static easimap usage unless you find there is a wire that gets loose under road vibrations

[KnifeySpoony]

Thanks for the diagram. So I guess the lambda is self-powered? No need to check for proper voltage. Just check for wire continuity for signal and ground at the ECU plug? I haven't done any sleuthing in the ECU. However, the car used to run perfect with the OEM sensor for quite some time. So I can only assume it was functioning at one point.

[KnifeySpoony]

Did a trackday at Laguna yesterday - Once again the car was fine on track (new PR actually), however the part throttle issues have deteriorated significantly. It's extremely unpleasant/challenging to drive on the street at this point. It does it even when cold, and doesn't like to rev at all on light throttle in neutral; sputters and coughs bad. I checked the plugs again - they all look fine and all look the same- don't see anything obviously wet - does this mean it's NOT a misfire then? The most rearward cylinder exhaust primary is a little cooler than the other 3 but not cold. While idling (which is smooth, btw), I unplugged each coil plug one by one: the front three cylinders this produces an immediately rougher idle. Unplugging the rear cylinder created no change in idle, however revving is even worse. I swapped coil harness and no change. Swapped coils between 2 cylinders - same behavior. The picture is confusing me more and more... One thing that I noticed is that immediately coming off track with the car very hot, it runs fine around the paddock - However in stop and go traffic on the way home with equivalent water and oil temps, the car was almost undriveable. 

 

Any thoughts?