Pfc And Strange Ignition Retard Issue .

[discopotato03]

Hi all , I'm getting some strange timing retarding taking place at very small throttle openings .

I stumbled upon this today when looking at the logging moniter page and comparing it to the ignition timing table .

I suspect the TPS or its voltage output may be part of it . At closed throttle I think its voltage is about 0.041 and full throttle is around 4.1v .

Hot idle shows 15 degrees but at very small openings ie 0.43 to 0.45v sometimes the timing goes backwards to 10 or 11 but can fluctuate back to 6 or at least once 0 and it starts to hunt . Once the TPS voltage gets above about 0.55 volts everything seems to work ok .

Is this something Skylines do or is this some isolated issue ?

Thanks for any help , cheers A .

[The Dan]

Set the TPS to 0.55v

[rob82]

Im pretty sure PFC's have delta ignition control on the rb25's. I've seen this issue before on an s14 where it wasn't learning the closed throttle value so as you slight increased the revs by applying throttle it would reduce the timing to try to control the rpm. Once you get enough throttle on board it flicks over to the main timing map.

As elite said try a higher throttle value I wouldn't go above .55v though otherwise your idle strategies and decal fuel cut won't work.

[discopotato03]

This issue is weird because the TPS voltage climbs and falls reliably and always has the same min and max .

The issue occurs intermittently at around 1150 -1230 revs and sometimes it retards backwards by four to five degrees ie 10 - 11 and the fast idle (via accelerator) gets a bit unstable . Nothing in my timing table is less than 15 and no correction factors should be doing anything at normal running coolant temps . Sometimes it drops back to zero and not surprisingly goes a bit haywire with no load 1200 revs and 0 degrees timing .

I don't know if its related but the nock number fluctuates from 0-1 and occassionally 3 . It should not be knocking with Lambda ratios of 1.00-1.04 .

I've never touched a TPS on an RB so if someone knows the test/set process or can link a DIY I'd appreciate it .

Also how to get a PFC to relearn the new min max voltages PLZ .

I really would like to solve these niggling issues before going near a dyno and having problems that aren't tuning ones .

Thanks in advance , cheers Adrian .

One last are these S2 R33 TPSs a problem and sometimes need replacing ? Guesses not cheap .

[JonnoHR31]

Undo the screws and twist the TPS so that it reads .45v when the throttle is closed. The problem is your touching the throttle but the TPS voltage is still lower than the threshold required for the ECU to declare it open, so your feeding the motor more air (and in turn fuel) whilst the ECU is still in closed loop idle control, so it drops timing to try and drop the revs back to it's target idle (usually 750-850 rpm). Whilst in this closed loop mode the main ignition map is completely ignored, you could have 50 degrees of timing in the corresponding cells but it'll still idle around 15 (+/-5).

[discopotato03]

My PFC is set not to run in closed loop so all the std probe does , when the Datalogits not connected , is plug the hole .

I've been searching here and it seems occassionally people have TPS issues from guesses incorrect setting or failing units .

I looked up the part number for an ECR33 S2 and I believe its a Jecs part - number A22-661 . On EBay they go for a little less than $100 and I need to check out if any of the local vendors stock them . I've seen TPS units bugger up in either their idle or WOT switches or the variable resistor and send things awry drivability wise . I probably should buy a new one and regard it as a wearing part , one thing less to screw up .

I'll look for a test/reset DIY later .

Cheers A .

[The Dan]

Just test it with a multimeter......

Also the PFC has a T/POS voltage output on the settings>sensor chk screen

If it's at 0.4v then move it to 0.55 and see if it fixes your problem. The TPS is adjustable on the T/body. Just loosen the 2 bolts and turn it to get the desired voltage. Another method is to watch the TPS idle light in the settings. I had to set one at 0.35v the other day so a Nistune would recognise the thing was at idle on the TPS. I argued that the manual requests 0.4-0.6V but at the end of the day, that's what the car wanted and it ran better afterwards

[GTSBoy]

My PFC is set not to run in closed loop so all the std probe does , when the Datalogits not connected , is plug the hole .

Cheers A .

He did not mean closed loop mixture control. He meant (and in fact specifically said) closed loop idle control.

[discopotato03]

Fair enough I missed that point . Can I trust the Datalogits TPS voltage number at idle and adjust from there or do I have to probe the TPS plug wiring ?

If probing the TPS plug wiring which is the sensor one and earth ?

Thanks again , cheers Adrian .

[wolverine]

What figure does the commander or datalogit say Disco?

[JonnoHR31]

Fair enough I missed that point . Can I trust the Datalogits TPS voltage number at idle and adjust from there or do I have to probe the TPS plug wiring ?

If probing the TPS plug wiring which is the sensor one and earth ?

Thanks again , cheers Adrian .

Yes, the figures the PFC reads are fine (if they weren't these are the ones you need to make right anyway, regardless of what's happening at the plug). Just have a play around with the adjustment and see what works, I highly doubt you need to replace the whole unit.

[discopotato03]

From memory 0.41 at idle and 4 . something at WOT , I think I posted that above . I'll see if I can find Garys ear thisafternoon .

Interesting about the closed loop idle timing . I was reading that feller from Celica.orgs thread on Tuning Datalogit but sadly the Toyota Datalogit software has different options to the Skyline ones . They can turn off this idle timing control and if I could do that it would give the game away for certain .

It sounds logical that my TPS needs "advancing" up half a volt so the PFC can see the TP changes . Judging by the voltages on Datalogit I would have thought it would because the bad point is at around 0.43 volts (up from 0.41) but if its too low for the box to recognise then it probably thinks its trying to idle at 11-1200 revs and retards to pull it back . If I have it right the Datalogit guide mentions the scope for timing triming is 5 degrees either way so how mine turns 15 into 0 at times is anyones guess .

Anyway fingers crossed this works and like the coils is another unforseen prob this car could have had for some time .

A .

[The Dan]

Fair enough I missed that point . Can I trust the Datalogits TPS voltage number at idle and adjust from there or do I have to probe the TPS plug wiring ?

If probing the TPS plug wiring which is the sensor one and earth ?

Thanks again , cheers Adrian .

The pfc readout is fine but using a multimeter is easy too. Signal wire is the centre one. You can easily find power and earth so I don't need to explain that.

If not sure, just find 5v, then check the one next to it, it should be 0.4x or whatever it's set to at TPS closed

[discopotato03]

Moving the TPS makes no difference between 0.41v and 5.2 volts , at a certain speed the timing retards often back to zero and after the revs climb a bit jum up to 20 + .

Bigger fish to fry as I found a coolant leak in the turbos return line and I can't get at it behind the head . Its a HKS GTRS and where the braided lines barb meets rubber hose its leaking I think under a wormald screw clamp . After much screwing around it looks like all the heat shields around the turbo have to come off so the banjo fitting can be undone to pull the line high enough to get at the problem section . Great .

A .

[The Dan]

Did you mean 5.2v or 0.52v?

[discopotato03]

Sorry my bad , 0.52V . Something I did noticw was that the WOT voltage didn't rise with the increase in closed or base voltage if you like .

I would have thought that the whole range shoud have risen not just the base voltage at Idle .

Fixed the water leak , bastard of a job though .

A .

[discopotato03]

Does anyone know of any correction setting in a PFC which would retard the ignition timing to zero in the 11-1200 rev area and drop out at guesses 15-1600 plus revs ?

I increased the idle and FC numbers slightly and made each pair the same to see if I had things wrong way round but makes no difference .

I really need to know if this is my PFC screwing up or some other thing screwing it up .

A .

[t_revz]

Mine started doing this after work. Engine is 2200kms old. Just finished dialling in cams which were out. Has been fine til today. Started and ran fine after work but as I took off it was completely gutless and stalled. Had a few goes then revved it up to 1500 to get going. Every time I stopped it would be idle fine until I started to come off the clutch. I looked over and saw it showing 8 degrees one of the times but too hard to keep looking while it was happening.

At a guess I'd say its happening from idle to 1200. I usually take off without any throttle and its fine but not tonight.

Couldn't see anything strange while driving. Will check tps voltage tomorrow but I previously had it at .43v

[discopotato03]

I don't get it as much for some reason with lower ethanol concentrations and I think redoing the idle learn helps .

If you check your TPS can you check that the voltage increases/decreases and that the idle contacts open/close properly - assumes S2 type dual TPS .

Cheers A .

[t_revz]

I have s1

.43-.45 pedal released. Increases smoothly. I didn't remove sensor from throttle body during rebuild so still in stock position.

What triggers idle map? Below a certain voltage and anything else?

Strange that I have taken off hundreds if not thousands of times without any throttle yet last night at 1000rpm and easing the clutch I couldn't even move.