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This has been an ongoing problem that has seemingly run me dry of possible solutions. I have a VPC (B chip) and AFR on a '94 SP60 6 speed. Basically the car is completely untunable because once we make any modifications on the VPC and AFR, the A/F changes a short time later.

I noticed that Lance at Toymoto had connected the VPC a little differently than the mkiv tech article stated that the vpc should be spliced into the wires on the ECU (I don't have a harness) [I cant get the exact colors of the wires because mkiv is down for some reason right now]. I think the wire from the VPC was yellow. Anyhow, the ECU wire that the yellow VPC wire should have been spliced into was cut and the end from whatever sensor that it was receiving a signal from was left undone. I tried splicing it like the mkiv tech article stated, but unfortunately it did not solve any of my problems.

I have heard a number of different proposals as to what was causing this.

One such proposal was that splicing an AFR into the harness instead of using a GCC can cause interference and prevent the VPC from operating correctly.

Grant thinks that it could be the result of a malfunctioning throttle position sensor (Those engine codes were thrown once).

I thought that it could be the O2 sensor, but the car is terciometric (cant spell it, 14.7 a/f) while cruising. This would also seem to rule out a malfunctioning FJO unit.

I have heard of some single's going lean in the midrange when the stock fuel pump is left in the 9/12v mode. Apparently some people have solved this problem by hardwiring the fuel pump to 12v. I will be trying this tomorrow, however, the car was previously wired to 18v (B&M power plus) and all that did was cause the car to go extremely lean on long trips (possibly by overheating the fuel pump). I later removed the B&M unit and the problem only happens now on even longer duration trips. I will probably be getting dual walbro's in an effort to eliminate any possibility of the fuel pump being the weak link.

I am really at a loss here. Lance at Toyomoto was the one who I paid to complete the install and get the car running right; however, he failed on a number of things (crummy boost source for EBC/wastegate [fixed by me and Grant], wrong settings on AFR [fixed by me and Grant], forgetting to bead the intercooler piping [fixed by Lance after I was stranded on I75], etc.).

I would really appreciate it if anyone had anything at all to offer.

Cheers.
 

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Jon, it's tough to diagnose a problem like yours over the internet. First things first, make sure your electronics are hooked up right. Make sure the splicing/wiring is done right, i have actually heard of MANY ppl having problems with the VPC when wired in rather than harnessed. I am also a believer that there may be some problems with interference due to splicing, but i do not have any proof... Let us know if you work the problem out...
Peter
 

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Peter,

Actually the car threw a Turbo Pressure Sensor code and stalled at the same time. Lance on the list pointed out that the TPS has the same power as the other TPS. I tested the idle wire (11v at idle, 0v otherwise. Actually I might have that backwards...) and the other wire for position sensing (ranges from .5v to 3.6v from close throttle to WOT). I know there is nothing wrong with the turbo pressure sensor because a bad turbo sensor would not make the car stall, it would just throw a code.

The throttle sensor seems to be getting the correct power, but its hard to tell as the car's symptoms are sporatic. Whenever we test it, it seems to be idling find at ~14.7, so its no surprise that it looks correct when it is actually working. Sometimes it idles in the 10s, but we never have a multimeter handy then.

I know its not the O2 sensor because the ECU is not capable of adding enough fuel to get it to idle that rich. When its idles 10.5:1, I have to take out 44% of fuel on the AFR to get it back to 14.7, which is way more of a correction factor than the ECU can provide.

The car's a/f is undoubtably completely FUBAR at part throttle. Its usually very lean, and the turbo doesn't spool well at all. Sometimes we can get it just right, and it will drive awesome. But that will only last for a few hours.

Peter, hopefully Oolan Zimmer will respond to this post, as I'm sure he knows a thing or two about spliced wires and voltage drops.
 
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Discussion Starter #4
Grant,

The car was idling again at 10.0 on the way back from your place tonight. My car is definatly fickle.

I've checked all the splicing and it seems alright.

The car is now hardwired to 12v. It was driving fine on the way back from Grant's place, but that could change at any moment. I will be sure to keep everyone updated.

Anyone have anymore suggestions?

Thanks.
 

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What injectors are you running???? If you are running 720's with a 720 chip, then something is way off kilter that is fucking the a/f up. Ever thought about checking your coolant temp. sensor???
If you are running 850's with a 720cc chip, you will have to spend lots of time tuning it out. You'll have to find a happy medium b/w idle and 3k rpm. Potentially, if you fix the problem at idle, it'll run lean from 2-3k rpm, if you fix the lean spot at 2-3k rpm, then you'll run rich at idle.
As for the turbo pressure sensor code... There are several possibilities...
I'm just thinking out loud and these are the ideas that are in my head...
Peter
 
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Discussion Starter #6
HT,

I am running stock injectors with the chip for a small single with stock injectors.

Why are you getting new springs and retainers?

Thanks.
 

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car - i am putting in titanium springs/retainers b/c i plan to rev my new car to 8000 rpm... More of a safety issue than anything else...
 

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Jon,

Why not change the VPC chip? sounds like you have tried everything else. $90 bucks for a chip might cure you problem. I heard that those quality control on the chips suck. I notice on my car no matter what I do to the change the a/f at 11 psi boost, the car always run rich 10.5:1. Now if i turn the boost up to 18 psi, the car runs 11.9:1. Moral of the story is, don't crank the boost ;) If you have the vpc installed like the mkiv site then u should be good to go. I would honestly look at your a/f at wot and at the most boost u feel comfortable to run. I don't have any idle problems. I used the afr to take out 8 percent before my cam gear was tuned. That made me 14.7 stoichmetric. When I put adjusted the cam gear it went to 13.9:1 and i had to take out a total of 14% to bring her back to 14.7.

Sid
 

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I believe the 18B VPC PROM is for a single with 720cc injectors and stock cams. I'm running it with an SP57, SP-Fuel w 750cc injectors and an SAFC. Everything is currently set to 0 with the exception of the idle response on the VPC which is 2 clicks right but that is just to adjust the throttle response coming off idle.

I've got an FJO wideband O2 in the car and everything runs as expected. At other than high throttle settings under boost the factory ECU works to hold 14.7 AFR and does it pretty well. Note: when you close the throttle at speed, AFR goes full lean (19.9 on the FJO). Under open loop conditions ie high throttle and boost, the AFR goes into the low to mid 10s rising to just under 11 at redline. All the educated comments I've read says this is how it should behave.

I also did a quick test and found even at high rpm (>5k in 1st and 2nd on my auto) with light throttle, the ECU still wants to maintain 14.7. Only under open loop does it do anything else.

If you're tuning with the AFR at <4k rpm, I think you're fighting the ECU's learning functionality. Even if you only tune >4k, if you run the car in that rpm range at other than WOT, you're fighting the ECU learning. I went with the SAFC due to it's hi-lo throttle mapping that I think will let me modify only the open loop behavior so I'm not fighting the ECU. I haven't had time to actually tune it yet though so this is "educated" speculation at best.

BTW, with the 18B, I get a nice stable idle at 14.7 AFR and excellant drivability as long as I put the 2 clicks in on the VPC response which takes out a minor initial stumble coming off idle. Due to an initial defective 18B PROM, I ran with the 18C (single, 720 cc, cams) and it idled poorly and would want to die when putting it in drive or returning to an idle.

I hope to put my theories to the test this weekend and do some street pulls with datalogging on the FJO and then adjust the SAFC appropriately. I plan on setting the low throttle point to over 90% to prevent any corrections under lower throttle openings and adjust only from 3.5k or 4k rpms up. You can check back with me to see if that keeps my AFR behavior consistent.
 
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Discussion Starter #12
I had the same problem with the B chip. Let me guess, all the lights on the VPC are lit up? Mine ran like yours and all the lights on the VPC were on all the time. Switched chips and its all better.
 
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Ummm, I didn't know that the lights weren't supposed to be lit up.

I've richened everything up 30 percent until my A chip arrives tomorrow.

I'll let everyone know how things pan out. Thanks to everyone who has helped me out.

Cheers
 
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After richening everything up from 30 - 42 percent, the car was running a lot better. So much better that it blew either the cam seals or crank seal (I hope). There is oil all over my engine bay. Smoke was billowing from the back of my car as the oil was vaporizing when it hit my exhaust. I filled the car back up with oil to try and limp to a gas station. My car is now sitting inoperable at the Toyota dealership. I figure that since I just had the seals replaced by them they will be happy to redo that, along with the timing belt, and serpentine belt since they have also been doused with oil.

I hope it’s just the seals and not the head or some other vital engine component.

My A Chip arrives tomorrow morning, I can't wait! Hehe... :/

I'll keep you all updated.

Thanks again for all your help.
 

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So does anyone know what the heck are all those lights for? I am stilling trying to figure that out :)

Jon,
Glad to see my guess was right.. See that anyone can be a tuner these days ;) Please follow up and post what seal when out. For you sake, I hope it is just the cam seals and nothing major. When was the last time you did your timing belt? Jarrett ,PHR, had my afr set to put ~43% more fuel from 2k to 6k rpm. He did this on 2+ psi boost. I didn't have any seals shot. I don't think that could have caused you to blow on of your seals. I drove 500 miles like that. Lar or someone can probably answer why if u find out what seal.

Sid
 
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According to some stuff I have read and what Toyota is saying, my removal of the vaccume hoses that are connected to the crank case has cause a buildup in pressure which subsequently blew out the seals.

I am working on getting Toyota to warrenty their work, that's my major concern. Also the rear main seal appears to be leaking, so it looks like I may be doing that at some point as well... I really don't care if they are leaking, I only care if they prevent me from driving my car, like last night. I have a video but need to find a way to digitize it. It is truely harrowing.

Does anyone have anything to say about this happening with the crank case venting to the atonesphere? Is it really necessary to have a vaccume source hooked up to the crankcase to prevent this from occuring?
 

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If you are talking about the lights on the front of the VPC, they are i believe indicators of how much a GCC is changing the simulated MAF input to the ECU. On my car running the VPC/AFC combo, the orange light is lit and the first green light is also, if i remember correctly. All of the others dont light at all..




sidwin said:
So does anyone know what the heck are all those lights for? I am stilling trying to figure that out :)
 
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