7mgte stumble HELP
 

i need your help again. i fixed the tps wiring and the tps is working perfect (as you will see in the video it shows how much throttle is open in volts).
itis a bone stock 1987 7mgte motor.
there is a hesitation, stumble, hiccup at around 2500 rpm.
it is running very rich and getting horriable milage.
if it is a cold motor it runs good for about 40 seconds then this stumble starts.
i have an inline walbro and a intank OE supra pump.

while driving it can rev above the biccup but if the throttle is barely cracked it accels like i am flooring it. when the speed catches up to how much the throttle is open it acts like there is a dead spot. and the throttle is like a switch between on or off.

if i rev it up and hold it at like 4k and let it off it revs down and almost dies or dies.
most i have boosted on that crap gauge is 4psi.
io have great vacuum.

video HELP
http://www.youtube.com/watch?v=vOdnP...ature=youtu.be

just compression tested it.
#1-145
2-145
3-145
4-145
5-145
6-135
also i dont have the factory boost sending unit hooked up. the wiring showed that it went to the gauge only.
what rpm does the stock trim start to boost?
when does the fuel up vsv open? it does not matter if the fpr has vac or not.

plugs gaped at .028

https://sphotos-b.xx.fbcdn.net/hphot...60576812_n.jpghttps://sphotos-b.xx.fbcdn.net/hphot...73052215_n.jpg

scratching my head

No diagnostic codes stored in the ECU? The CEL doesn't even come on for most of them so if you haven't checked then do so. There's a how to in the MKIII FAQ section.

no cel and nothing stored. so????
i am thinking it is a boost leak but cant find it.
do you think the video resembles a boost leak?
when i turn the steering wheel it does not idle up. the ps pressure switch is working and the lines are clear.

Something just hit me....


Why are you running a second fuel pump, inline with the stocker? I'm assuming they aren't plumbed parallel.

i put in a second pump (intank) because i was thinking that the inline walbro (up on the fender) was loosing suction due to it is higher than the tank. so i put it in there.
started the motor (with 1 pump going) let it warm up, then when the stumble hit i turned on the intank pump. there was no difference between 1 or 2 pumps going.

You're sitting in the front row of Trouble 101, waving your arms and shouting "Oh me! Me, me! Pick me!".

And I still can't imagine any reason on Earth why you'd run a second pump (much less an in line, in series with the stocker) on a stock setup. Shit, people run over 400hp on the stock pump without any issues. So, again, WHY are you running the second pump? Is it plumbed in series (I presume it is which is awful)? Is there a bypass to ensure that neither pump can cause a catastrophic failure or the other due to its own failure? Did you at some point delete the in tank pump completely and install an inline instead (you know that in tank pumps generally last longer and are more consistent as they're better cooled)?

This doesn't sound like an issue with the fuel pressure up VSV to me. Could be a failure of the fuel pump relay and resistor pack... Might try bypassing them to see if that helps. You're not going to be boosting enough to see any significant stumble from a boost leak at that RPM unless you've got a full fledged hole somewhere.

Personally, I'm suspicious of your inline fuel pump, the AFM, fuel pump resistor pack/relay and your spark plug gap may be too tight.

What other mods are you running?



EDIT: Please don't mistake me for having a negative or mean tone in any of this. I'm not a fan of that particular setup but it has its place... The Supra just doesn't have any significant deficiencies in the fuel system so I really can't see the point in adding another point of failure and extra complexity.

there never was a intank pump. the truck is a 1980 so there was just a draw tube that went down into the bottom of the tank. there was a mechanical fuel pump on the old motor. i am only running 1 pump at a time. the second one was just for a test.
i am just running the cor.
i have swapped out the afm and no difference. i think i am going to run new wires from the afm to the ece and see it that changes things like it did when i rewired the tps (a previous thread).
3" exhaust from the turbo back, no cat, everything else is stock.

it acted the same with the .028 gap as it did the .032 gap.
thanks for helping me troubleshoot this

D'oh.... I didn't remember that this was a swap. Please put your truck's details in your signature so people reading know what you're dealing with.

I would definitely check the AFM's wiring, especially if the TPS wiring was the fault in your last thread. Is the fuel pump resistor and relay in place? From what I recall, on the 7M's setup bypassing the fuel pressure up VSV would cause issues with warm starts and warm, low load performance so you may want to try running the vacuum line to bypass it for diagnostic purposes.

if i remember correctly i did not run the fuel pump relay or resistor.
http://www.cygnusx1.net/Supra/Librar...ection=FI&P=70
if i remember correctly i did not run them because i (at the time) only had the inline pump. and i read that it dropped down to like 6v or something like that so i just ran the cor.

i also got a bunch of info off of supracharged.com as well. i will check the volts going to the fuel pump during the stumble and see if they are 12v.

http://www.supracharged.com/tech/wiring/c1.shtml

i will go back over the wiring and let you know how i 100% wired it.

the fuel pump is running and wired correctly.
i found some real wiring diagrams specifically for the 87 7mgte. so i need to check my wiring and see where i missed something.
http://www.turboninjas.com/mk3supra/
feeling good about it now.
thx for the encouragement. i will let you all know what i find. thx

FYI, the absence of the resistor and relay for the fuel pump is a positive in troubleshooting this. The reduction in power to the pump that it provides at low loads isn't a negative and helps low load operation. If its absence were the problem though you'd know by checking with a wideband for an overly rich mixture. It will not hurt the fuel pump to leave it in place and no, it doesn't reduce the power to the pump to that significant of a degree... most of the negative commentary you see concerning that device comes from ignorance spread through old wives' tales or is misinterpretation from feedback from people who've had to tune after market engine management components around it... Sometimes it's just easier to delete. ;)

i have a feeling it is in the HAC.
when i have it connected, the tps at the ecu it is 2.8 k ohms.
when it is unplugged it is 4.8k ohms.
with it plugged in it runs worse and with it unplugged it runs like in the video. so?????????

there is 4.8 volts from the ecu going to the hac with the ign key on. as well to the tps and afm.
does anyone else know what their vta k ohms is with the hac connected?

my hac ohm measurements is
vc-p = .786 k ohm
vc-e2 = 2.89 k ohm
p-e2 = 3.67 k ohm

so the vc-p is not in spec. does anyone have one they can test and see what they get? i am using a 114 fluke digital meter

page 121
http://www.turboninjas.com/mk3supra/...-EFISystem.pdf

Try using a voltage divider/resistor network to bypass the HAC and see how the engine operates with a static signal. You'll want between 3 and 3.5v for sealevel.

See here for some more detailed instruction.

so my hac is reading 3.04 volts and i am at 6500 ft elevation.
would that sound about right for what it should be?
i am going to do another video and show you guys what i mean by when it acts worse with the hac connected.

there is NO difference if i unplug the O2 sensor. nothing.....?
if i unplug the tps or the afm it wont run for crap.

here is a video driving. notice at the end where it accels when i barely have the throttle cracked.....could that be my iacv sucking in air past the tb?
when i say it "bucks" it feels like as if you would pop the clutch or wot then let off. feels like it is going to break a u joint or motor mount

http://www.youtube.com/watch?v=eDLr4...ature=youtu.be

also i was thinking about the hac. as the altitude gets higher it tells the ecu there is less o2 so it reduces the amount of fuel sprayed (right?) so in theory if it is a lean fuel issue pluggin in the hac would farther confirm that due to it cutting the amount to be sprayed.
hopefully the fuel pressure gauge will get here within the next 2 days.
with the pressure gauge could i put it on before the fuel rail? basically just before the dampener or should i try it on the rail like off of the cold start inj?
i will probably try both just to see how it fluctuates

I'm stuck typing one-handed for a while so this will be brief.

If you supply the HAC input with a static signal for sea level and the car runs better the it's likely running a bit lean normally. HOWEVER, leaning out or enrichineng can also compensate for other issues such as bad timing (mech and ign). Just unplugging the HAC may put the ECU in a failsafe mode (just as far as the sensor in question's input is concerned) causing the ECU to add a little more fuel on top of the trim for sealevel. Use a resistor network to provide the ECU a true sealevel signal, it's only a matter of sticking two resistors in the harness connector.

O2 sensor won't make any difference except for after warm starts with it disconnected (you'll run rich) and during closed loop operation at normal operating temp.

Before the damper is the fuel rail. :dunno: If you're referring to the return then no, that's not a pressurized hose. Yes, use the CSI's port on the rail.

Have you tried another AFM?

i installed a fuel pressure gauge. with just the walbro running the fuel pressure before the dampener is crazy bouncy like 32-36. with both of the pumps running (walbro and in-tank pump) the constant pressure is 38 psi. and it goes up to 42 ish with higher rpms.
with just the intank pump running the pressure is constant 34 psi and up to 40 when revved.

yes, i have swapped out the afm for another and it acts the same. i wish i could swap it out for a tacoma inline afm (since i have one and they are a lot less touchy.
it sucks because i have not seen even 1 mk3 supra in my town of 30,000 people. would be nice if i did so i could invite them over for dinner and swap some parts out.....shit

Ok, so not the pump(s). The irregular pressure with one of the pumps off isn't surprising... I wouldn't leave them both in place.

Personally, I'd get a wideband and a MAFT Pro, install a GM IAT and MAP sensor, delete the KVAFM and HAC altogether and then see how well you can tune it.

I'll re-read the thread later to see what we've missed or what is still suspect.

thanks. i turned off the walbro and am just running the intank pump for the steady psi.

i just got done at checking the voltage at each ecu terminal at idle and when the problem starts. the only thing that changes drastically is the egr output to the vsv. it goes from 1.11v to 14v at 2200 rpm when the hesitation starts.

i am going to try and read a bunch on the egr system and see what i can find.

i am going to try and get this done SOON. i need this truck for my elk hunt that starts in a week. otherwise i have to do a ton of work on my ford (replace ball joints, starter, and flywheel) by then.

would a coil pack with a small crack from the edge of the metal underneath cause a problem like this? would the coil test ok if it were cracked?

the hac is working again. it reads 3.05 today and read 3.8 yesterday.

I told you how to eliminate the HAC as a suspect. The HAC is quite low on my list of suspects.

If the crack in the coil pack could either allow for an arc to ground OR allow moisture inside then yes, it could cause a stumble. If it's on the low voltage side it's unlikely to cause a significant problem but I suppose it's still possible. A picture might help. Filling in the crack with enamel may patch it long enough for you to go for a drive and see if that is the problem.

i did what you said and bought the resistors at radio shack and now the hac is giving me the correct volts to the ecu.
the cracks start at the edge of the metal on the bottom so i think even if i epoxied it, it would still be able to arch deeper in where the epoxy could not reach so i ordered some new coil packs to try....if they ever come in, they were to be here today so i dont know.
here r some videos of drive by's. when it bucks in the first video i am holding the petal steady. when it hesitates it does that with the petal steady and if i push down it is just like n the video of reving it by hand and it not going above the hesitation.
http://www.youtube.com/watch?v=RAVWI...ature=youtu.be
http://www.youtube.com/watch?v=XaZRQyf-lpQ&feature=plcp
when it is stumbling the petal is steady and on the drive back by the petal is steady and it just comes out of the stumble and accells fine.

it feels like when a carb has the float set wrong and it is starving the jets of fuel.

http://www.supramania.com/forums/att...2&d=1354680943
the cracks under 2 of the coils

Well, it seems minor but I've never cut up a coil pack to see how they're built.

I have had issues similar to what is in your video from just a hairline crack in the plastic stem of a spark plug boot, toward the top no less... So I wouldn't dismiss it as a possibility. I wasn't affected to the same degree but keep in mind that if it's the coil pack then there are two cylinders firing erratically, not just one.

coil packs made it a little better but still heavy stumble.
if the ground going from the metal coil pack bracket is not hooked up it runs just the same. then if i ground it, it still acts the same. i think i remember reading if it does not have a good ground it will not run right. so what am i missing????
i am testing the plug wires for a grounding crack issue now.

There's an internal ground in the igniter which is known to corrode and can cause these symptoms. There may be a writeup in the MKIII FAQ section which I think was written by Suprra_girl.

well the plug wires did not shock me so not the plug wires.

i am looking to see if i can find that faq but no luck yet

http://www.supramania.com/forums/att...2&d=1354751699
opened up the igniter and the ground is good and all is clean inside. the alum where the rubber gasket is is corroded but the ground is clean. i am going to extra ground the igniter to the body

just ran a ground just like the faq. so we will see. thanks for the link and all of the help...this will be fixed tonight so i will be checking the computer ever so often to see if anything shows up on the forum. other than that i will be out working on the truck

i installed a 20 ohm resistor and used a 25 ohm rheostat to make the voltage divider so i could adjust the volts going to the ecu from the hac sensor plug.
the idle changes as i change the volts from 2.8 to 3.8.
seems that when i turn it towards 2.8v the stumble is worse and when i turn it up towards 3.8 it is less noticiable but still there.
SO i am thinking it is something to do with the fuel injection for sure.
the tps readings at the ecu plugs (with it unplugged) are out of spec when the hac is plugged in and when the hac is unplugged it is perfect as it is at the tps.
so ......... and it runs better without the hac plugged in.
i have swapped out the tps and reset it in the past with a new one form az. it acts the same if i use either of the 2 tps sensors i have.

-ok so i just checked the tps at the ecu with it running.
-vta at idle is .48 volts
-the stumble starts at .74 volts. (also at 2500 rpm)
-once the stumble starts if i press down on the petal it increases in volts to the ecu up to ~3.7v.
-so i am back to thinking it is a boost/egr/vac leak or something like that.
when the throttle is depressed past the .74 v quickly to say 1.2v it revs up like no problem or stumble.
then when the rpms are still up if i rev it again it will rev like a normal engine. i can hear the bov once i let off of the petal and the throttle body is closed.
i plugged in my spare cps and pulled the fuel pump fuse. turned the ign on and put a spark plug in the end of the #1 plug wire and grounded it to the body. as i turned the spare cps gear the plug would spark the same time the injector would click/fire. so i know my wiring and ecu are seeing the cps signal and telling the injectors to fire and the coil as well.....

I hope it's just not coming across clearly, but the spark plug shouldn't be firing when the injector is open.... Not on the same cylinder anyway.

yea i hear you correct on the ign/injector timing. was a long night.
i plan on starting to work on it again here in a few weeks. i just needed a little break from pounding my head. thanks for the replys and if anyone has any suggestions they would be appreciated.

I understand having to take a break. I've got to drop the engine out of my MR-2 to work on some stuff but I dislocated a carpal bone in my wrist this summer and can't afford the surgery so working on my car's rather tough. I'm probably going to be retiring from the site soon.

that is a bummer. bodys are like cars, it really sucks when they dont work right or break.
hope you dont leave too soon....for my sake.