7mgte stumble HELP

[ccguy]

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.

[cre]

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.

[ccguy]

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

[cre]

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.

[ccguy]

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.

[ccguy]

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

[cre]

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.