STUMBLE on acceleration!! Vid inside, tried everything

[mk2 supra]

So please read everything Ive done to diagnose this before you just throw out suggestions so were not wasting each others time, Im an auto tech and not a newb to cars, but not that familiar with the 7MGTE itself yet, so Im totally stumped. I still have yet to feel boost outta this thing and its real depressing after all this work...So first its an 88 7mgte--
the symptoms
It stumbles and bucks under any kind of decent acceleration, its load sensitive, not a specific RPM or throttle position, its well before it gets into boost, usually -10 in vacuum, its not a single cylinder but all of them, it doesn't smoke whatsoever, its a lean condition, u spray carb cleaner into a port and it wakes right up.
What Ive looked at to try and solve this and what can be ruled out
Fuel pressure- Ive driven with a gauge hooked up and gotten it to stumble, pressure doesn't drop at all
Fuel pressure regulator- pressure rises with MAP, I can unhook the vacuum signal and it still stumbles the same
CPS- Ive pulled it off countless times, as the vid will show Ive tried different ones, off of known running cars
Fuel injectors- They were cleaned/serviced/balanced at a reputable shop. and JUST IN CASE I picked up some shit from the tank before I pulled it out and cleaned it, I motorvac'd the injectors all clean again.
Check engine codes- Theres none
I pulled the fuel tank and cleaned everything
I unplug the AFM and trigger the CEL, still does it
Keep in mind this is an all redone engine and I went everywhere... so new plugs/wires, virtually everything reconditioned or replaced, and this was a running engine before the build/swap so its a big WTF. Ive taken my time on this all connections are soldered, all gauges work, Stock ecu, stock injectors, stock cams, stock AFM, BPUs. Im desperate for help, this thing has so much potential and its a gutless wonder that isn't even safe to drive, Thanks!!
http://www.youtube.com/watch?v=gW_3WlCd1SE

 

[RiyadYar]

have you checked for boost leaks

 

[suprra_girl]

What fuel pump are you using.
Where are you getting the vacuum source for the stock fpr

If it was a boost leak it would be running rich and blowing out black smoke particularly when throttling I would say.

 

[mk2 supra]

would it be a factor in this low of pressure? like I said negative 10 inches of vacuum is where does it now. when I first started driving it I might be able to get away with a pound or two of boost but its just gotten worse fast, like after seating the rings on the first drive no boost. also it's worse when the engine is cold and gets better as it warms up. I've been meaning to boost leak test it I haven't yet though, I thought for sure it was cps cause when I pulled mine to clean and regap it the problem got worse, so bought another one, same thing

 

[Poodles]

Could be TPS, bad timing, etc...

 

[mk2 supra]

What kind of timing do u mean? Ignition timing I did with a light when I first got it going, but not after changing cps. Cam timing SHOULD be right, is that a possibility? Thanks for clarifying on the boost leaks thats what I figured, this thing is clean as a whistle when it stumbles

 

[mk2 supra]

Could be TPS, bad timing, etc...

Even if its at different throttle positions? the big thing I'm torn on is I'm having trouble monitoring any sensors, I come from a DSM background where I can data log and monitor everything

 

[Poodles]

Cam timing could be off, and TPS is pretty easy to check through the procedure in the TSRM.

Have you tried checking for codes anyway? Not everything with light the check engine light.

 

[hvyman]

Have you tried another afm?

And ya the cel doesn't have to come on for there to be a code.

 

[RiyadYar]

You have to re time everytime you reinstall the cps

Sent from my SCH-I545 using Tapatalk 4 Beta

 

[Bmettie]

Look for cracks/tears in your accordion pipe. Under acceleration the engine under the hood is moving quite a bit and if theres a crack in the pipe then you'll suck in "unmeasure" air and stumble. I've seen it dozens of times.

 

[AJ'S 88NA]

My bet is on TPS needing adjustment, or timing, if you didn't time it with a light you should and with the jumper wire on which ever terminals the TSRM says in the Diagnostic box.

 

[mk2 supra]

What fuel pump are you using.
Where are you getting the vacuum source for the stock fpr

Inline walboro 255, all the EGR is deleted so its pretty short on vacuum lines, just that and my BOV pretty much. I know its a good source and show fuel pressure change with manifold pressure

Look for cracks/tears in your accordion pipe. Under acceleration the engine under the hood is moving quite a bit and if theres a crack in the pipe then you'll suck in "unmeasure" air and stumble. I've seen it dozens of times.

Its a good thought, but doesn't really apply here

and trust me guys... NO CODES! lol

 

[mk2 supra]

Update and moving along... I did this voltmeter check at the ECU
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=FI&P=49
and everything checks out great and in spec, which would include TPS.
I ignition timed it since I know this CPS can stay in now, but like I said its done this stumble since day 1 of the swap, when it was timed right but I understand you guys deal with a lot of obvious stuff and have to cover the bases... Also Ive seen the outside of the crank dampners sometimes move off of actual TDC and allow you to time it wrong, I tried a couple extremes but 10* is for sure where it likes it. Just know Ive spent months on this and tried not to overlook anything. Im in process of a BLT now, will let you know. Could it still be the AFM if it stumbles while its unplugged? Worse actually. All I see on testing it is THA-E2 pin resistance, which is ok. What else could we be missing??
Thanks

 

[AJ'S 88NA]

Checking and setting the TPS is two different things from what I've learned, have you done this http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=FI&P=101

 

[jetjock]

Tough without a scan tool ain't it? Well, figuratively speaking...

 

[mk2 supra]

Tough without a scan tool ain't it? Well, figuratively speaking...

YES!! lol.
Well after a boost leak test and messing around with a smoke tester in intake piping and everything, I found a post MAF intake leak, and it did clear it up enough I can drive it and rev it. It still isn't 100% and bucks a little bit at full boost but its totally doable now and Ill be able to clear some problems up as I go. Thanks ya'll

 

[mk2 supra]

Id like to update this. I thought I had it figured out but the car threw me for a loop again lol. The post MAF leak helped it a lot, it was perfect up to 3k WOT then would start to studder a little (but still pulling, seemed lean) Well it just went downhill and got worse and worse and within 3 days of driving it was back to how it was in the video again! I checked for any boost leaks over and over.
On a hunch I got a deal on a GM MAFT, slapped it on and that did it. I have no clue why the car would still do the same symptom with the MAF unplugged and CEL triggered (meaning limp in mode) perhaps the ecu goes off its previous learned values, which were lean and crappy, but yeah, thing is a whole new animal! Finally running like it should. Thanks for the help guys, now back to breaking in the clutch/engine, a few more upgrades and Ill hit the track and hope for high 13s

 

[justin.daniels2]

I had somethin like this happening on my mx83 recently, so I changed spark plugs today (lookin like time for rebuild to be honest, oil soaked inside n out on plugs then I pulled cel codes, bad coolant Ecu sensor an somethin up with the knock sensor. So I changed the Ecu coolant sensor an it stopped being lame. Still need to change knock but I'll likely just wait to pull the engine.

 

[jetjock]

...On a hunch I got a deal on a GM MAFT, slapped it on and that did it...

Huh? With a stock ECU sans translator that isn't possible.