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> Engine bucks with no boost, Help me diagnose the problem
post Jun 12, 2016 - 10:28 PM
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IllIllIll

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Hi all,

I finally got my 97 Celica convertible running with a 3SGTE from a ST215 Caldina.

Anyway it finally drives, but I have a problem. Long post but I tried to post all relevant details of my car & it's problems.

It drives in boost fine, but sometimes after driving a bit when everything is warmed up, I pull away form a stop or slow way down for whatever reason the engine starts bucking bad like it's firing on 3 cylinders or something. It seems to only do this when I slowly tip into the gas, & it goes away after the revs build & i get into boost. My tach isn't working yet, so I can't say for certain but it probably struggles until maybe 3 or 4 thousand rpm. If I gun it from a stop it goes without a hiccup most of the time. The engine runs fine even when flooring it in 5th gear going up a hill at 45, the boost comes on quickly. At first I thought I left the trans in the wrong gear when I pulled away from the stop sign, but that wasn't it. I've never had a slipping clutch, but I don't think that would cause the engine to buck, it would just go up in rpms without me going any faster if that was the case right?

I checked the spark plugs & they look fine, no odd smells or odd coloration. The oil isn't frothy & the coolant isn't oily. I have no visible smoke coming from the exhaust. I shorted the diagnostic pin & i don't have any codes. I checked my wiring again, nothing out of the ordinary.

I'm really stumped as to what is causing this issue. I am using all the stock Calidina sensors, ecu & turbo, so I would think it should all play together nicely & not give me any driveabilty issues like this if everything was working right. I have so much changed from stock with this swap, that I'm sure it's something I did or didn't do.

I am using the stock 5SFE 5 speed transmission, with a Fidanza aluminum flywheel, & a short throw shifter. I'm using the stock st215 injectors, fuel rail & fuel pressure regulator all fed by a new 355lpm warlboro fuel pump. I bought a new fuel filter, new belts & plugs & changed all the fluids. I did the wiring myself, but in hindsight I should have had Dr. tweak or someone do the harness for me as it was a PITA. I still haven't gotten the tach, A/C, or cruise control working yet. All of the wiring runs through the stock grommet so I extended the wires to reach the caldina ecu mounted in the stock location. I have the wires secured pretty well, but I wiggled everything around when the car was idling with out any problems. I even rechecked all the wiring for continuity since I got car running. I'm not using the fuel pump resistor as I couldn't figure out how to make it work, so the fuel pump is always running at full speed. Maybe that's the problem, idk. It's also an automatic ecu, but all the auto stuff is de-pinned & the wires removed from my harness.

I clocked the turbo outlet down, relocated the stock waste gate actuator, & extended the waste gate rod to set the car for 14 psi maximum boost. I'm using 2.5" aluminum ic pipes run to the FMIC & into the stock 3SGTE throttle body. I have the recirculating valve from the stock top mount setup dumping to atmosphere right now. I am using the stock turbo & the first half of the stock down pipe. I cut the stock catalytic convertor off right after the turbo & welded 3" exhaust tube on to what was left. From there I welded together a 3 inch exhaust with a high flow cat under the car near the transmission, a straight through resonator before the rear axle & then into a Dynomax Vt muffler with a single 3 inch inlet & pair of 2 or 2.5" inch outlets. This muffler has flap inside that opens up under high load to make it a straight through type muffler when your foot is in it. The flap is spring loaded at low exhaust flow to close and this really quiets the exhaust down. It's a convertible & I didn't want it crazy loud inside when driving. It's quiet as stock at idle & until I get my foot into it & give it some boost then it opens & sounds quiet nice, at least to my ears. I don't my exhaust is the problem, as I think I remember the engine bucking like that when I had the stock exhaust bolted up for the first test drive. It was last fall, so I don't remember, I welded the new exhaust together over the winter.

I might not have all the vacuum hoses routed like stock, as I'm not using one or two of the vacuum switching valves. I have an aluminum radiator & 2 of the biggest aftermarket electric fans I had room for. The engine sometimes gets up to 220 degrees F according to my real temp gauge, & the fans cool it back down to 180. I think I have a boost leak as I can hear a hiss when I'm in boost, but I haven't been able to locate it. So I know I have a few things to sort out, but none of that should cause the car to behave like this.

Please help.
post Jun 13, 2016 - 9:13 PM
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enderswift



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I had this. it's the o2 sensor


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post Jun 13, 2016 - 9:45 PM
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IllIllIll

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I considered that, but wouldn't it throw a code if it was the O2 sensor? I still have no codes even after driving it around today trying to figure this out.
post Jun 13, 2016 - 10:21 PM
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IllIllIll

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I think I may have figured out my problem tonight. I don't have BOV or re-circulation valve installed at all. I was thinking I left the stock one in place, but it connects to the Caldina top mount, which I didn't use so I couldn't. I forgot about it until I was looking at the engine again today.

I found this searching the web tonight & I think this is my problem. The last paragraph before the conclusion at the bottom of the page says
QUOTE
"Another very important reason for having a diverter valve is for the benefit of the engine management system. Compressor surge in modern cars can have the potential to cause drivability issues such as jerking or "bucking" during a partial throttle lift, most commonly affected cars are late-model Mitsubishi EVOs. Whilst the factory valve is designed to eliminate this issue, it also prevents higher boost pressures being used and doesn't offer the maximum possible throttle response, opening the door for a well designed aftermarket diverter valve"


I know I'm getting compressor surge from the sound, after watching the youtube video & that's what's giving me the drivability issue I think.

Any one care to agree or disagree?

I won't be able to test my theory until this weekend at the soonest.
post Jun 14, 2016 - 11:29 AM
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Smaay

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its very possible its surge, you really need a BOV in there. Do you have a wideband O2 sensor? what are the A/F when its bucking?


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2001 Celica GT-S Turbo
1997 Supra TT 6speed
1997 Celica 3MZ/1MZ swap
1990 Celica All-Trac
post Jun 14, 2016 - 5:56 PM
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enderswift



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mine never threw a code. if you had compressor surge it would be pretty obvious, at least it always was for me whenever the bov vac line came off

This post has been edited by enderswift: Jun 14, 2016 - 6:58 PM


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post Jun 17, 2016 - 7:20 PM
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IllIllIll

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QUOTE (enderswift @ Jun 14, 2016 - 5:56 PM) *
mine never threw a code. if you had compressor surge it would be pretty obvious, at least it always was for me whenever the bov vac line came off


It's definitely compressor surge that I'm hearing, I listened to a video on YouTube & it's what I'm hearing. I'm not 100% sure that it's the problem i'm having, but I want to run a BOV anyway. I need to add the BOV this Sunday hopefully.


QUOTE (Smaay @ Jun 14, 2016 - 11:29 AM) *
its very possible its surge, you really need a BOV in there. Do you have a wideband O2 sensor? what are the A/F when its bucking?


I lost my wide band bung when I was welding together the exhaust, I have another one coming from Amazon & pnce I get it the wideband will be going in. My wide band directions says 18 inches from the turbo outlet, so I guess it be mounted down low right at the end of the downpipe
post Jun 22, 2016 - 8:12 AM
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celica91gts

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its weird, because you think compressor surge would happen when the OP is off the gas since the compressed air is hitting the closed throttle body. The op is having surge when he's slowly rolling from a stop where there is little to no boost and the throttle body is slightly open. Right?

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