Gen4 Swapped ST185 Stutters/Trembles When accelerating

Hello everyone,

New ST185 Owner and needed some help diagnosing my problem. The car has been driving with no issues until a couple days ago. While accelerating in first and second gear, the car trembles and shakes quite violently until I add more gas and it returns to normal. When I drive the car while stepping on the gas, it drives normally. This only seems to happen in 1st and 2nd gear. It also comes and goes, usually when I begin driving it in the morning its fine, but after lets say 15 miles it starts again. I have changed the spark plugs, checked to see if the turbo was damaged, and they all seem fine. I have been told there can be a boost leak, but wondering if it can be anything else. I can elaborate if it I'm not to clear. Thanks in advance for the help!

Michael

A leak somewhere after the AFM is possible. If your boost control is stock, I don't think you get higher boost levels until you are in 3rd gear or higher. And you won't get higher boost levels until the engine warms up. So it sounds like when you are "allowed" to get higher boost, and you use it, you may be leaking air somewhere after the AFM. If the air leak is substantial, the AFM is telling the ECU what air flow the engine should get, but it may be getting less (if leaking pressure after the turbo) or more (if leaking between the AFM and the turbo).

The question is - if it worked find up to a couple days ago, and nothing was done at all to the car just before these symptoms developed, it would be unusual to develop such a significant leak so suddenly without having done something in the engine compartment.

I can start doing the soapy water method and see if I can find a air leak some where, cause another all trac owner tells me it might be it as well.

Where I'm from, there are a lot of rally like roads that I have taken the car to and been practicing, but since the car has been lowered and I have yet to raise it to a better height I did hit the undercarriage quite a bit. I might have knocked something loose.

Its been pushing a lot of boost for a while as well, more than recommended for the 4th gen engine. But even with that amount of boost and driving it over 3000 miles I've never had the problem. When the problem started I wasn't even driving it fast, I was going around 35mph, on 3k rpm.

Do you have the stock ECU? And the stock MAP sensor?

Map might be stock ECU, Might not be. When I bought it, it didn't say anything about it being changed or not.

In one of your previous responses, you said "its been pushing a lot of boost for awhile as well, more than recommended for the 4th gen engine". The Gen 4 3S-GTE engine, that engine & turbo was designed for 13 psi max. If you are running a stock ST185 ECU on that engine, that ECU goes into fuel cut when the boost pressure exceeds 9 psi. Of course, the Gen 4 had a different MAP (which I'm assuming you are using on our ST185 with the swapped Gen 4 3S-GTE). If you are using the original ST185 MAP & ECU, you will get into fuel cut, which will have the symptoms you describe.

With swapped engines like this, one has to know what else was swapped with it (like the MAP, the ECU, etc.).

So, are you running the stock ST185 MAP & ECU? Not the MAP & ECU that would have been used with the Gen 4 3S-GTE?

I'm pretty sure I'm running an after market ECU and MAP since I'm pushing about 21 PSI. Been doing that for a while with no problem. That boost was set by previous owner. The only cut off it has is when it hits 115 MPH, that's when the gas cuts off.

Do you know if your aftermarket ECU has no upper boost limit to cause fuel cut? It would be best to know for sure what you have - as the symptoms are those tied to fuel cut being hit.

Just take a look at what your ECU & MAP is, so you know with certainty the problem isn't with either of these.

You're going to need to find out which ECU you are running. The factory location is behind the radio. Pull the carpet up from the passenger side to get a view at it. You can probably stick a cell phone in there and snap a photo without having to undo all of the nuts and bolts to pull it out.
You also need to figure out what check engine light codes are present. This could be fuel or ignition. Determining what code(s) the ECU is registering will go a long way in identifying the issue and resolving it expediently.

By the way, 3SGTE gen 1 and 2 had AFM/MAF devices in the intake tract that measured air temperature and volume. It's a flapper door and had both sensors in one spot.

Gen 3+ switched to dedicated temperature and manifold absolute pressure (MAP) sensors. There is at minimum one air temp sensor and one MAP sensor and both are installed in the intake manifold plenum. For some reason, Toyota also installed a secondary air temp sensor in the intake tract (pre turbo) on some models, but it's not as important as the one in the manifold.
This is important to understand as MAP sensor cars are more tolerant to boost leaks. It will still cause a fuel richness issue, but the MAP sensor is able to compensate much better than a car equipped with an AFM since it knows how much air (pressure) is in the intake manifold.

I prefer to check for vacuum leaks via spraying all of the air connections down with carb cleaner. If the idle raises, you have a vac leak. You should also have low vacuum on your boost gauge with a vacuum leak (if your cams are factory. Aftermarket cams inherently lower the vacuum).
Checking for boost leaks means you need to have compressed air and will either need to buy a tester or make one with a trip to the hardware store. A cursory google search returns https://turboboostleaktesters.com/how-t ... leak-test/ but you can find details and instructions everywhere.

either way, start with the codes. Don't bother making any changes without at least getting the right information first.

best of luck.

93celicaconv":klkhsl38 said:

Do you know if your aftermarket ECU has no upper boost limit to cause fuel cut? It would be best to know for sure what you have - as the symptoms are those tied to fuel cut being hit.

Just take a look at what your ECU & MAP is, so you know with certainty the problem isn't with either of these.

Click to expand...

There is no fuel cut, since I've been running it the same since I bought it and I never had the problem before. I know forsure the only fuel cut is when the MPH hits 115. I'll try to take a look at the ECU and the MAP today and see if that is the problem. Thank you for your input ! I really appreciate it.

grip-addict":15xzvryq said:

I prefer to check for vacuum leaks via spraying all of the air connections down with carb cleaner. If the idle raises, you have a vac leak. You should also have low vacuum on your boost gauge with a vacuum leak (if your cams are factory. Aftermarket cams inherently lower the vacuum).
Checking for boost leaks means you need to have compressed air and will either need to buy a tester or make one with a trip to the hardware store. A cursory google search returns https://turboboostleaktesters.com/how-t ... leak-test/ but you can find details and instructions everywhere.

either way, start with the codes. Don't bother making any changes without at least getting the right information first.

best of luck.

Click to expand...

Currently it sits between -9.0 and -8.7 (estimated, give or take a couple .1 ) PSI when in idle. It boosts fine (it has a HKS Boost Control) when I see it, it goes up consistently with no jumps to PSI.

That sounds fine. Please check codes next.

Is that vacuum reading with the engine warm? That's pretty low. My 4th gen engine reads 18 to 20 at idle. I would start by checking the vacuum lines around the wastegate and boost controller and make sure they're hooked up correctly.

dbucks2k":2wezp0in said:

Is that vacuum reading with the engine warm? That's pretty low. My 4th gen engine reads 18 to 20 at idle. I would start by checking the vacuum lines around the wastegate and boost controller and make sure they're hooked up correctly.

Click to expand...

I think there is confusion on the "units" of vacuum. The OP states his values are in PSI. I'm thinking yours is in inches Hg.

-8.7 PSI = -17.7 inches Hg
-9.0 PSI = -18.3 inches Hg