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Discussion Starter · #1 ·
Let me start with the fact that I am not a transmission expert. I barely know the basics of how an automatic trans functions.

This was an intermittent problem with the van when I first bought it, but it has now transcended to a full time issue.

The van drives normally when I putter around town and on the highway - but when I floor it (regardless of the how fast I am going), the van will downshift and rev up, but I won't really gain any speed.

I've added about 1/2 a quart of Lucas transmission stop leak after reading about similar issues with the 4L60E, but I haven't noticed any improvement.

Could this be a sign of my TCC solenoid going bad? How should I even begin to diagnose? I have a scan tool, but I'm not sure that it reads any transmission codes. I have no check engine light, no codes present, and all monitors set.

Thanks
Max
 

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Common Sense + Critical Thinking
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Is this the 99 Drug Mule edition?

Always helps to put the year/model/drive/conversion etc in your profile or signature so we know what we are working with.

Did you ever do your LIM? Injectors? Any codes or check engine light? Misfires? Change your fuel filter with the new pump? Test fuel pressure?
 

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Discussion Starter · #3 ·
This is the mule, lol.

It is a 99 2wd with 157k miles on it.

I have not done the intake manifold gaskets, watching my oil and coolant and levels on both of those have stayed steady.

After the lift and big tires, I haven't done anything but drive it. I have no misfires, the fuel pump and filter I replaced when I replaced the tank (new tank was nice and clean before I put it in). No codes, no CEL, I haven't checked the fuel pressure because I assume it's good considering the pump is only a few months old.

Max
 

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Discussion Starter · #4 ·
Also worth mentioning, the fluid is nice and red and does not smell burnt.
 

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I had a similar problem, try cleaning your MAP sensor all you need is a screwdriver and a can of MAP Cleaner. For less than $15 you might get lucky, either way no harm done.
 

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Discussion Starter · #7 ·
You mean MAF? Mass air flow sensor?

I will do that. Definitely worth a shot, this vehicle was not super well maintained for the last few years.
 

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Discussion Starter · #8 ·
So, the issue has progressed. Still no check engine light, of course.

I was driving today and I was able to achieve progressively lower speed. Down to about 35 mph now. I did clean the MAF, and it improved the idle but the van still cuts out when I am accelerating. However, the van also cuts out when idling for extended periods now too.

Per the live data on my scan tool, short term fuel trim on S2B1 (downstream) oxygen sensor shoots up to 50% when the engine starts bucking and missing, which leads me to believe I am losing spark/ignition when this is happening. The van will die on its own if I let it buck and sputter, but if I let it sit for a few minutes it will fire back up and run great.

In desperation, I purchased a new coil. That did not fix it. I will try a new ICM tomorrow, will hit the junk yard and grab a few from any 4.3Ls that I can find. I will also pull an O2 sensor out to check for a clogged cat, though I feel that is an unlikely issue for these symptoms.

Since I am fairly sure this is not a transmission problem, mods please feel free to move this thread to the engine subforum.

Please anyone feel free to chime in with advices or suggestions.
 

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Pull up O2 voltage for the front sensors on your scan tool and do a full throttle run. If you can, record it so you can post it.
 

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Discussion Starter · #10 ·
On B1S3 I got it switching normally between 0.65 - 0.85 under normal driving, when I gassed it it dropped to 0.055V. I did not do the other upstream sensor.

I'll try to upload the video of the upstream sensor.
 

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Really should be looking at the front sensors, but looks like a fuel delivery issue.

Time to borrow a pressure gauge and have a look at your fuel pressure/leakdown.
 

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Discussion Starter · #13 ·
I thought so too, but when it starts acting up my downstream O2 fuel trim shoots up to 50%, indicating it is getting plenty of fuel but not sparking.

I will rent/borrow a fuel pressure gauge and see what I'm getting.
 

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Discussion Starter · #16 ·
Check MAF connections, holes in intake hose, cap over throttle body. Sounds like an intake issue.
I have not checked the cap over the throttle body. Do they have a tendency to crack?

For the record, all the other items you mentioned are in good shape, and I am not getting any codes for the engine running lean.
 

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I thought so too, but when it starts acting up my downstream O2 fuel trim shoots up to 50%, indicating it is getting plenty of fuel but not sparking.
Ok, so fuel trims are the computer's reaction to what it is seeing from the sensors. An example would be if it detects that it's running leaner than it should it will ADD fuel, if it detects that it's too rich then it will subtract fuel.
Positive numbers = the computer is adding fuel, negative number is the computer removing fuel.

The O2 voltage is the actual reading from the sensor, and regardless of anything else it should be rich during WOT. Which is exactly where your O2 voltage seems to be falling flat on it's face.

Fuel delivery does not = only the fuel pump. It's the entire system of a tank(to hold the fuel), pump(to create flow), filters(to keep crap from plugging the injectors), regulators(to create/maintain a restriction to build proper pressure), injectors(meter fuel to the engine), supply/return lines(to move the fuel around), etc, all working together.
 

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Discussion Starter · #18 · (Edited)
Good to learn new things - I still have quite limited knowledge on OBD2 diagnosing.

The pump, tank, and filter are still relatively new. If I find that I am losing fuel pressure at higher RPMs, is it safe to assume that I have a bad fuel pressure regulator?

If I have to do the regulator, I may as well spring for the MFI spider upgrade and just do it all at once. I will rent the fuel pressure gauge as soon as I am able.
 

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I agree, always great to learn new things!

Well, there are a few tests that you can do to determine why/where/how. I guess a dirty MAF sensor could cause a similar issue. If you check/clean it make sure to be gentle and only use MAF cleaner.

Here is an example on my 03, doing a WOT run tonight on the way to the store.
App is AndrOBD, available on F-Droid AndrOBD | F-Droid - Free and Open Source Android App Repository

You can see the O2 voltage fluctuating back and forth showing lean/rich like it is supposed to while I'm just sitting there. Then when I hit WOT you will see that the voltage shows it going rich and staying there for the entire WOT run.

Light Black Infrastructure Fixture Lighting
 

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Discussion Starter · #20 ·
Will,

Do you know what fuel pressure readings I should be getting while the van is running? I picked up a pressure gauge and got some readings. The pump in the car is a masterpro brand, which is O'Reilly's brand name I believe. Hard to stomach that I may have to spend another few hundred dollars on an OEM pump, plus drop the half full tank.

Starting and running, the pressure stays around 50 psi. If I punch the throttle, it drops down to ~30 psi. Seems you were right and my problem lies in fuel delivery.

After getting confirmation from you that the diagnosis is accurate, I get to see if O'Reilly's is going to fight me with the pump warranty.

I know the video isn't the best quality, but I tried to narrate it as well as I could.

 
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