ilikai

Hello here is my problem. Car was driving fine. Transmission and engine seemed very strong. One morning I went for a drive and all of a sudden the truck would not rev past 2000prm. When it would hit 2000 it would then drop down to around 1500 rpm and surge back up to 2000rpm, then again when it hit 2000 it would drop down to 15000 rpm, and it would keep doing this as long as my foot was on the gas pedal. I pulled over and it continued to do this in Park, Neutral, Drive, and L and 2. Turned off the car and turned it back on. Still happened. Drove it home like that because I wasn't far. A couple days later I opened the hood and manually opened the throttle to around 5000rpm. At that point it did not surge. Took it for a drive and it rode fine. Until yesterday again the same thing happened where I was not able to go past 2000 rpm. Please help me if you can, the truck is driving fine once again but I know its gonna happen again. Any ideas willl be taken under considereation. Thank YOu

1993 toyota 4runner 4x4 3.O

I checked for codes and there are NONE! I used a Hotwire to check and all I got were steady blinks. I changed fuel filter thinking it was clogged but it still does the same problem. Because there are no codes my best guess is the FUEL PRESSURE REGULATOR because I seen a video with what seemed to be the same problem for someone else and he said it was the Fuel pressure regulator. I cannot seem to figure out what the problem is. This weekend I will check air intake and the throttle body. Can anyone out there confirm or shed some light on the idea that it is my fuel pressure regulator?! @Metalhead1 @offroadnutz @Shady Cadence

Shady Cadence

If it's flat out cutting off at 2000 rpm, I doubt it's fuel supply related. On mine, when the engine cuts out I'm losing the injector pulse, meaning the ECU is no longer opening the injectors until the rpm drops to 1500, then they come back.

Verify your injector control with a noid light.

EDIT: I may have figured mine out. Behind the driver's knee panel, behind the speaker are four ground wires. Two are white with a black tracer, two are brown, each pair go to their own connector. I replaced the terminals on both of these, and my issue seems to have gone away. Now revs 4000+ rpm at will, cold or hot.

If you have ANY rust around your windshield, I'd go straight to these connections. Good luck.

RJR

My suspicion when I read things like this is that you are triggering the rev limiter. These engines are rev limited around 7000 rpm - the ECU senses rpm and cuts off the injectors if you go try to go higher. So why might that happen at 2000 rpm or so? The most likely reason is a bad ground causing a noisy signal from the distributor to the ECU. When that happens there is ringing on the pulse going back to the ECU, resulting in a signal with multiple edges. The ECU will interpret those multiple edges as a 3-4x faster signal. So, instead of 2000 rpm, for example, it thinks the engine is running at 3-4x that speed, >7000rpm, and shuts it down.

I've got no proof of this, but Shady Cadence's fix, above, lends credence to the theory. Putting a good oscilloscope on the rpm input to the ECU would be instructive, I think. Also, if you have any way to read the data port, the ECU will tell you what it thinks the rpm is. If that's way higher than reality, you're closing in on the problem.

ilikai

Ok I think I see the wires but the terminals look flawless and don't show signs of rust, is there anything else that it could be?? I can try and swap the terminals out this weekend. If it is the Ecu, how can I be sure, and how do I fix???

ilikai

Where do I get an oscilloscope and is there a write up that shows me what to do and how to use it?? Also how do I read the data port? What is the worst case senario here?

Shady Cadence

Yeah, mine didn't look bad either, but replacing them has made a difference. If it is the ecu, you replace it. But before you do, verify that it IS indeed cutting out your injector pulse. Get a noid light and plug an injector connector into it, the light will flash when the ecu cycles the injectors. Also get an inline spark tester between a spark plug and the wire. Now start up, rev to cutout and see which, if any are dropping out on you. Just spark, and you might have an ignition sub system issue, lose pulse or both and you might be in my boat.
There are multiple ground points for the engine management system. Looking over the schematics, i seem to see a pattern in ground wire coloring. Accessories like the hvac, radio and lighting use ground wires that are white with a black tracer line, engine management uses brown. There's the two wires by the driver, one on the inside of the driver's fender near the air meter, and two or three attached to the engine on the passengers side of the lower intake manifold, you can barely see them looking behind the upper plenum. Be sure ALL these are clean and tight. Also verify your body to engine ground is good, this is on the driver's side bolted just below the coil/igniter running to the driver's side cylinder head.

EDIT; after testing the vehicle for a few days, I can definitely say that fixing these ground wires has solved SEVERAL issues with it . First off it's no longer tripping the rev limiter (an explanation that makes complete sense by the way, thank you very much RJR!). Secondly I'm no longer 3/4 to wot on acceleration, she gets up and goes with 40% throttle. Third, starting in cold weather (ie, 0° and colder-I'm in Minnesota) was a real chore. Long crank time, lopey start, and pig rich when it did. Now fires after 1 second of cranking and runs smooth at high idle.

It's like a different truck. Seriously.

I'm considering doing some sort of post about the importance of good grounds. I'm willing to bet a LOT of issues on these vehicles can be traced back to them, especially the "weird" ones.

Shady Cadence

So, did you swap out that terminal? Remember the issue isnt where the terminal contacts the body, it's where the wires are crimped into the terminal.

ilikai

Thanks for the reply! NO i did not swap the terminals, i removed and cleaned them, but after reading your last post I will re-crimp them. Is your 4runner having the same problem still? or did re-crimping the terminal fix the problem? Oh yeah and where exactly are these terminals. The ones I am looking at are the ones under the drivers knee panel to the left. I removed the knee panel for better access and was able to see the 2 whites with black, and the 2browns. If those are the wires you are talking about then we are on the same page.

Also just an update at what I have done.

I conducted a fuel pressure test because I wanted to rule that out. I conducted the pressure test and everything checked out good according to the FSM on fuel pumps. I drove the truck until the problem started to happen, which was only like 5 minutes! The fuel pressure remained constant at 40psi even while it was surging. The test also checks for problems with the fuel pressure regulator but only through removal of the vacuum hose at idle. I am still wondering if my problem lies within the Fuel Pressure Regulator or one or more of the fuel injectors them selves. Could a fuel injector be clogged?? ( I'm thinking no because my truck idles perfect!)

Thanks for your help, Aloha from Hawaii

ilikai

I forgot to mention the noid light. Correct me if I am wrong but if I get a noid light wouldn't I have to take off the upper manifold to test the injectors? And would that test still work without me driving and the problem occuring?

ilikai

Could you please send me a diagram or maybe explain to me where all those ground wires are that help you fix your problem??? pictures would also be a huge help. Thanks in advance I really need my 4runner back hahaha

Shady Cadence

Yes, replacing that one connector with the brown wires eliminated the cut out, but also eliminated a hard start, long crank time, lack of power and inability of the ecu to recognize throttle switch state. And moved my fuel economy from about 10 to 16 mpg.

So yeah, I HIGHLY recommend it.

ilikai

WOW! I will do that as soon as I get time. did you just cut, strip, and re-crimp?

Shady Cadence

Yup, that's it. Way too simple, I know.

ilikai

Wow ok i don't know for sure if this worked yet but i just sanded down the terminal and the washer and all that metal from the brown terminal. I didn't have another terminal so i didn't replace it. I took the truck for a drive and the problem did NOT happen. I drove farther than I did this morning and the other day when i went for trial runs. I will probably go for another drive shortly to see if it acts up at all!!!!! Thanks so much for the advice. Are there any other grounds that I should do this to?

CorsaRunner

That would be great if fix was as simple as this. I've got a 94 4runner with a 3.0 that does the same thing in regards to stumbling and not revving over 2000 rpms. Been trying to hunt down the issues with no success. Hopefully this weekend I can get some time to give this a shot.

Keep us posted with your fix!

Shady Cadence

Said he took it for a nice long drive and it didnt flinch, so I'm calling him fixed.

That being said, wanna be #3 in on the cheapest fix ever? Try it, and keep us informed.

ilikai

I replaced the brown wired terminal, and it ran fine for almost 1 week. I thought it had fixed the problem, but this morning it happened again. I don't understand how it can run fine for a whole week then all of a sudden go into that rev limit mode. I am going to replace the other white wired terminal next to the brown one but there is barely any room to work with that wire so we shall see...have you found a fix to yours?

ilikai

sorry to say, but the problem wasn't with the brown wires terminal. which should i replace next?

Shady Cadence

The ones on the back passenger's side of the intake manifold. Stand by the passengers fender and look between the firewall and the intake plenum, you'll see a bunch of wires going to one bolt.

Those.

Fraser

No codes on yours? I have a student with a '92 4runner with intermittent code 52, knock sensor, that does something really similar when it's acting up. It's probably the old harness pigtail crapping out when it get's jostled around but he hasn't fixed it yet.