IronsmanMedic

1993 4Runner 3VZE 6.0

Truck has been running like a champ recently...no warning signs of today's impending events; while driving at full speed down the freeway (65mph), I was about 500 yards from my exit and the truck died out of nowhere.

When she died, I didn't lose anything (PS, breaks, radio, dials, etc.). No CEL, no battery light, no "Christmas tree", nada...all of the sudden I had no engine noise, and she just started coasting (while still in Drive). I coasted to the right side of the freeway, put her in Neutral and tried to start her. She turned over very strong, but no start. Immediately jumped on Yotatech while I waited for the tow truck.

She's been home for about three hours now and this is what I have...

1. Fuel Pump works...I jump FP to +B in the diagnostics box and get a strong stream of fuel. I can also push the VAF vane and it will activate the FP.

2. Timing Belt is still there and keeping time.

3. I have spark across the board.

4. Starter is good.

5. EFI fuse and relay are both good.

6. If I pull the VAF Meter plug off of the meter itself, she'll start right up and run for about two seconds before quickly dying.

7. If I jump FP to +B with the VAF Meter plug connected, no joy.

8. If I jump FP to +B with the VAF Meter plug DISconnected, she starts up immediately and then runs (although very rough).

Is this a Circuit Opening Relay (COR) issue or...? I'm truly at a loss.

Here's where things are (to me) odd, when I pulled the VAF to check with my multimeter, the VAF itself checks out across the board (based on the FSM). When I went to check the connection (engine side), I appear to be missing what should be the E2 connection. I have all seven prongs (or whatever they're officially called) on the VAF side, but only have six wires and six "prong receivers" on the connector/engine side. *See Pic.

According the the FSM, I should only have six, but the "blank" hole should be the third from the left, when looking at the connector, not third from the right. O.o

IronsmanMedic

Edit: Was finally able to upload a pic (had to go through FB and then upload via URL).

RJR

I'll offer a bit of a theory. Since the problem appears to be somehow associated with the VAFM, I would theorize that the VAFM is telling the ECU that there is no airflow into the engine (keep in mind that the part of the VAFM that enables the fuel pump is a separate circuit that the ECU doesn't know about.) Given this (mis)information, the ECU does not pulse the injectors, so you get no fuel flow to the cylinders and thus no start. When you unplug the VAFM, the ECU reverts to open loop mode and pulses the injectors, although not necessarily optimally, so the engine runs, roughly.

I'd check the VAFM wiring really carefully, back to the ECU. However, as I said, this is just a theory. I may be all wrong.

You could pull a spark plug and see if it is wet from fuel.

IronsmanMedic

I actually came to the same generalized theory, after five minutes of forum searching while waiting for the tow truck, RJR. I may not be a master mech, but I believe I know enough about engines to get most jobs done...so after a bit of searching, I was sitting there thinking to myself, "Ok, I have fuel in the tank and I can force it to the rails...I have spark...it turns over very strong...all fuses are good...and when I unplug the VAF, she starts for just a second, which is probably because the fuel pump isn't turning on (post-startup). But she won't start at all when the VAF is plugged in. I wonder if the computer thinks that there is zero air available/present, thus it's not pulsing the injectors at all."

This is why, after checking to make sure the timing belt was still in tact, I've been focusing my diagnostics on the VAFM. I've never had to deal with a COR before though. If none of the 3VZE jedi masters end up with some wise words for me, I guess I'll be searching for that little black box at first light (I need my truck tomorrow, no ifs ands or buts).

What boggles my mind is why all of the sudden...no warning signs, no symptoms, nothing has changed with my truck for weeks (except non-fuel, non-air, and non-wiring related things). Random failures piss me off, especially when they are failures in areas that shut the truck down completely. GRRRRRRRRRRRR!

RJR

I don't think it's the COR. Once you jumper B+ to FP, you've eliminated the COR from the equation - you've simply shorted around it. If the truck doesn't start then, the COR is not the problem. Besides, you verified the COR and fuel pump in step 1 of your original post.

The VAFM has two parts. One is a switch that closes when the vane moves even just a slight amount. That switch activates the COR and starts the fuel pump. The ECU knows nothing of this. The other part of the VAFM is a variable resistor which sends a voltage to the ECU proportional to air flow. That's the part that appears to be, for whatever reason, sending bad data to the ECU. I'd check for a broken wire between the VAFM and the ECU, in particular the one that comes from the "wiper arm" of the VAFM.

RAD4Runner

Like Ron et al mention above regarding VAFM temp/flow measurement.
Temp-sensitive resistor/wire not connected, with some fuel pressure left in line = starts but dies.

Fuel pressure present but temp-sensitive wire/resistor connected= No combustion.

8. If I jump FP to +B with the VAF Meter plug DISconnected, she starts up immediately and then runs (although very rough).[/QUOTE]
Fuel pressure present, AND temp-sensitive wire/resistor not connected = combustion but rough.

Like mentioned ^^^ ECU is getting wrong temp input.

Based on above, there's combustion (although rough or short-lived) when resistor is NOT connected. Therefore, it could also be a short OR too low a resistance in temp resistor/wire circuit. You might wanna check specs for lower limit on resistance, too.

IronsmanMedic

I think I'm following on the diagnosis...forget the page, we're not even in the same book when you start going into what I'm to check specs on (not to mention how to do it). LOL

scope103

I wouldn't pay TOO much attention to that. First, the FSM shows the connector looking into the VAF. Your photo is looking into the connector going to the ECM. So your "pin 3" is third from the RIGHT, while the FSM shows it third from the left.

To make matters more confusing, I have two FSMs for my truck, and they are different on the VAF wiring, in what appears to be an insignificant way (both E1 and E2 are just grounds, why would there be two?) So I think you're okay there.

RJR's analysis, as tentative as it is, seems right on to me (he seems to know a lot about the VAF, and more importantly, can explain it). So I'd stick an ohmmeter on pins E1 and VS, and slowly swing the vane. The absolute numbers aren't so important, what you want to see is a smooth, monotonic change in resistance. If it drops out in places (particularly at "NO" vane opening) that could cause your odd symptoms.

Last, kudos to your for your careful, systematic approach to the problem. We may be mostly guessing, but we're not totally in the dark!

RJR

Also check continuity of each wire, especially the VS wire, back to the ECU. The reason I suspect a broken wire is because of how suddenly and completely the engine quit. A flakey VAFM would have bad spots and good spots, I think, and give you more of an intermittent problem.

Here's a snippet of the wiring diagram. Pins FC and E1 of the VAFM control the COR. Pin VS tells the ECU how much air is flowing. VC is at +5 volts, and E2 is ground. Pin THA sends an air temperature signal to the ECU.

IronsmanMedic

So my plan was to go through and check the wiring from the connector to the ECU this morning. Late last night, I decided to go back out and pull the VAFM again and bring it inside for another round of testing (just to confirm that everything was good with the meter itself).

Putting the meter through the FSM paces, I was getting erratic readings (sometimes the numbers were good, sometimes they weren't). Thus, I said to myself "Self, if the meter is bad, you're possibly going to have to replace it anyway. Since you don't necessarily have the capital to drop into a new one and even a used one would be a stretch, AND since you need your truck tomorrow, you may as well open her up and see if there's anything you can do to get this thing working according to factory specs."

So that's what I did...I cut out the silicone and popped that top right off. I figured, even if all contacts were good and everything was as it should be, it would still be a benefit to test everything, bypassing the "pins" of the connector..test the temp sensor and such directly from the board/wires. That way, if each individual component checked out from the inside, I'd be able to temporarily hardwire the VAFM to the wiring harness to get me back on the road this morning.

Well, to my surprise, none of the pin-to-board contacts were actually connected to the board. Sure, they were sitting in roughly the proper position, but they weren't actually soldered down to the board. The traces were all there, but one of the copper pads had come completely off (E2).

Long story short, I ended up risking it all and attempting to solder everything back up.

After a very tense 30 or so minutes, the soldering was as good as it was going to get, considering how large of solder I was using (and was using a soldering iron that was way to powerful for such small detail work).

Ran through the FSM steps again...SUCCESS. Solid (ish) numbers across the board. More importantly, consistent numbers. Ran through the steps half a dozen times and was reading identical each time. THANK GOD!

At first light, I put the ol' girl back together, said a quick prayer, and she started right up. Put her through her paces on the street and highway...she's purring like she should (maybe even a bit better than before).

Maybe this is why she's been running a bit rich lately...erratic signals (data) being sent to the ECU causing more fuel than necessary. May lean out the meter by a click or two before apoxying the cover back on...mabye.

For all those who doubt these things are fixable, my experience shows that if you break the contacts (assuming traces are still good, and you have a soldering iron and some solder, AND you have a steady hand and some patience, you should be able make it work. I had to dig online to find good photos of a pristine VAFM as reference, so here are some photos I took before and after...just in case it can help any of you in the future.

Many thanks to everyone who spoke up and helped me sort out the symptoms and such yesterday. I appreciate your time greatly!

dromomaniac

Well done! You're a great example of why Yotatech rocks

IronsmanMedic

I'm having upload issues. I'll log back in later this evening and attempt to upload the remainder of the images I have.

Yotatech FTMFW!

dromomaniac

Farking Acronyms. That's an improvement on FTW, however (after looking it up)

I've been soldering like a madman at work the last two days--something I don't usually do--and was stoked to read about your fix

IronsmanMedic

This is only my second time soldering; the first time being when I hardwired my new injector connectors into the existing wiring harness (about a month ago). I watched a whole bunch of "circuit board repair" videos on YouTube before attempting surgery on the VAFM last night. The meter was broken anyway, so I figured "what's the worst that could happen, I screw it up and it's still broken." It was worth a shot...

Between the injector connector soldering and the circuit board fix last night, I think I've got the hang of soldering basics.

RJR

That's great work, Ironsman! Glad it fixed your problem. No reason not to try when it's broke already.

The chances are someone tried to take the AFM apart by unscrewing the connector body and trying to pull it out, instead of cutting off the RTV sealant and popping the top. If you try to pull the connector body out, it will tear the traces off the PC board.

IronsmanMedic

That's what I'm thinking too, Ron. I figure the Southern CA freeways (which aren't the smoothest of roadways) must have finally taken its toll on the already compromised contacts. I was slowing quickly when she shut down the other day, so the contacts must have finally had enough and shifted just enough, thus not playing nice with the ECU.

I'm going to carry my soldering gear with me in the truck for the next few days, just in case it needs a touch up, but so far, alls well that ends well. :-)

Thanks again for your help!

RAD4Runner

Suweet!


Yes, same thought here, Ron. Pulled copper pad right off.

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