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This problem is brought up on this site about 3 times a month, so I hope that putting the diagnosis with an easy-to-find title may give some a head start. There is nothing “new” in this post.
While there are many things that can cause your rig to quit running, this particular situation is commonly a problem in the VAF-COR circuit. Fortunately, it’s the easiest thing on your whole vehicle to diagnose.
Using your Special Service Tool (paper clip), jumper FP to B+ in the diagnostic connector.
If your rig starts and runs now, you have a VAF-COR circuit problem. (I’m using an ammeter to short FP to B+; the pump draws about 4.3 amps.)
Some cars (at least some Hondas) will run the fuel pump for about 5 seconds when you turn the key to ON, probably to pressurize the fuel rail. Not your Toyota. The fuel pump does not run until you turn the key to STArt. That signal powers one of two coils in the Circuit Opening Relay (COR), which then powers the fuel pump It immediately pressurizes the fuel rail and the engine starts. Once the engine is running and sucking air, the vane in the Volume Air Flow meter (VAF) closes a switch and grounds the second coil in the COR. The second coil holds the relay closed after the STArt signal goes away.
Since yours starts and runs, at least for seconds, your Fuel pump, ½ of the COR, and the STArt switch are all working. Before you leave the diagnostic connector, check that it’s working. With key-on, you should get 12v to ground on B+.
With key-off, you should get low resistance (I got 3.4 ohms) to ground on FP.
If these tests fail, you have a wiring issue in the diagnostic connector (and you can’t trust your test of the VAF-COR circuit).
If you have a crank-no-start, you do these same two tests. No voltage on B+ means you’re not getting voltage through the EFI fuse through the EFI relay. High resistance to ground on FP means the fuel pump is blown, or you have a broken wire to the pump.
Hey! Since it runs with the jumper in, aren’t I all set? Do I really need to “diagnose” something that is no longer a problem for me? The whole point of this design is to assure that the fuel pump stops running if you get into an accident that breaks a fuel line. So, no, you can’t drive around with the jumper in. Too dangerous.
Before you jump into the nitty-gritty of diagnosis, check the obvious. Is your fuel gauge on E(nough)? Do you have all the induction plumbing connected? Back in the days of carburetors, you could remove the air cleaner and have no trouble running the engine. You can’t do that with a fuel-injected engine. Is the cable to the VAF part of your local rat’s diet?
For the VAF-COR circuit issue, start with the VAF. Remove the big pipe to the throttle body, so you can access the vane.
With key-on, open the vane with your finger. (Use your finger, not the screwdriver in the photo. I can’t get a picture with my fat hand in the way.) If it is working correctly, you should hear the fuel pump. But presumably yours is not working correctly. Remove the connector. Don’t remove the screws! With your multimeter, check for continuity between Fc and E1 on the VAF with the vane open.
If that passes, on the connector side check for 12v to ground at Fc with key-on.
(You’re measuring voltage through the second COR coil and through the wiring. In this picture, I’m measuring the current to ground to close the COR – about 80ma.) Check for continuity to ground on E1 on the connector side.
Note that my FSM does not match my truck; Fc and E1 are reversed. It doesn’t matter on the VAF side; that’s just a switch, so it has no polarity. But I’m suggesting you test for voltage on the harness side, and 12v is found on the second pin (so that’s Fc). Continuity to ground is on the first pin (E1).
If no continuity to ground through E1, you have a broken wire somewhere. If you have no voltage to ground on Fc, you either have a bad COR or a broken wire. (Remember: key-on.)
If the COR is good, you probably have a broken wire to the VAF. Check for continuity to ground at the FC pin of the COR socket with the VAF vane open. If no continuity, the wire to the VAF is broken.
As a sanity check, in the COR socket, jumper B+ to FP. With key-on, you should hear the fuel pump run. Here, the pump is drawing about 4.3 amps.
If you did all these tests, you have now checked every possibility.
The hardest part of the whole affair, and this is from personal experience, is, once you've identified that the COR is bad, if it is, is trying to talk the Toyota parts counter guy through just exactly where to find the COR. I had to physically go to the parts counter, and point to show the guy just where the COR could be found, on his little diagrams on the computer. He'd never looked up a single part for one of our trucks. They're older than he was by about 10 years.
He was amazed that the 4Runner was still going strong. My wife and I held off on laughing at the parts guy. At least until we got into my pickup with the new COR in hand, and were headed home. Then we laughed most of the 30 min trip back home.
I usually take a picture of whatever part I need to the toyota parts department in my home town.... they're awesome but have NO CLUE what your talking about in most cases. Lol
... I had to physically go to the parts counter, and point to show the guy just where the COR could be found, on his little diagrams on the computer. ...
Don't be so hard on him. You know your truck inside and out, but this is the very first one he's ever seen.
Instead, go to a dealer site (I like https://parts.lakelandtoyota.com/). Find the drawing with your part, and get what you think is the part number. Print the drawing, write down your try at the part number, and WRITE YOUR VIN ON THE DRAWING. (Many parts depend on things you wouldn't expect, like body style. The VIN is the key.) Use this drawing at the parts counter. It not only makes things go much easier, but it might convince the gal behind the counter that you "know what you're doing," and are less likely to waste her time. At my dealer, that translates into a lower price!
The dealer sites have almost the same software that your counter-gal is looking at. After you've worked your way through it trying to find the part you want, you'll have a lot more sympathy for how hard it is to find a part!
Photos are a good idea (you've got a cell phone; there isn't much point to not taking a picture). But a lot of parts can't be identified in even the best photo. For instance, the parking brake cable is a slightly different length depending (I think) on body style. A photo of your old cable wouldn't help, but your VIN would do the trick.
Honestly, I don't have a cell phone. Well, I do, but it sits in a drawer, unless my wife and I are going to going separate places. I go to the store alone, or she doesn't feel good, and I have to run into town for an appointment or something. Then my phone sits in the pouch on my belt. I almost never take it out. That's why I almost never post pictures of my truck, and the work I do on it.
Just me, though. I spent most of my life without a phone, and never ever go on "social media", so I don't miss having one with me in the least. So, no pictures. Maybe I should start.
Our parts counter guy, not gal, sadly, seems like they grabbed someone off the street, and said look here for parts to him. If the vehicle is older than 5 or 7 years, he gets lost pretty easy. He can be guided at least. He IS willing to listen. Really surprized him when my wife took over pointing out what and where for me, when the steam started rising out my ears.
She didn't want me to get hurt. I tend to have a short temper sometimes. PTSD thing. My mouth can get me in trouble, and we need to be able to get parts from this guy.
I will start trying to do things the way you suggest, though. It's probably the best way.
Have fun, all!
Pat☺
[QUOTE=scope103;52457947]This problem is brought up on this site about 3 times a month, so I hope that putting the diagnosis with an easy-to-find title may give some a head start. There is nothing “new” in this post.
While there are many things that can cause your rig to quit running, this particular situation is commonly a problem in the VAF-COR circuit. Fortunately, it’s the easiest thing on your whole vehicle to diagnose.
"WELL DONE" Scope103.
Your post should be included in the sticky section of the forum with the title "MANDATORY READING"
That is the best description of the common sense sequence of trouble shooting a no start symptom I have ever read.
The illustrations are spot on.
Once again "WELL DONE"
Art.
Have had my 92 22RE pickup for over 5.5 years now. Yesterday my son called me, and said that the truck cranked, and then immediately cut off. Engine was spinning and firing...just not getting fuel.
Started doing the tests, and was getting nothing from the test port. Light bulb came on, and checked the 15 amp EFI fuse. It was blown. I thought this was an easy fix because there is a 15 amp horn/hazard right at the EFI fuse, so I pulled that one, and stuck it into the EFI slot. Truck cranked first lick, and then died. Pulled fuse, and dang it was blew again. I knew then a wire or something was shorted. Had it towed to a friends shop a couple miles away.
My mechanic friend called me, and said that somebody that owned the truck before me had bypassed the COR by running one wire from the COR to the fuel pump. I saw that wire behind the seat of the truck, and then it ran out between the bed and cab, and then up under the truck. I had seen it before, but thought it was for a PA speaker mounted on the bed rail of the truck. Anyway, the whole wire was burnt. The wire was actually a long piece of cheap white drop cord that had been pulled apart to make one wire. There was a cloth rain jacket behind the seat that was burnt a little bit from being in contact with the wire. Luckily, the rain jacket was flame retardant, or my truck would have burned.
The mechanic said he put it back factory, and the truck would not crank. Pulled the COR, and it was corroded. Cleaned it up with come cleaner, and it fired right up. Going to replace it soon because once stuff like that corrodes it comes right back. But for now it's working like it should be from the factory!
Put a dab of silicone dielectric grease into the COR's plug. It'll prevent corrosion for a very long time. I put that stuff into every electric plug I take apart before I put them back together, and it's made a huge difference in the corrosion trouble my 4Runner has ever had.
It's also fantastic for preserving rubber, like o-rings, seals, and so forth. Makes them last like magic.
i am going to be diagnosing my own no-start in one of my '87s. engine cold, starts just fine. after warm-up, with some heat soak "off" time, it does not start - rather, it coughs, but won't actually run. i know the fuel pump works in the key "start" position, and when i push the CSC button, it won't start. however, if i use a paperclip, it will start immediately (and i can hear the pump running when the key is "on"). i don't know, because of the noise of the starter, whether the pump is running during the "key in start" position - which is one of the things i will be testing with the multi-meter.
it will also start immediately if i restart it after turning the engine off when hot or warm with no delay, but a 5 or 10 minute wait will result in the no-start unless i throw in the paperclip. once the engine starts, i can immediately remove the paperclip, and the engine runs just fine, no issues. it just doesn't start without the paperclip when warm/hot.
i'll be back with test results. i do have a set of known good COR and AFM components from my other '87 and from my parts '88, so i could also swap stuff, but i want to solve via diagnostics instead of parts cannon, even though in this case the cannon is "free". (for instance, the COR is the same in the '87s and the '88, even though they are different engines - 22re vs 3vze - because i've pulled the COR already from the '88 and verified it is the same as the '87).
Very nice write up of how this circuit works, and I had missed the fact that once the fuel pump has been started, the relay second coil keeps the pump on without further input from the MAF set of contacts. That makes no sense because how would that circuit shut the pump off in the event of a wreck and the engine stalling? I am thinking the fuel pump set of contacts may be burned or dirty. My problem is that while driving, the engine sometimes dies as if running out of gas and will not restart, but after some period of time it will start and sputter a bit and then run normally. I am using an external pump because I have a 82 chassis 4x4 with a 92 2wd body and 92 22re engine. I added a 30 amp relay and wiring to the circuit because my new Walbro pump requires minimum 20 amps while the original pump fuse is only 15 amps. One final factor that may help diagnosis is that the check engine light has be showing a code for lean condition (I thought this was because the second O2 sensor is not installed) but that CEL disappeared after the most recent failure event and restart. At the moment, the truck runs great even bouncing around all over doing donuts in a grassy field and no CEL is showing. I want to sell the truck but want to fix the problem first as a matter of honor. Final diagnostic clue: I notice than when buying gas, there seems to be a "whoosh" when removing the fuel cap. I am running the 82 fuel tank and that's why I can't use an in-tank pump. I have run the truck on trips of 100 miles with no failure and other times barely get a mile or so.All ideas most welcome.
I opened up my AFM (air flow meter, I don't know why some folks call it other names) and the set of points for the fuel pump is so tiny I'm not sure it will be possible to clean it very well. The larger side does show black burn marks around the point of contact so I tried to carefully spray electrical contact cleaner on it while holding a paper towel under it and also mopping up overspray but I don't think this had any effect. The moving point is so small it's not possible to tell if it's burnt or not. Why would it be wrong to bypass this switch just for testing? Thing is, the problem is so intermittent I'll have to wait for it to fail before I can test anything. If new parts could be trusted I would just buy a new one, but several people have bought these reman from Cardone and had to open them and clean the variable contact path to make them work. I am tempted to reengineer the whole thing by just using a oil pressure switch as the safety circuit with a starter bypass wire.
Thanks for posting/re-posting this Scope103 ....You are Legend....I have read your replies and used your methods for years...
...As far as my problem, I will re-do my tests using your great images...but, if they all pass again, I may re-post a reply with my actual problem...I don't want to step on anyone's thread....
OK, B+-Fp should run the fuel pump when the key is on. If it doesn't, you have a bad wire someplace.
IF the fuel pump runs with the AFM held open, and the key ON, the COR RUN half sounds good, but the START half doesn't.
Does the fuel pump run with the key held to START, without the engine running, without pressing the clutch? It should.
IF the truck runs with the AFM (Air Flow Meter) door held open, it should run with no human interference. The flow of air through the AFM should hold the door open enough to run the fuel pump. If it doesn't, the fuel pump switch contacts inside the AFM may be bent or something. It shouldn't take any more than the air flow through the AFM to hold the door open far enough to run the fuel pump, by energizing the COR run half. The flow of air at idle is enough. If not, the switch needs alignment.
If I were you, I'd replace the COR, and make sure the wires to the fuel pump are good. BTW: if the fuel pump isn't in the tank, where do you have it? I'm just curious.
If the AFM doesn't run the fuel pump with the engine just at idle, it may well need to be replaced.
01-31-2021, 12:52 PM
