Hi, first post, desperate enough to make an account. I've done my best to read up as much as I can on this issue but either I'm doing something wrong or the fixes aren't working for me.

So, I bought my '86 4Runner a few days ago. When I showed up the guy said he couldn't get it to start because he'd just washed the engine compartment. It did start eventually, ran pretty rough, died on me while pulling out to drive it. After another few mins in the sun, it fired right up, ran great. Never missed a beat, took it on a long test drive, all was well. Bought it, took it home, ran it a few times showing it to folks, parked it for the night, and in the morning started on the exhaust manifold (had a really bad leak, turns out it has at least 4 bad studs/threads, so the new one is gonna leak too). The exhaust manifold is the only thing on the truck I touched (well that and O2 sensor, put in a new Denso), and as soon as I was done, I went to start it and it died right away, which is where it remains. Absolutely no change, if it sits for a few minutes it'll fire right up then die in one second. Then if I keep cranking after that, nothin'. So, I got to work trying to figure out what's causing it.

First I researched how to check the fuel pump, and settled on two methods: jump a test connector, and manually actuate the AFM by adjusting the gear so the pump runs as soon as the key is turned to "ON" (and then returned the gear to its original spot). Both methods turned on the fuel pump, I could hear it going, but no change in the start. So I hooked up a fuel pressure tester to the cold start injector, and saw 38PSI when cranking, which as far as I know is in spec. So I'm somewhat convinced it's not the fuel pump, but figured I'd have a look at the strainer. Went to take the fuel pump out, and cannot for the life of me get the high pressure hose off of the hard line from the sender. If I try any more I'm going to twist the hard line in half. So, I'm leaving that alone for now unless it seems like a pump change is a good idea. Even then, I don't know how I'm going to get the sender/hanger off of the hose without breaking it, and it doesn't look like they're very available.

Next I went after fuses, pulling and checking them all individually. They all look fine, but there is some evidence of damage on the driver's side fuse block. None of the fuses are blown but the plastic is kinda blackened in spots. Under the hood, the 80A fusible link looked kinda greenish and corroded, so I replaced that and the 30A and 40A fuses as well. The others look intact. No change.

I found some threads talking about the ignition switch, and it made sense that a bad switch could cause this. Replaced it, no change (except I left the key reminder buzzer unhooked, so that's a win).

I've tried a new cap, rotor, plugs, wires, coil, all with no change (stuff I was gonna replace anyway).

I thought maybe the fuel gauge wasn't working and I ran it out of gas, so I put 3 gallons of fresh fuel in, no change. Now I'm removing the fuel filter and replacing that, hoping for the best. I'll be headed to a wedding this weekend though and before I give up and tow this thing to a shop, I figured I'd make a post and ask for some opinions. I do a lot of work on my own vehicles but testing electrical circuits with a multimeter is pretty new to me and while I've seen some info about checking certain components this way, I'm not sure which ones should be my priority. The previous owner(s) have messed with a lot on the truck. It's got a starter mod done to it, different headlight wiring (H4 bulbs, not sure if they needed wired differently or if the harness went bad?), the original ignition switch was cut up in spots, the truck is wired very poorly for audio, the rear window switch is just coming out of the bottom of a center console that doesn't belong in the truck... lots of stuff going on but under the hood it looks like most parts/sensors/etc are original Denso. If anyone can offer a little help or advice I would appreciate it, I'm not sure how I've managed to screw something up by replacing the exhaust manifold, or if it's just bad luck. I'll be able to work on the truck a little bit today and then I'll be back at it next week, hopefully in the meantime we can come up with some ideas.

 

The MAF is right near the air filter box. Between that and the engine there is some sort of water catch with a hose coming off the bottom of the air duct to the engine. If it is loose or removed it will do exactly what you describe. The computer expects a different amount of air and somehow can detect a difference and then cuts off fuel from what I can tell. Make sure all air inlet tube connections are tight.
If that doesn't do it, I would suspect fuel relay but it has been a few years since I had to deal with that issue.

 

It sounds like it could be the COR. The Circuit Opening Relay. It's a safety feature that shuts off the fuel pump as soon as the engine stops. In an accident, you don't want the fuel pump running, pumping fuel out a broken line all over the ground. Definite fire hazard to the max.
A quick way to check things out is to put a jumper in the test connector, from Fp to B+. You should be able to hear the fuel pump running with the key turned to the ON position. If so, it's either the COR, or the switch in the MAF that closes as soon as the vane opens, even a very little bit.
Very easy to check. Pull the plug off the MAF, put an ohm meter between the two pins that the switch is on. Vane closed, switch open (infinity ohms). Vane open, even a small distance, switch closes (0 ohms). IF the MAF checks out OK, it's the COR.
If the fuel pump runs, you can try to start it with the jumper in. It should start right up. Do NOT drive it with the jumper in. WAY too dangerous.
If neither the COR or MAF, the fuel pump, or the wiring to it, are bad.

As mentioned, any air going into the throttle body is a bad thing. The big tube between the MAF and TPS, especially at the flexible corner pieces, can develop cracks. No good at all.
Also, ensure ALL the vacuum lines are in good shape, and going to the right places.

Make sure the timing is set, if you get it to start.
Good luck!
Pat☺

 

Spray starter fluid in when it wont start. If it starts after that you have a fuel problem, if it doesnt start you have an ignition problem.

shem

 

You may have unplugged the igniter when you replaced the manifold. I just did the same thing and had the same issue.

 

The two green plugs are the only things that could be unplugged right?

 

I've seen in other posts that people say it will run if they spray starter fluid into the throttle body - do they mean into the airbox before the VAFM? Or will these motors run even without the AFM?

 

It won't run without the VAFM and all the induction plumbing connected. To spray starting fluid (use sparingly!), you can use the vent that connects to the valve cover.

 

No change with starting fluid in the vent hose. Starts up and shuts off. Coil/igniter aren't unplugged, plumbing from air filter looks fine, cleaned throttle body/IAC, tested resistance on AFM all looks normal, jumped fuel pump connector, no change, COR is clicking when I try to start it. Drained gas tank, put 5 gallons of Premium in, changed fuel filter, no change. Running out of ideas here.

 

Just because you hear clicking, well, your truck doesn't care. So a good end-end test is to replace the fuel return line with a piece of suitable hose (6mm or 1/4") to a suitable container. Start the pump with the jumper. There's no spec, but I get about 1/2 liter/min. If you get significantly less, you could have a weak pump, a clogged fuel filter, etc.

Make sure the plugs are firing. There's nothing wrong with the old' hold-the-body-of-the-plug against the block test, but it's much easier to use your timing light's inductive pickup (don't have one? They're about $30, and if you going go work on cars you need one anyway). Test each plug wire; if the light flashes, you've got spark.

If you have spark on all cylinders, try to check ignition timing. It's tricky to do if the rig won't start, but if you can't see the mark at all, then something is wrong.

 

Does it need to be the return line? I drained the tank before I installed the new fuel filter out of the inlet hose, and I left the fuel filter loose because the banjo fitting wasn't sealing on one side. So it would be easy to take off the single line from the pump again and measure that way. I wanna say the fuel flow seemed more than adequate and 1/2 liter/min sounds about right. Didn't take terribly long to fill a 5 gallon can.

 

Relays stick. Did you try whacking the COR?

 

[QUOTE=Danson;52464645... I left the fuel filter loose ...[/QUOTE]If your fuel filter is loose (leaking), how would you be able to develop 40psi in the rail?

Checking flow in the return line is a (partial) test of pump pressure, pump flow, and whether the FPR works. If there is no flow in the return line, either the pump is not producing sufficient pressure, or the FPR is stuck (either will cause no-start). A fuel pressure gauge is a better test, but you need a gauge and the adapter to plumb it in.

The main reason you use the return line is that it is easy. Every time you open a connection on the pressure side, you must replace the crush washers.

 

Oh I just meant loose as in not bolted to the block. I have it temporarily bolted to the inner fender in case it leaks again but it looks good. The fittings are nice and tight now, I went through probably four sets of crush washers trying to get them to seal. I'll try that return line and see if the pump is going bad but it really looked like significant enough flow when I was draining the tank and it was bringing fuel pressure up to spec.

The other problem with it possibly being the pump is that the hard pressure line coming off the fuel hanger is quite rusty and seized, and the line is already twisted from the PO messing with it, so taking the hanger out is gonna mean cutting, flaring and coupling the hard line which is gonna be a pain. Buying a new one for $200+ is probably out of the question for now. I'm also worried it could be the injectors, just because I'm getting 38PSI at the rail doesn't mean it's going into the cylinders.

I do have a loose wire remaining under the intake, looks maybe white with a black stripe? It's too short to work with without removing the whole intake which I'm trying to avoid until I have to.

 

If you have measured the fuel pressure, testing flow in the return line isn't necessary (or, really, useful). (You did mention the pressure gauge; I overlooked that.)

You mentioned you had fuel pressure while cranking, but didn't mention the fuel pressure with the jumper. "Starts and then quits" is the classic sign of a VAF-COR problem. https://www.yotatech.com/forums/f116...-quits-312747/ The fuel pump runs with the key to start, but is not held running by the VAF-COR once you release the key.

The easiest way to check that is put in the jumper (check that you can hear the fuel pump running), then try it. Since you've probably flooded it at some point, you may have to play with it, but not much. If you've done all that, then I'm out of ideas.

 

I assume the FPR is inline before the cold start injector? That's where I've measured the fuel pressure but I have a hard time trusting the PSI of one extra injector when I have unknown pressure and function of four others. I thought maybe it would still be worth checking if the cold start injector somehow got gas before the FPR.

Maybe you can help me make sense of the jumper. I have jumped the fuel pump connector on the fender with a paperclip previously with no change at all, but right now with no jumper in the fuel pump is running with key on. I've messed with the AFM but even after setting it back to stock it seems the fuel pump is running even without the jumper in the ON position (not start). Is it foolhardy to just throw a COR and AFM at this thing? I tested the resistance of AFM and it seems fine but the seal was broken on the cover so who knows how it's been messed with. I'm just so confused because most things that would make sense have kinda been ruled out by the fact that it ran like a top a day prior, and the fact that it fires up for a second. Obviously I have the big three (air, fuel, spark) for at least a second.

 

Accidental double post.

 

The FPR is at "the end of the line." It works by sending fuel back to the fuel tank when the rail pressure gets above the set point. Measuring at the CSI is fine. It doesn't tell you whether you've got a bunch of boogers blocking your injectors, but given that you have "no-run" rather than "run like crap," I don't think that's your issue. (Just for completeness, note that the FPR "set point" goes up and down with engine vacuum. It keeps the fuel rail pressure a fix amount of pressure above the intake manifold, so the pressure across the injectors is constant.)

Well, that's not good. Here's why: if you get into an accident that breaks a fuel line, you want the fuel pump to stop IMMEDIATELY. The fuel pump should stop running when the engine isn't sucking air. You may have some aftermarket "modifications." I gave you a link to one of my posts that went through the electrics of the fuel system. I think you'll get some traction with your multimeter checking out what's going on with your fuel pump.

Yes. The "parts cannon" is always foolhardy.

You've got a fuel pressure gauge, so you're miles ahead of most of us. Put the gauge on, and try to start it. Does the fuel pressure drop, then the engine quits? (a wobble at the end is normal, as the intake vacuum slips away) That would be a fuel issue. Vice-versa, not so likely. Put your timing light on the #1 plug. Same analysis; if the light stops flashing before it quits, you have an ignition issue. If it keeps flashing right up to dead-stop, the problem is probably elsewhere. You've done a pretty good job with your 5 senses; don't shy away from some primitive (1990s style) tools.

 

Oh I know it isn't good! It's worse than me bolting the fuel filter to the fender even. I'm a bit confused as to why it's happening. I can manually activate the fuel pump by moving the arm inside the AFM of course but I'm not sure why it's turning on even without the jumper. It wasn't to begin with.

As for the pressure gauge, yes, the fuel pressure drops but it's hard to say if it's before it quits or right when it quits due to how fast it shuts down. I definitely have 38+ when cranking and then it falls to low 20s. I'll mess with it a bit more and report back, I appreciate the insight even if you're out of ideas. I can replace most anything on a car but I suck at diagnosing issues that aren't spelled out for me with an OBD reader.

 

It sounds like, to me, you fixed one problem. The fuel pump SHOULD come on when the vane in the AFM is open, even a little bit.

The fuel pressure dropping, if it does so before the engine quits, could be a lot of things. To me, since the pressure is good when cranking, the fuel pump, it's wiring, the AFM, and the COR are all good, with one exception.The COR has two halves to it. One half is engaged when you crank the engine, the other half takes over when the engine is actually running.
I can't recall if you changed the COR yet, but if not, it's something you should check out. It could also be the wiring associated.

The fuel pressure drop could be the pump stopping, for whatever reason, and the residual pressure left in the system is from the check valve on the pump that holds fuel in the system when the engine stops.

Alternatively, it could be some gunk in the FPR, it's diaphragm, or the vacuum line that feeds it. It could also be gunk in the pulsation damper, at the entrance to the fuel rail. Or it's diaphragm.

Nothing wrong with the filter being mounted on the side of the compartment. Many do that to make sure it is easier to get to. Only thing to make sure of is that the direction of flow is correct. It SEEMS backwards when installed normally. Just make certain the arrow points in such a way that the hose it points to is the one going to the engine, not the tank. It's confusing, because when it's mounted to the engine, the lines APPEAR to be the wrong way round, but they made the system so the fuel comes from the tank at the forward end, and goes to the engine from the rearward end.

Good luck!
Pat☺