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I am working on a 1991 Toyota 4 Runner with a 3.0 V6.
When I got it it had been sitting a while and cylinders 4 and 6 were not getting fuel. They were firing, but not getting fuel. I changed the plugs, wires, and new injectors. Put it back together and same thing. The plugs are firing at the cylinders, but the injectors are not letting any fuel pass through. This is only on Cylinders 4 and 6. I traced the black and red wires from the injector plugs back to where they all splice together. Cylinders 2, 4, and 6 are on one splice and the cylinders 1, 3, and 5 are on another. All connections look great, and there are no breaks in the wires from the connection where 2, 4, and 6 splice together towards cylinders 4 and 6. All the wires are fine. I haven’t traced the white wires back, I am looking for a wiring diagram for that, but what could be causing only cylinders 4 and 6 to not let fuel pass through?
I am doing a noid light test today to see if they are even getting the signal to pulse.
Good work so far. The Black-red wires are constant 12v with key-on. The injectors open when the the white (2-4-6) or white-red (1-3-5) are grounded by the ECU. (Yes, all 6 injectors open at the same time.)
Note that the fuel rail is pressurized from both ends, so even though the "short" route is from 6 to 4 to 2, you could have a clog so that injector 2 is fed from the "front," and 4/6 are getting no pressure. Or, there is a small filter in the top of each injector. You say the injectors were replaced, so I'm assuming you have NEW injectors and filters, but the rail could have had "gunk" and you just pushed that gunk back into the new injectors.
I'd back up and confirm your no-fuel diagnosis. You probably have the plenum off already, so try this setup:
[This was to look for a leaking injector, but you can use it to check for opening.] Pressurize the rail via the FP connector, and momentarily ground the white wire by back probing. That should open all three injectors, and the ends of the paper slips will show that.
As you can see in my photo, a VERY likely cause of your problem is a bad connection at the injector; don't miss that.
I going to try the noid light this afternoon to verify whether or not I am getting a pulse to the injectors. I have put it all back together right now, so I would have to take the top intake back off again (no big deal) but first want to see if I am getting the signal to pulse to those injectors. Is there anyway the ECM could be causing this problem? I don't see how since the injectors are all on the same wire and only two of them aren't working? Seems that once the pulse signal is sent through that wire, all of them should receive it rather than just 4 of them???
It very well may be gunk in the line, the truck was sitting up a while when I got it. and like I said my original problem was cylinders 4 and 6 not getting fuel, and I still have that problem. I think I will do the noid light, then depending on the outcome (if they all show a pulse signal), take the top intake back off and clean the fuel rail lines and hope it was just some gunk and do the paper test like you showed. But question...how are you saying to pressurize the rail with the FP Connector??
There are two injector wires (2-4-6 and 1-3-5), and as far as I know they are both grounded at the same time. But that doesn't matter to you anyway, IF 2 is getting fuel and 4,6 are not. Those three are all wired together.
In the diagnostics connector, there are the FP and B+ pins. When jumpered, the fuel pump is forced to run with key-on.
In addition to the noid light, in theory you can hear the injectors clicking when running. You'll need a stethoscope of some sort (a wooden dowel might work), and you'll need the engine to be running (which I'm guessing you can't do).
Yeah, the truck will crank and run, albeit not very good with two cylinders missing. Where can I find a diagram showing the FP and B+ pins and such. I don't have a service manual or anything for this vehicle yet, I just got it for a good deal. I am going to do the noid light, and listen for the injectors clicking any maybe have to take it back apart and check the fuel line for blockage and do your paper test!
The pins are labeled under the cover of DLC1, right next to JB1 (fuse box) under the hood. You'll need that connector a lot; you need to connect TE1 to E1 to get codes, to set the timing, etc.
Ok, the noid lights say the injectors are getting the pulse, I did the paper trick and jumpered the FP and B+ pins to activate the fuel pump, that didn't open the injectors though, but after I rolled the engine over a few times I noticed I was getting fuel through all the injectors onto the paper. So I put it all back together and cranked it up and it is still doing the same thing. It makes no difference in the engine idle when I remove the 4 and 6 plug wires form the cap. I took the plugs themselves out and had them plugged in and they are firing fine, so it isn't a spark issue. I found out it isn't a fuel issue., unless it just doesn't have enough fuel pressure when it's running to fully pressurize those cylinders???I'm thinking not likely. I notice these engine has the nickname of the 3BLOW, so I'm wondering if it could be a headgasket between 4 and 6 and dumping coolant into the cylinders and negating the fuel and not allow any combustion. It is smoking a little, but not like I would think if it were blown that bad. How can I check to make sure I do or do not have a blown headgasket? I was thinking unplugging the spark plug wire on those cylinders and letting it run a while where it isn't firing and then yank the plugs out quick and see if they have fuel/water on them????
Oh, I even plugged the noid light into the injectors on 4 and 6 while the engine was running to ensure it was still getting the signal, and sure enough it was..
The "paper" test is end-to-end, so it's not a fuel/injector issue. (Why did you think it was?) You could close the loop by putting your timing light inductive pickup on the 4 and 6 plug wires when idling; if the light flashes the plug is firing. (Though the plug-out-of-the-cylinder test is pretty reliable, so they are probably still firing in the cylinder.)
That does leave compression. So do a compression test. If it fails that, in addition to a head gasket you could have a valve not closing, one that's too worn, a broken ring .... Try to avoid jumping to conclusions about WHAT is causing your test results.
And do yourself a favor; lay off the "3BLOW" perjoratives. You're working on a 26 year old truck. A head gasket that lasts even half of that is working pretty hard.
The paper test, as you said, [This was to look for a leaking injector, but you can use it to check for opening.] Pressurize the rail via the FP connector, and momentarily ground the white wire by back probing. That should open all three injectors, and the ends of the paper slips will show that.] and it did show the injectors opening because the ends of the per were wet with fuel.
I know it's an old truck, it has 247k miles on it, so if it has lasted this long it's a good vehicle. I just been reading it isn't uncommon to have headgasket issues, but everything has it's problems so it is what it is.
Is there any sure fire way to tell if the headgasket is blown?
I'm going to do the compression test and see what it shows, if it's lower compression between 4 and 6 I would suspect that may indicate a blown gasket between the two cylinders.
It is sounding like I am going to have to take the head off that one side, so I will most likely take the heads off and get them reworked and have a look at the pistons and cylinders and replace cam seals, timing belt, etc..
Ok, guys I checked the compression and I have about 150 on all the cylinders except 4 and 6 (my problem cylinders) those two have about 30! Could the head gasket being blown cause that significant drop in compression? I am working on getting the heads off so I can inspect them, but how would I go about checking the rings to make sure they aren't the problem, or at the least part of the problem?
The "old school" way to check the rings is to add a tablespoon of oil to the cylinder, then check for compression. Supposedly, the oil seals up the rings, so if your compression goes up (to normal?) the leakage is through the rings and not gasket/valves/etc.
The "new school" (??) way to check that is with a leak-down tester. https://www.harborfreight.com/cylind...ter-62595.html With the cylinder pressurized, you listen for where the air is coming out (exhaust, intake, oil-filler, radiator, ...) (Remember: the absolute number you get on the leak-down tester is meaningless; it's only useful for comparisons.)
There isn't much to rings, though. Removing the cylinder heads is in your future, and the inside of the cylinder bores should look pretty uniform (on mine, I could still see the honing pattern). If you see a big oily streak (or scarred cylinder wall), then it's probably a ring.
07-25-2017, 06:41 AM
