Jhoward

Hey all. Trying to narrow down the issue on my 1995 3.0 liter SR5. Power is down and feels like It’s down a cylinder. The header on cylinder 3 is not getting hot. All other cylinders water sissles away on contact with header pipe. Checked the spark at the plug and it’s strong. Did a compression check on all cylinders except number 5. Values were all between 140 and 150 psi.....engine cold, 180,000 miles. So given good compression and spark on cylinder 3, I’m thinking bad fuel injector or bad signal to injector? Any thoughts appreciated.

Melrose 4r

i think you are on the right track with injector. Any misfire codes?

Jhoward

I haven't done a code check. Can't get it to a shop right now and no code reader at home. I do have an automotive stethoscope..sounds like I can use that to listen for the injector making a constant clicking sound before I pull the intake? Should tell me whether it's working or not? If I can access that area.

scope103

There are no 'misfire' codes.

Before I started "zeroing in" on the injectors, I'd do a "cylinder efficiency" test. All you do is pull the spark plug lead on #3; does it change the way the engine is running?

Jhoward

Pulled the wire on cylinder 3...no change in RPMs, tone or symmetry. You can hear and feel the miss with the wire on or off. I feel 90% certain there is nothing combusting in the chamber. I’m 99.9% certain I’ve got good spark through the plug and my compression check shows close to 150 psi on the cylinder. Could it be anything other than the injector at this point? Intake valve not opening? Is that an option? Thanks for the input on this.

Melrose 4r

If your intake valve wasn’t opening, you wouldn’t have a good compression test on that cyl.

Jhoward

Gotcha. Figured that might be the case, but wasn’t positive.

scope103

How did you check the spark? If you used the 'ole-reliable' method of holding the plug against the block and cranking it, you might consider putting the plug back into the head, and using your inductive pickup on the lead see if the plug is firing (flash => firing). This doesn't add much (the ole-reliable method is pretty good), but it's pretty easy to do before you start real work.

Also, check for stored codes. You don't need (and don't benefit from) a "code reader". http://web.archive.org/web/201211190...85diagnosi.pdf (The "SST" is a paper-clip.) A persistent miss can set code 26.

Other than that, my next guess is an injector issue. But before I pulled it out, but after I removed the plenum, I'd inspect the wiring. (through my own fault, I once pulled the wires out of the plug to the injector). The injector is opened with just battery voltage, so put 12v (briefly!) on the terminals and you should hear a click. If it won't click, it may be a bad injector. If it does click, I'd try to confirm that you're getting 12v on one injector lead, and the other pulls to ground on cranking (there is constant battery voltage on one lead with key-on; the injector opens when the other lead is pulled to ground).

Jhoward

Thanks for the link. I’ll check for stored codes just in case before I pull the intake. I did use the old school method to verify the spark...strong snapping. Pretty sure I’ll be pulling the intake up this weekend, if not sooner. Wasn’t sure how to verify voltage reaching the connector, but now feel confident checking that. I’ll keep updating on my progress.

Jimkola

I'd think if there was no spark in the cylinder than the plug out to be fairly wet. If the plug is dry, and getting spark, I'd lean towards a faulty injector or wiring. Ever get rodents nesting?

Jhoward

Yea, I’ve had the plug in and out several times. It’s staying dry. Strong spark on plug when grounded to block. Found a snake skin under the hood, but no evidence of rodents.🐀

Jimkola

I'm always hesitant to condemn an injector, the Denso injector is remarkably durable. But they do fail or get clogged from time to time. I was just wondering if the wiring to that injector may have been damaged or gnawed on.

Co_94_PU

iTrader: (-1)

Open your FSM, find the injector check page that gives individual OHM values. Find convenient place upstream to connect a multi meter, I don't think the 3vze ever had the convenience of a resistor did it, unplug ECU and read resistance on #10, #20 now multiply by six to get average injector resistance. If you have an open coil or circuit in the #3 injector this will point it out.

You can also try current measurements, one injector vs #10&#20 at the ECU, you should have close to six times the individual current..

scope103

Hard to imagine that would work. The FSM spec is 13.4-14.2 ohms, so you'd be looking for the difference between 80.4 (6x13.4) and 71.0 (5x14.2) ohms. Jamming DMM probes into a connector could easily produce more than 9 ohms difference. Throw in a modest increase in resistance in the 25-yr old wiring ...

I understand the desire to avoid removing the plenum, but based on jhoward's otherwise careful diagnosis I don't see much way to avoid measuring right at the connector to #3.

Co_94_PU

iTrader: (-1)

Whoops error, it's total * count = individual. So 13 / 6 ~= 2 ohms.

We do this sort of comparison all the time, you're looking for a consistent number and if you need to average them you do and throw out any anomaly that's more than expected or doesn't match your other tests. This eliminates "oops I touched it" and "well that was a bad connection".

The current one is even more finicky =P

But it gives you an idea of what you might find before you get in there, so maybe you know you've got to replace an injector and have one on hand.

scope103

Oh, gee, I made the same mistake.

To find an "open" injector you'd be looking for 2.68 (13.4/5) vs. 2.37 (14.2/6) ohms. Well beyond the resolution of any hand-held DMM, and even pushing the accuracy of 5-digit lab ohm-meter with a 4-wire (Kelvin) connection.

Jhoward

In all honesty, what I’ll probably end up doing is replacing the suspect injector with a new one (arriving from Rockauto Sat. Or Mon.). Visually inspect the injector wiring and plug for anomaly’s and then rebolt the plenum And see what I’ve got. I’m a big fan of the more “correct and thorough” method, but my electronic testing skills don’t go much above a 12 volt test light. As unlikely as it may be that an injector would go bad, doesn’t it seems even more improbable that the wiring would fail? I do appreciate every response and all perspectives on this.

Jhoward

Based on one of Scopes posts, it sounds like I should be able to find a ground pulse at the connector with the test light to verify the signal is reaching the injector?

scope103

You "should" be able to detect the ground pulse (the lead gets pulled to ground by the ECM) while cranking. The pulse isn't very long (milliseconds), so I don't know if you could pick up the short dip in a regular test light ("noid" lights are designed for that purpose; they may have smaller bulbs). I'm pretty sure you could pick it out with a 12v LED; if you don't have a "pre-made" 12v LED all you need is a 1k ohm resistor in series with a regular LED. DO remember that LEDs are polarized.

A lot of this advice about testing the electrical side is to avoid removing the fuel rail and the injector. Whenever your remove any of the "banjo" pressurized fuel connections (you'll have to remove a minimum of 3, more likely 5, to lift a fuel rail) you must replace the 3 (5) pairs of crush washers. They are one-time-use. Cheaper than dirt, but I've only found them at the dealer. If you remove an injector from the rail, you must replace the o-ring at the injector-rail connection. You should also replace the upper and lower grommet, and the pintle cover. E.g.: (the terminology of all the grommets, o-rings and spacers is inconsistent, even in the FSM). Your new injector ought to come with all of these; if you can successfully lift the rail with the injectors in place you may be okay with the rest of them.

I'm no expert on this, but if you really have only one injector not opening (and that diagnosis is not yet certain), I would still suspect the wiring before the injector. You can almost test the injector in-place by listening for the click when you apply 12v. The limitation on that test is if the single injector is working but clogged. There is a filter screen at the entrance (you can see them in the Amazon listing I linked), but you'll have to remove the injector just to see it.

Having said all that, I should mention that there is a reliable in-place test. With the fuel connections all intact, you only need to add a line (6mm / 1/4" vinyl tubing) from the fuel return on the pressure regulator back to the fuel return line near the firewall. Then you can run the fuel pump with the FP to B+ connection. With the rail pressurized, apply 12v to see if the injector sprays. How do you tell? Cut a strip of paper 1" wide and slide it down the open lower intake manifold so the end is under the injector. If the injector sprays, the paper will get wet (check the paper before you apply 12v; you can detect a leak that way.)

Good luck!

Jhoward

Thanks for all the great tips. I forgot all about the crush washers. I'll order them from the dealer Friday. I'm really digging the in-place injector test...I can definitely handle that. I'll do the injector test next Monday and post my results here. Happy turkey day!