chainbrain01

I have a 94 4runner with 240k that died while driving home last night. While driving up a small hill (driving 45mph) the engine stalled out almost like it was starved for fuel. At this point I had to tow the truck home because it wouldn't start again. The battery light is now on when I try to start it.

I just replaced the fuel filter today hoping that was the problem, tried starting it and still won't start. I just replaced the starter last weekend so it cranks fast and strong but the engine won't turn over at all. After a few tries to start I could smell gas in the engine bay so I'm pretty sure it's getting sufficient gas now. I'm at a loss at what to do next to get this truck running now...

Could bad spark plugs cause a 4runner to just die while you are driving? And if so would it cause the battery light to come on as well?

old fart

What size engine do you have, 4cyl? 6 cyl?? And by any chance did you happen to notice the engine temperature after it died? anyways, 1st things 1st, you need to check for spark, make sure your getting spark to all cylinders. If you are smelling fuel strongly, after cranking, it would seem your fuel pump, filter is fine, along with your injectors. Edit: Check your oil yet? hopefully it's still nice and golden brownish/black, and not milky.

chainbrain01

Its the 6 cyl engine. The engine temp was within the normal range when it was running and at the point of when it died. The oil is a dark brown almost black, not milky.

As far as the sparking goes I pulled a plug from each side (one at a time) and tested them for spark but couldn't get a spark while the engine was turning over. Last night I started from the repair manual and started tested my way back through the electrical system. I'm getting 12v to the coil and plenty on the other side of the coil (within range from the manual). I then did a resistive test on the wire from the coil to the distributor cap and it seemed fine. Tonight I just tried a spark test on that same wire from the coil to the distributor cap but I couldn't get a spark while turning over the engine. I double checked my ground point and was able to get a full circuit from the battery to the ground so no problem there. What else could cause it to not spark at this point?

On another note I'm not smelling the fuel strongly after cranking the engine...

scope103

Could be the igniter.

I don't know how you're checking for spark (holding a plug against the block does work, but it's clumsy and dangerous). The easy way is using the inductive pickup on your timing light. A timing light is $20 and you need one anyway.

thedrewski86

I usually check spark w a spare plug against a ground, may be clumsy but it does work. Check for fuel too. Just pull the 12mm bolt from the hard line to the rail. Crank or jumper the fuel pump and look for a fuel shower. Cleans the engine bay out nicely!

Gamefreakgc

You must really like timing lights scope! Seems like every other post is recommending one haha. They do come in handy though.

If you don't have access to a cheap timing light, there's a tool I have and use that you lay along a spark plug wire. When volts are sent through to the plug, it briefly flashes. Got it from Autozone, I think every auto parts place will sell one. Was like $5.

If you think you are not getting spark, check your cap and rotor on top of the distributor. These don't last forever. It fixed my non-start issue a few years back. It'll be obvious, the contacts or the rotor will appear worn or rusted.

RJR

OK, if you don't have spark on the wire from the coil to the distributor, it's not going to run. Forget about fuel filters, fuel rails, spark plug wires, and the distributor and focus on why there's no spark from the coil.

(See the attached wiring diagram. )
The coil needs 12 volts on the + terminal, and a switched voltage from the ignitor on the - terminal. If you're measuring a solid 12 volts on the - terminal of the coil while cranking, that means the ignitor is not firing. It could be either because the ignitor is bad, or the ECU is not sending the "fire" signal to the ignitor. Check pin 21 of the ignitor while cranking. It should show a variable voltage between 0 and 12 volts (it's actually a pulse train better observed on an oscilloscope, but you likely don't have one of those). If it's stuck at a fixed level, it probably means the ECU doesn't think all systems are "go" for ignition. At this point you'd have to dig more into the FSM to figure out which sensor is telling the ECU to hold off.

ign.pdf

oldblue

if your timing belt broke, you won't get spark because the rotor isn't turning to distribute spark. take off your distributor cap, crank engine and see if the rotor turns. if not, time to pull a cover and find a broken belt. do this before wasting a bunch of unessesary electrical diagnosis.

oldblue

i see you said no spark from coil wire to distributor. i'd still check for a broken belt, i may be wrong but i think the distributor still has to turn to send a signal to ignitor for it to fire coil.

chainbrain01

Ok, I pulled the distributor cap off and the rotor turns just fine when I crank the engine. Plus I've taken off the oil filler cap and noticed the cams turn when you crank the engine so that rules out the timing belt I'd think.

@RJR - I've checked the + of the coil and it's reading 12v. I tried to look at the - side while cranking but my multimeter just reads -.10 during cranking. I don't have access to an occiloscope so I can't fully test this... What do you mean by FSM?

chainbrain01

Parts replaced to date:
Fuel filter - old gas looked brown coming out of the old filter...
Distributor cap - old one shown fair wearing.
Rotor - old one was really worn
All spark plugs - Old ones were trashed!

Hopefully I can get my no-runner back to a 4runner!

oldblue

do you have a test light? if so, check to see if it's flashing on the - side of the coil when cranking indicating the ignitor is allowing it to fire.

RJR

OK, here are some voltages I took off my vehicle while it was idling. Your cranking voltages should be similar, except lower.
- positive side of coil -- 13.8 volts
- negative side of coil -- 12.8 volts (The one volt drop from the + side indicates that the ignitor is pulsing the coil to ground at about an 8% duty cycle)
- pin 2 of ignitor (blue/black wire) -- .8 volts. (this comes from the ECU and indicates a positive pulse of about an 8% duty cycle)

Check pin 2 of the ignitor, to see if the .8 volts or so shows up there. I'm guessing it will. If it does, I would say it's likely you have one of two problems.
- An open primary on the coil. Pull the connector off the coil and measure the resistance from + to - on the coil itself. It should be a few hundred ohms, I'd guess. If it measures an open circuit, the coil primary is open.
- A blown ignitor. With the connector off the coil and the ignition off, measure the resistance to ground at pin 5 of the ignitor. If it's a dead short the output transistor on the ignitor is blown.

If you don't get any voltage, or a stuck at 12V voltage at pin 2 of the ignitor, the problem is probably in the ECU or the wiring from the ECU to the ignitor.

(BTW, FSM stands for factory service manual. Here's a link. http://personal.utulsa.edu/~nathan-buchanan/93fsm/)

Let us know what you measure, and we can go from there.

chainbrain01

Ok, just got done testing the coil and ignitor... The + side of the coil is reading the 12 volts and change, the negative side is reading zero while cranking.

Then I checked the pin 2 of the ignitor and I'm not getting any voltage on that wire (black wire with a blue stripe). To eliminate the actual wire I traced it back to the ECM and pushed my lead into that wire where it meets the plug in the ECM and I'm still not getting any voltage read. To check the ground I found the "hot" wire in the far plug and read a full 12v.

At this point do you think I need to replace the ECM? Could there be any other inputs into the ECM that would cause the ECM not to signal for ignition? I'm contemplating biting the bullet and buying a new ECM from my local parts store and hope that solves the problem. Any thoughts are welcome at this point...

RJR

Before you buy an ECM, make the resistance measurements I mentioned in my previous post to rule out a bad coil or ignitor. Also pull off the connector to the ignitor and measure resistance to ground on pin 2 of the ignitor.

RJR

Here's a link to a detailed description of how the Toyota ignition system works. The V6 engine has the ESA system, I believe.

Www.autoshop101.com/forms/h23.pdf

RJR

Based on the article I linked above, 0 volts on the input to the igniter should result in 12 volts on the output, assuming the coil and igniter are good. The fact that you're seeing 0 volts both places suggests either an open coil or a bad igniter. Definitely remove the coil connector and check the primary resistance. It should be around an ohm.

oldblue

i may be leading you the wrong way, but i think i'm pretty sure this is how you should check this. correct me if i'm wrong.

the negative side of the coil won't have voltage ever. it is a ground. the ignitor is what grounds the coil to give the primary side voltage which allows the secondary side to saturate and produce the high voltage spark. thats why putting a test light on the ground side with the lights cable hooked to your positive post of your battery and the probe on the negative side of your coil. if it flashes, the ignitor and pickup inside the distributor are working correctly. the pulse is too quick for a voltmeter to read. old school stuff, but its way faster and simpler than tracing wires and checking resistances and such.

RJR

The test light is a good idea, but your explanation of how the system works is not quite right. The negative side of the coil spends most of its time at 12 volts. Then, a few degrees before a spark is needed, the igniter pulls the coil to ground so that a current builds up. At exactly the right time for the spark, the ECM tells the igniter to interrupt the coil current. This generates a high voltage in the secondary creating the spark, which is routed to the correct plug through the distributor.

The negative going pulse on the coil is always roughly the same length, because it's the length of time for the current in the coil primary to build up to saturation, and that's determined by coil inductance and battery voltage, which are relatively constant. So, at cranking speeds the pulse will be relatively very narrow, and the voltmeter will show a coil voltage near (but not quite at) 12 volts. A typical handheld DVM averages the voltage over perhaps .2 seconds or so, so while it won't accurately measure the pulse, you can detect its presence. (Some quick calculations based on measurements made on my truck suggest the pulse is about .002 seconds in length at idle.)

Under no circumstances should the voltage at the negative terminal of the coil measure near ground, especially at cranking speeds. That would imply 10-20 amps going through the coil, which would get it very hot and likely burn it up fairly quickly.

scope103

Good explanation. This site http://www.autoshop101.com/forms/h23.pdf suggests that the length of the negative going pulse (dwell angle) is controlled by the igniter (longer at higher engine speeds, shorter at lower speeds to reduce coil heating.)

This isn't going to make much difference to the kind of testing I can do; my oscilloscope uses line power, so I can't watch the dwell angle at speed. Fascinating nonetheless.