How to diagnose the cause of no power reaching the spark plugs when power reaches everything else, after checking fuses?

Question

I've been trying to get my long-suffering Toyota RAV4 first generation (1998) to start after numerous different problems, the latest of which I've narrowed to the spark plugs not firing seemingly due to no power reaching the spark plug wires.

So, my next problem is figuring out why no power is reaching the spark plug wires:

• I've checked all the fuses (even ones unrelated to the problem), and tested them all with a multimeter even when they look fine.
• I've checked and tested the main relay out of the car (though I guess it's possible there's a problem with the connection to and from the relay?)
• The battery, starter motor, dashboard, fan and fuel pump all appear to be working fine
• The spark plugs themselves are new, don't appear to be damaged (though I'm not exactly qualified to judge). A little bit grimey, maybe, but doesn't appear to be enough to cause a problem
• The "check engine" light doesn't come on while I'm trying to start the car. I know in some models, this indicates no power to the ECU, I can't find confirmation whether that's also true for old RAV4s (and I can't remember if it came on when starting the car before). Nothing in the owner's guide or that I can find online.

I've got an electrician coming to look at it, but I've been warned by many car owners who've been in this country (Sierra Leone) longer than I have that car electrics is the biggest skills gap the largely self-taught local mechanics have, something I've seen evidence of already, e.g. none have been able to make any progress at all with this dashboard problem, and I've found many worrying things like blown fuses "fixed" by wrapping copper wire around the connections (I replaced all these immediately!).

I'd like to at least be able to do some investigation of the problem myself and if I can't solve it myself at least be in a better position to supervise.

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Update: I think I've fixed the original problem that was causing me to check the power to the spark plugs, but it's absurdly specific to the hazards of car ownership in a 3rd-world country, so it's not likely to be much help to most people interested in this sort of diagnosis! The details are here on my answer to my original "car won't start under strange circumstances" problem (basically, the fuse socket's connection to the ignition system was lost due to bits of broken copper wire stuck deep in the socket, from an earlier broken fuse having been "fixed" with wire under a previous owner).

Answer 1

If you've established that you're not getting a spark at the plugs, the next thing to do would be to work back - so test the coil packs. Pull out the plug from one of the coil packs and see if it is getting power, has a good ground, and has some kind of signal coming from the ECU. If it does, chances are it's the coil pack itself that's failed (though both failing at the same time seems unusual). You'll need to find a pinout of the coil or a wiring diagram for the car to work out which pin is which.

If one or more of those are missing, at least you'll have a better idea of where to look...

Answer 2

Rule of thumb: 1. always check fuses first. If fuses are okay, then check relays [those are the silver 'fuses' in the fuse harness. 2. all okay? 3. check major relays under the hood. These are generally box-shaped black plastic with larger wires coming out of them. These are major problems in older cars because of the heat and moisture generated over time. 4. relays okay? Finally, check the distributor...even fuel injected cars have a distributor system to send power to the plugs correctly. Distributor okay? 5. take this beast to the mechanic. Make sure he/she is someone used to tracking down electronic problems in automobiles. You say it's a Rav 4 so it really is not that complicated, but when dealing with electronics it is very difficult some times to track down the problem let alone fix it.

Answer 3

If it is a 1.8liter L4 DOHC (1 zz series X) Toyota engine (which 90s Rav 4s are) you do not have a distributor because it is an integrated system within the throttle body. Check your airbag system along with the firing order your spark plugs are in. You'll find all different firing orders even in a Haynes manual but having seen the valves of one of these myself it is 1-3-4-2 over the twin coil packs from the front of car to back directionally and the block order is 1-2-3-4 from left to right standing in front of the engine.

Under your dash is a panel of fuses and relays called junction block 1... Have you verified there? If not do so. You may just be missing necessary ground wires too.

Alldatadiy.com is a place where you can buy a subscription to your type of engine and it should help you with wiring schematic just to verify everything. It provides factory schematics for exactly your engine. Anyway I hope that helps, good luck.