Question about 1998 Toyota RAV4
There are lots of things that can cause this. It could be electrical, fuel, or compression. I would start with running a compression test. Are the cylinders even and in a normal range (different gauges, temperatures, and ambient conditions can cause the readings to vary a lot, but they should all read within about 10 lbs. of each other). All the same within a small margin is more important than the actual reading unless that is really low. If they do read even, you have eliminated a lot of possible causes. If they don't then you should start with the simplest of possible reasons before getting drastic. You said the head was recently rebuilt with helicoils, so start with: Check valve adjustment. It isn't unusual for a valve to be maladjusted after replacing the head and driving a couple thousand miles. I'm sure you had the cam shaft checked out when you did the head, but if not, that is another potential source. An ill fitted helicoil will also do it. All of these will show up on a compression test. Unfortunately, it is not unusual after a valve & head gasket job, to discover that the increased compression from that exposes some leaky compression rings that were masked by the previous poor compression. This isn't likely, but it is possible and a "worst case" scenario. (Assuming the head and valve job was done correctly). If you do find a low cylinder, you can determine where the leak is by setting that cylinder at top dead center on the compression stroke and charging the cylinder with compressed air (or nitrogen), then listening to where the air is leaking from. If it is coming out the exhaust, it is an exhaust valve, out the PCV then it is rings, intake manifold - intake valve.
If the compressions are all even, then it is either fuel or electrical. The first thing I would do is switch the plugs to different cylinders. Is the miss still with the same cylinder? Even new plugs are occasionally defective. If the problem moves, then check that the plugs are the correct plugs and they have the correct gap. Many Japanese engines are very picky about their plugs. Hondas are more picky than Toyota, but stick with NGK or Denso and you are likely to be OK. Is your engine one where there is a separate coil for each cylinder or a "standard distributor"? I can't remember when Toyota started that, but if your engine has the coil for each cylinder arrangement, a coil is a likely culprit. It could even be the ECM.
You said the plug wires were good. Did you ohm them out or just visually inspect them? They have to test for proper resistance and not just look good and make good contact.
If you eliminate electrical, it could be an injector, a carbon'd up intake manifold or intake valve (although this would probably show up in the compression test. As you recently had the head off, I am sure you cleaned the intake manifold before reassembling so this isn't likely either.
When you do find the problem, please let everyone know what it was.
Posted on Mar 21, 2014
Testimonial: "Hi Robert Grove the head replacement was done by a mechanic it is a new head, One would think that he did all the necessary tests (at least he charged me for them) the car came back with a slight flat spot I returned the car to him after 7 hours of diagnosis he was unable to determine were the fault was. suggested fuel injector cleaner then sent me on my way. I found the car was using excessive oil but no visible signs of a leak nor smoke. I am about to change the coil pack as tests have show the HT leads and spark plugs are fine. I thank you for you input and will get back to you. BTW the mechanic does not seem to be interested in helping me with this problem. He is located some 200 kms for me as the head let go out near him to have the car towed to him will cost over $600.00 cheers David"
David, if you have changed the plugs and HT plug wire/caps have you checked the ignition coil for no. 2? It could be breaking down and not delivering sufficient voltage. If the problem persists then you need to do a compression test to see if no.2 has comparable compression. If it is low take the radiator cap off with the engine running, (being careful not to burn yourself) and look for bubbles in the radiator water. Check to see that the engine oil on the dipstick and under the oil filler cap is not creamy. If you have bubbles or creamy oil you have either a cracked head or leaking head gasket.
Posted on Mar 20, 2014
Also is your Coolant or oil level low after driving? Does your spark plug look like there is lots of white or black deposits on it? These indicate mechanical problems in the cylinder.
Posted on Mar 18, 2014
I had before a miss fire ,
it had been solved with me by Changing The wires that Connecting the Sparks
Posted on Mar 18, 2014
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Posted on Jan 02, 2017
see your basic elements for your car to have a spark is your coil ignition module condenser in some of the cases your computer is not sending a spark signal. so check your ECM wiring
Posted on Jun 20, 2008
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