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My 97 4runner 3rzfe engine backfiring I hear from inside the…

My 97 4runner 3rzfe...

My 97 4runner 3rzfe engine backfiring I hear from inside the hood.

Mechanic's Assistant: Where exactly do you think the noise is coming from? And how long has this been going on?

I think from air intake or manifold. I have the 4runner since and had 1st time to experience it. Just last week.. suddenly stalled while on a stop engine idling.. now backfiring and you can smell unburnt fuel thru the exhaust.

Mechanic's Assistant: Are you fixing your 4Runner yourself? What have you tried so far?

Yes.. read fora watched you tube.. Changed spark plugs yesterday.. initially improve engine run.. then added total fuel system additive to a full tank this morning.. seems okay thenbackfire became worser and stalling.. funny nis that idling is very smoothj.

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

When I changed spark plugs, I notice the plug wires were sort of wrappep with electrical tape.. should I consider chjanging the wires?

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Answered in 11 minutes by:
2/26/2018
Matt
Matt, Mechanical Engineer
Category: Toyota
Satisfied Customers: 23,488
Experience: BEng, Repaired my own cars and others for 20 years, worked in Formula 1 for 10 years
Verified

Hello and welcome to Just Answer

I'd definitely replace the wires if they've been repaired with tape

Check the resistance of the spark plug leads ( 13-15Kohm / metre) and replace if any doubt or high resistance - Also replace the spark plugs if any of them fail this checklist:

https://www.ngksparkplugs.com/about-ngk/faqs/spark-plug-faqs/how-do-i-read-a-spark-plug

also check the condition of the engine earth / ground connections as they need to be tight and corrosion free at both ends

there should also be a small earth wire that runs out of the loom and is secured to the engine

this is the ECU earth connection and also needs to be tight and clean

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My goal is to give you the best advice that I can and I hope that I've helped today. Please remember to rate my service by selecting from the 5 stars at the top of the screen before you leave. If you need more help, use the reply box to let me know.
If you're not pleased, also let me know because rating bad does not result in a refund, there are better options. Rating now will not close this post nor prevent further replies
Thanks Matt

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Customer reply replied 5 months ago
Hi Matt,
Thanks ..
May I request photo, if possible, of the earth connections... both the engine and ECU/ECM..
Should I proceed with changing the fuel filter and the MAF?
As you know, Iwill have to order this parts thru EBAY or Amazon since these parts are not available / difficult to source in my country.
thanks

Hello

the engine connections can be found by following the large battery cable back from the battery to the engine

and I'd 1st replace the ignition parts and then clean the MAF with some solvent

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Customer reply replied 5 months ago
Okay..I have followed removal and replacement of spark plug wires at you tube.
When I do this, I will be removing some interfering parts and I will have the opportunity to clean the manifold.
should I clean this too?
Customer reply replied 5 months ago
Also..
you said to replace the ignition parts..
Any advise non the ignition coils?
Customer reply replied 5 months ago
PS..
I prefer to submit my rating after I do some initial corrections per your expert advise..
Thanks.

Hello

start with the wires and you can also try spraying some water on the coil packs with the engine running. It is possible the coil is faulty and causing the misfire. If you see sparks arcing with the water, then replace the coil.

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Customer reply replied 5 months ago
Hi Matt,As I said, I have replaced the spark plugs.
Am ordering a set of spark plug wires thru Amazon.
Will see if it will solve the backfiring.
Till then.. on what basis should I rate you?
Speed of response only?RS Joya

Hello

only rate when you are satisfied

if new plugs and wires doesn't help with the back firing then check the coil packs a I've suggested and this could also be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out causing rough running.

As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propaneor brake cleaner around each joint in turn. If the engine rev's up you've found your leak.
Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

Air leaks are very temperature dependent as gaps can open up as things expand with temperature so depending on how the leak occurs ( on a hose joint with a clamp expansion will help seal and on a vacuum hose expansion will make a leak worse) so leaks can be better or 1 vacuum leak path that you won't find with the above test is if the brake servo is leaking

so try clamping off servo hose to see if this has any effect

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.
if the engine condition is the same then chances are the meter or the connection to it is faulty

It’s also worth cleaning the MAF sensor wires, as they can get coated with dirt over time which then offsets the reading
Use some contact cleaner or brake cleaner to spray onto the wires to remove the dirt – on no account touch the wires with anything as they are very fragile

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Hi
do you still need help?
Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! If you're not pleased, also let me know because rating bad does not result in a refund, there are better options. Rating now will not close this post nor prevent further replies
Thanks Matt

Matt
Matt, Mechanical Engineer
Category: Toyota
Satisfied Customers: 23,488
Experience: BEng, Repaired my own cars and others for 20 years, worked in Formula 1 for 10 years
Verified
Matt and 87 other Toyota Specialists are ready to help you
Ask your own question now
Customer reply replied 5 months ago
Hi,
I have ordered a tune up kit and a MAF..
Will try to do your suggestions.
Waiting for its arrival and will info you of any results.
In the meantime, I will rate you without any evidence on how accurate those are.
Thanks.
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