Engine misfires briefly and then after five to ten seconds returns to normal idling

ANASTASIA9

MEMBER
1996 TOYOTA PREVIA
147,000 MILES

If I brought in a 1996 Toyota Estima, wide body, Supercharged with 147,000ks in excellent condition, extremely well maintained and said “the symptoms were when you start engine in the morning, engine misfires briefly and then after 5 -10 seconds returns to normal idling. Doesn’t happen when driving and that I’d phoned around and canvassed a few opinions as to possible causes and was told subject to viewing and inspecting, the verdict appears to be either distributor or leads, spark plugs, inlet manifold, rocker cover gasket leaking, or head gasket problem, but as the distributor leads were done recently, they can be eliminated. So could you please diagnose the problem, ” how would you proceed to diagnose the problem and what would you do?

Tuesday, April 20th, 2021 AT 4:57 PM

3 Replies

JACOBANDNICKOLAS

MECHANIC
110,125 POSTS

Hi,

First, this vehicle isn't offered in the US, so I have little technical info. However, I will try my best

If this only is happening on a cold start, the first two things that I would question would be either the need for a tune-up (worn plugs) or there could be a fuel injector leaking down when the engine sits. That would cause one cylinder to misfire until it burns the fuel off.

The other issue, which is also related to fuel, is the coolant temperature sensor. If it responsible for signaling the computer the temperature of the coolant. Then, the computer decides (based on that reading) how rich or lean the fuel mixture needs to be for starting.

Here is what I suggest: The easiest thing to do is remove the spark plugs and inspect their conditions. If they are worn, replace them.

Next, check the fuel pressure. Specifically, watch fuel pressure drop off. If it drops fast, there could be a faulty injector bleeding off. Here is a link that shows in general how it's done:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

As far as the temperature sensor, if you have access to a live data scan tool, before starting the vehicle, check the signal from the sensor to see if it is close to the ambient temperature.

I hope this helps. Let me know if you have other questions.

Take care,

Joe

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Wednesday, April 21st, 2021 AT 8:04 PM

ANASTASIA9

MEMBER
2 POSTS

Thank you very much for your response. It is appreciated. Just expanding the question a little further as follows: "Started with misfiring in morning when starting vehicle for the first time for the day lasting for 4 � 5 seconds, which slowly began to increase in duration over time to about 10 seconds. Then it began to start happening throughout the day when the vehicle had been parked for longer than about 2 hours and I noticed a slight loss of power when going up a hill � but only slightly. Then it was beginning to give off very strong acidic fumes and a little greyish exhaust fumes. If I brought this vehicle in to have the problem fully diagnosed then repaired, what would your approach be as a professional?

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Wednesday, April 21st, 2021 AT 10:33 PM

JACOBANDNICKOLAS

MECHANIC
110,125 POSTS

Hi,

First, I would check codes to see if there is a specific cylinder with a misfire or if it is random. If it's specific, then I would check plugs, coils, and so on.

If there are no misfire codes, then I would check fuel pressure. The idea that you are seeing gray smoke could indicate a rich fuel mixture. Plus, the smell you described could be related to this as an issue as well. Usually, black smoke is noticeable when the fuel is rich. White smoke could indicate coolant being burned, so I would (and don't laugh) take a good smell of the exhaust to see if I could recognize it.

Also, a rich fuel mixture can be caused by an engine coolant temperature sensor (ECT). I would confirm the sensor's signal aligns with ambient temperatures.

If nothing pans out with any of those things, I would be checking fuel trims to see if there are any indications of a fuel mixture issue.

Does that help?

Joe

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Thursday, April 22nd, 2021 AT 7:10 PM