Mystery....Need engine experts.

[Former_Jeeper]

Ok so about a month ago the 4runner (99 3.4L Auto 150k) started shaking really bad but only at startup and only for about 10-15 seconds. So naturally as a somewhat mechanically inclined person I

Cleaned MAF sensor, replaced air filter, Replaced IACV valve, cleaned throttle body, replaced PCV valve, grommet, and hose. Replaced spark plugs with Proper OEM as well as NGK wires.

Shake did not go away as i thought it would. No codes have been thrown during this mystery also. Once the shaking stops it is smooth as butter for the remainder of the drive.

Fuel filter is relatively new. All 02 sensors are newish and proper Denso units.

I have used propane to search for vacuum leaks and did not find any, replaced some vacuum hoses as well (just to be anal).

Some of you have no doubt concluded maybe a headgasket. However, oil looks clean and radiator is full, no smoke or sweet smell out of the tailpipe.

So now I am stumped. Hopefully I missed something small that someone else can help me solve this mystery as I am about ready to take to a shop so they can charge me a ton of money only to replace stuff that doesnt need replaced and not fix the problem lol.

Thanks in advance.

 

[Dieselchessy]

I had similar symptoms. Replacing injectors resolved most of it. My next plan is to replace the fuel pump and screen.

 

[sleepydad]

Ok so about a month ago the 4runner (99 3.4L Auto 150k) started shaking really bad but only at startup and only for about 10-15 seconds. So naturally as a somewhat mechanically inclined person I

Cleaned MAF sensor, replaced air filter, Replaced IACV valve, cleaned throttle body, replaced PCV valve, grommet, and hose. Replaced spark plugs with Proper OEM as well as NGK wires.

Shake did not go away as i thought it would. No codes have been thrown during this mystery also. Once the shaking stops it is smooth as butter for the remainder of the drive.

Fuel filter is relatively new. All 02 sensors are newish and proper Denso units.

I have used propane to search for vacuum leaks and did not find any, replaced some vacuum hoses as well (just to be anal).

Some of you have no doubt concluded maybe a headgasket. However, oil looks clean and radiator is full, no smoke or sweet smell out of the tailpipe.

So now I am stumped. Hopefully I missed something small that someone else can help me solve this mystery as I am about ready to take to a shop so they can charge me a ton of money only to replace stuff that doesnt need replaced and not fix the problem lol.

Thanks in advance.

for the engine to run we need timing, spark, and fuel.

It sounds like you are confident you have timing and spark.

I'm going to toss out a wild guess and say fuel pump. If it's consistently rough @ start up. what if you leave the key in the on for 20 seconds then crank to start?

I guess I would want to know what the fuel pressure is but that is probably something you will have to pay to find out unless you already have that setup with a fuel pressure gauge.

<a href="https://imgur.com/jyc61pA"><img src="https://i.imgur.com/jyc61pA.jpg" title="source: imgur.com" /></a>

 

[Dieselchessy]

Far as I know the fuel pump on these don’t pump until the computer sees the engine turning.

 

[brillo_76]

Far as I know the fuel pump on these don’t pump until the computer sees the engine turning.

Correct. Until the starter engages the fuel pump is off. Hence why cold starts crank almost 2 seconds to start.

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[Former_Jeeper]

Thanks for the replies.....

Fuel crossed my mind but it doesn’t have the symptoms I would associate with bad injectors the fuel pump is a possibility but it is only happening on startup.....there is no other stutter or loss of power or other problems associated with fuel pumps.

Not to say injectors/pump couldn’t be the cause anything is as likely to me as the next.

Is it best to just to take to a shop and have them check fuel pressure? Injectors tested?

Anything else I could be missing?

 

[thegipper]

When the head gasket started to go on my truck, my truck would shake for 15 seconds or so before it would smooth out. It also didn't blow any white smoke and only after a few weeks would the reservoir be down about a 1/2" or so. Never had any check engine lights for the shaking until it got really bad and I confirmed it was a blown head gasket.

I tried all of the quick "tests" for checking for a bad HG and all of them said I didn't have a blown head gasket until I did a leak down test. The second I pressurized cylinder #3 I had air bubbles coming out of my radiator.

I'm not saying for certain you have a blown HG but its a possibility. If you want to 100% rule it out or confirm it, do a leak down test.

 

[Bad Luck]

You can't truly eliminate a head gasket issue until you do a compression and leak down test. I recommend doing it on a cold engine since you are having the issues on startup.

 

[Jarods7920]

Definitely do a leak down test and compression test. Also may want to try a coolant pressure test. Based on what i have read, its highly likely a head gasket or cracked head issue with coolant leaking into the cylinder. Mine does this currently and have found no fix for it.

 

[gamefreakgc]

Thanks for the replies.....

Fuel crossed my mind but it doesn’t have the symptoms I would associate with bad injectors the fuel pump is a possibility but it is only happening on startup.....there is no other stutter or loss of power or other problems associated with fuel pumps.

Not to say injectors/pump couldn’t be the cause anything is as likely to me as the next.

Is it best to just to take to a shop and have them check fuel pressure? Injectors tested?

Anything else I could be missing?

There is no good way to test fuel pressure, we don't have a schrader valve so the shop won't be able to do anything unless they remove part of the fuel rails (read as more $$$).

What could be possible is that one or more check valves in the fuel system have failed. It could be the check valve on the pump that holds line pressure, causing a low pressure situation at startup. Or, it could be a failed injector check valve and it's leaking into the engine.

Does the issue get worse the longer the vehicle is inactive?

 

[Vintage Iron]

You can't truly eliminate a head gasket issue until you do a compression and leak down test. I recommend doing it on a cold engine since you are having the issues on startup.

Definitely do a leak down test and compression test. Also may want to try a coolant pressure test. Based on what i have read, its highly likely a head gasket or cracked head issue with coolant leaking into the cylinder. Mine does this currently and have found no fix for it.

Just a thought, FJ - If you don't have a cylinder leak-down setup, there's an old-school way to check this. One evening, after you're through using the vehicle for the day, pull the sparkplugs. Let the vehicle sit overnight. Because the engine is warm, there'll be pressure on the cooling system. By pulling the plugs, you've released any internal cylinder pressure, which creates a pressure difference on the gasket surface. The next morning, crank the engine over while keeping an eye on each cylinder. The spark plug hole spewing a fine mist will be the one with the head gasket leak.

 

[19963.4lsr5]

To me you have a head gasket going bad or a leaking injector causing a flood condition at startup.

A cheep bore-aH-scope looking in each spark plug hole on a cold engine will tell the tale.

Until your engine goes closed loop you’re not going to get any codes.


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[clearock]

There is no good way to test fuel pressure, we don't have a schrader valve so the shop won't be able to do anything unless they remove part of the fuel rails (read as more $$$).

FYI. u don't need a Schrader valve on the fuel system to check the fuel pressure, checking it is not hard and does not require u to remove part of the fuel rail, all u do is disconnect the flared fitting on the driver side (the main connection from the chassis to the engine) and connect here with fittings that allow u to connect a gauge (a good fuel pressure kit has said). u can also pull the fuel rail banjo bolt on the front side of the block (I use the pass side on as it not hard to get at) and use the special banjo bolts with a schrader valve to connect.

 

[Former_Jeeper]

Update

So just to get an idea....I called around to some shops and it’s going to be roughly about 2700-3300 depending on what they find if it is in fact a bad HG. At this point I don’t think I’m able to drop that amount of $$$ on it. So I may get a diagnosis professionally and see if that what it is but I’m having trouble justifying paying that much currently.

I live in Indianapolis IN if someone happens to know of. Guy that can do it somewhat cheaper.

Thanks for everyone’s input. Hopefully it’s just an easy fuel delivery something or other.

 

[gamefreakgc]

There is no good way to test fuel pressure, we don't have a schrader valve so the shop won't be able to do anything unless they remove part of the fuel rails (read as more $$$).

FYI. u don't need a Schrader valve on the fuel system to check the fuel pressure, checking it is not hard and does not require u to remove part of the fuel rail, all u do is disconnect the flared fitting on the driver side (the main connection from the chassis to the engine) and connect here with fittings that allow u to connect a gauge (a good fuel pressure kit has said). u can also pull the fuel rail banjo bolt on the front side of the block (I use the pass side on as it not hard to get at) and use the special banjo bolts with a schrader valve to connect.

Yes, one definitely can be added. But he's taking it to a shop and they won't have all those little bits on hand and will charge an arm and a leg or just flat out say they can't do it.

 

[clearock]

Yes, one definitely can be added. But he's taking it to a shop and they won't have all those little bits on hand and will charge an arm and a leg or just flat out say they can't do it.

if the shop doesn't have the equipment i'm talking about i'd leave quickly as they r basic parts of a master fuel pressure set that any basic shop should have, every shop I've worked at has had 1, I have 2 diff brand name set i use 4 personal use. not trying to bust ur balls, just trying to get the point across that if a shop is charging u a lot just to check fuel pressure then they don't have a clue what they r doing and ur money is better spent else where... even if the shop didn't have the above it's not hard to make an adapter, which a good shop will not charge u 4 their learning curve.

 

[Former_Jeeper]

Actually I know it’s a sin as far as forum members but since this is above my level of wrenching I’m taking it to be diagnosed at a dealership .......not to worry my friend that works there can give me a decent discount plus I figure they are more versed on Toyota specifically as well as oem and not cheap aftermarket parts.

So they should have all the necessary testing equip on hand.

 

[Captsolo]

When the head gasket started to go on my truck, my truck would shake for 15 seconds or so before it would smooth out. It also didn't blow any white smoke and only after a few weeks would the reservoir be down about a 1/2" or so. Never had any check engine lights for the shaking until it got really bad and I confirmed it was a blown head gasket.

I tried all of the quick "tests" for checking for a bad HG and all of them said I didn't have a blown head gasket until I did a leak down test. The second I pressurized cylinder #3 I had air bubbles coming out of my radiator.

I'm not saying for certain you have a blown HG but its a possibility. If you want to 100% rule it out or confirm it, do a leak down test.

AGREE thegipper... I think the HG should be looked into. Any white smoke out the tail pipe (step on the gas peddle and look)? Any white gunk in the filler cap? Bubbles in the radiator with cap removed when running at idle? Coolant level dropping a little every week? :guitar3:

 

[RivMan]

I agree that this sounds like a head gasket or injector problem. Here's how I would diagnose it:

Symptom: Misfire on startup. What's likely happening is that a cylinder is ingesting some fluid (Fuel or coolant) while the truck sits, and when you start it, it's washing out the spark, causing a misfire.

Test:
I'd start with a cold engine and pull each spark plug. Is one completely covered in fuel? Coolant?
Then I'd run a leakdown test with the radiator cap off. Look for bubbles in the radiator for each cylinder.

Good leakdown and no bubbles: Probably injector.
Bad leakdown and/or bubbles: Headgasket.

In my case I had a Cylinder 2 misfire on startup. I suspected a headgasket, but when I pulled the spark plugs, cylinder 2 was soaked in fuel. Leakdown was perfect, no bubbles.

-Rob

 

[Former_Jeeper]

Mystery solved.....



Official diagnoses is a Headgasket.

My friend that works at a dealership is going to have his master technician do BOTH head gasket s and timing belt/water pump also.

$2600 parts & labor

I thought of course about just doing the gasket that’s faulty as well as an engine swap but for several reasons decided against an engine swap as mine besides the gasket is in pristine well maintained shape good for another 200k easy.

I don’t want anymore problems as I have a 3 week old baby at home so I figured might as well get both gaskets done and hit the timing belt and water pump while they are at It and while it has the attention of a dealership Toyota master mechanic who knows what he is doing.

I was hoping for a vacuum leak or leaky fuel injector but wasn’t going to be so lucky.

I figured on a 22 year old engine with bolts that are 22 years old $2600 with my discount done with oem parts at a dealership with a master Toyota mechanic isn’t a terrible price considering $800 is in oem parts.

Change my mind

Thanks for the responses and ideas as always this forum is super helpful and knowledgeable