matmanx1

Over the last week my GX has developed a strange issue. It sometimes takes 3 or 4 tries of turning the key before the engine fires up. It turns over strongly and quickly but it isn't "catching". The weird thing is, it doesn't happen every time. Here is what I have noticed:

1) Leave the vehicle parked overnight - no issues starting. It starts right up.

2) Crank the vehicle after having only been off a few minutes (like after you run in to pick something up at the grocery store) it cranks right up.

3) Let the vehicle sit for between 1 and 4 or 5 hours and the problem appears. It turns over and over and over but won't actually start. Anywhere between the 3rd and 5th turn of the key it will finally catch and actually crank.

In all cases, once it cranks it runs smoothly and normally with no issues.

I have replaced the battery thinking that was the issue but that did not fix the problem. Also strange is the fact that this problem occurred after I replaced both front door speakers, an operation that required me to have one or more doors open for an hour or so at a time (hence why I thought it might be a weak battery).

Any help on narrowing this down would be appreciated.

chiph9

How long has it been since you changed sparkplugs? Changed the engine air filter? Are you holding the key or letting the computer start it? (you can turn and release, and the computer takes over)

If all those are good, I would look at fuel pressure & quality.

Chip H.

IanB2

Strange that it isn't a hot or a cold start issue, but rather a "warm" or long enough to cool down starting issue.

Makes me wonder if it's an immobilizer chip in the key issue or something weird like that?

180ls1

Try a tundra forum. There will be a lot more 4.7 knowledge out there besides here.

Answer me this, does the cranking speed change at all from hot - cold - warm?

My initial guess would be the crank position sensor, but that is a somewhat wild guess given what we know.

chiph9

This was the term I was trying to think of:

https://en.wikipedia.org/wiki/Vapor_lock

Haven't seen it in years (since my last carbureted car in the late 80's), but it matches the description perfectly.

Get your fuel pressure checked at the rails.

Chip H.

co4wheel

But a F.I. car is not a closed system like the old carborator days. F.I. has a effective return line from the manifold.

I would check fuel filter, air filter, spark plugs and fuel pressure. Any maintenance item left undone should be performed.

chiph9

If the fuel pump in the tank is weak, you would get the same effect.

Agree on fuel filter. A clog would also result in low pressure.

Chip H.

matmanx1

Thanks everyone for the suggestions. It has been a crazy week and I have not been on the forums much. My GX is a 3rd car and I don't drive it every day and as long as I just crank it in the morning, go to work and then crank it in the afternoon when I am ready to leave, the problem never manifests itself.

To answer a couple of questions: The crank speed of the engine never changes. It turns over quickly every time, regardless of whether or not it actually cranks.

The 120,000 mile service is coming up. I believe that is the one with the spark plug change. I am at 118,500 (approximately) right now.

I did think about fuel pump and crank position sensor but will need someone with some proper diagnostic tools to really dig in to the problem.

My wife and I are planning on using the GX to go on vacation in June so sometime in May I will have this problem properly diagnosed and hopefully fixed. At that point I will report back. I do appreciate the suggestions and responses!

IanB2

For clarity sake, cranking is the engine turning over with the starter, firing would be if it starts. The engine could crank over, but not fire/start, for example. To say it turns over but doesn't crank is confusing language.

At nearly 120,000 miles, your due for a set of spark plugs, and a fuel filter if both are original. Get those changed and see if you still have a starting issue. That's where I'd start.

allwheels

Although its never a bad idea to do spark plugs during the normal maint. interval, it won't solve your problem. I guarantee it. I'd lean more towards the fuel pump or fuel system.

FrankT

A dirty MAF sensor will cause similar issues; If it does not detect air flow the fuel pump will not come on.
I would clean the MAF sensor.

good luck

BlackCat81

That's not correct. The fuel pump primes before the truck even starts. Also, the truck will run (badly) with the MAF sensor disconnected.

180ls1

This, except i am betting its not fuel related. You can rent a fuel PSI gauge at the local auto store and check pressure. Its simple to do.

matmanx1

Problem diagnosed! And it is indeed a key issue. On a whim I decided to try the valet key (the one without the fob) and it works flawlessly every time. Only the main key with the lock/unlock buttons causes the problem.

When I bought the truck from a forum member here the main key was not in use due to the original housing having come apart. I bought a new housing and blade from 1010keys on Ebay and switched the "guts" into the new casing and thinking back, that is exactly when the problem started.

I guess there's something wrong with the original key for it to be intermittent like that. Thankfully I can keep the fob with the buttons on my keychain for locking/unlocking and just run with the valet key for cranking the truck.

Thanks to all for your suggestions but if you ever run into this type of behavior, check your key!

IanB2

Glad to hear you got it sorted! Check with your local dealer, see if they can reprogram the chip or something to salvage the main key.