3500 hard start

[bxd]

Hello.

2007 Buick Rendezvous 3.5L, bought brand new May 2007.

I would say the car wasn't even one year old before the first failure to start happened. But it was very rare, so we ignored it, and it has progressively gotten worse. About 70,000 miles now.

You turn the key, the engine cranks, but it seems like the starter disengages just a little too early. Sometimes the engine doesn't start at all, sometimes it seems like it has just BARELY fired and dies with some chugs. It used to be that the second time you tried, it would always start. Still usually true, but now sometimes it takes even a 3rd or 4th try.

I have kept up with air filter, oil changes. Once it starts, it idles very smoothe and power is as good as ever. Never 'coughs' at a red light or anything.

Still under GMPP extended warranty. Took it to dealer over summer, they said they couldn't reproduce. Someone said there is a 'hard start' TSB but dealer denies.

Ideas??

Thanks
Brian

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[Joseph Upson]

Hello.

2007 Buick Rendezvous 3.5L, bought brand new May 2007.

I would say the car wasn't even one year old before the first failure to start happened. But it was very rare, so we ignored it, and it has progressively gotten worse. About 70,000 miles now.

You turn the key, the engine cranks, but it seems like the starter disengages just a little too early. Sometimes the engine doesn't start at all, sometimes it seems like it has just BARELY fired and dies with some chugs. It used to be that the second time you tried, it would always start. Still usually true, but now sometimes it takes even a 3rd or 4th try.

I have kept up with air filter, oil changes. Once it starts, it idles very smoothe and power is as good as ever. Never 'coughs' at a red light or anything.

Still under GMPP extended warranty. Took it to dealer over summer, they said they couldn't reproduce. Someone said there is a 'hard start' TSB but dealer denies.

Ideas??

Thanks
Brian

Keep it simple, spark plugs, fuel filter if it has one, run some fuel injector cleaner through the tank and make sure you have a good battery, otherwise the colder the temps get the lower the cranking amps available for starting.

[bxd]

No fuel filter on this vehicle.

Have tried numerous cleaners including Techron Concentrate.

Air filter done.

Battery cranks engine fast... car starts strong in freezing cold or 90* heat vast majority of time.

I suppose it could be spark plugs, but the idle quality is excellent, power is fully there, and when it doesn't start, you try again and it starts perfectly, if there was a physical problem with a plug I'd suspect lumpy idle, misfire, hard start all the time.

[carbon]

Our '06 Saturn Relay's 3500 will do the same thing once in a while... it's at 104K miles and I am thinking it needs a few things. Like plugs, perhaps wires, probably an O2(not that it would affect starting)...

Not that it is the cause of the current problem, but all cars have fuel filters, even if it is in the tank, which is most likely is with the 3500's returnless fuel system.

[bxd]

Thanks, you are right. I'm sure it has a sock-style mesh filter in the tank around the fuel pump intake. But there is no filter on the fuel lines underneath the car like you'd find under a 1990's GM V6.

Spark plugs are rated to 100,000. They're hard to do on a Rendezvous, and the last time I pulled long life plugs at like 60,000 miles (different car) they were still in great shape and it was a waste of time and money.

I could try an upper intake cleaning with some SeaFoam before my next oil change. Is there a preferred vacuum hose to use for that or just pick any?

Thanks.

[TGP37]

Coolant leak into combustion chamber or fuel injector leaking. That's my guess.

Fluid builds up when shut down making the next start hard until all the fluid is burned off and/or ejected in exhaust.

Plugs may indicate the offending cylinder.

Check for hydrocarbons in the coolant. Cheap kits available at many auto stores. A leaky injector can be heard at the throttle body with the fuel system primed.


edit: A dying fuel pump can, in some cases, act up like this too. Listen carefully by the tank while a friend primes the fuel system (key on engine off). Anything but a clean hum is suspect. Check fuel pressure as well during the hard start condition.

btw, ruling out spark plugs w/o checking them is a bad idea. You can end up spending far too much tossing parts at it that aren't bad. Like Joseph said, keep it simple. (Air - Fuel - Spark - Compression)

[bxd]

Thanks guys. I will take it back to the dealer and tell them it's getting worse and make them run the diagnosis. Especially since it's still under GMPP. Used to love working on cars (still do) but time is at a premium nowadays.

[carbon]

I love cars too... but I get epically tired of working on the daily drivers.

I could futz around with the Fiero all day...

[pokepoke]

I have the same car (2007 120k miles) and am having the same problems. I have an alldatadiy subscription for the car and there is no TSB for this. We bought this car used two years ago and it would be hard to start every now and then, but now it's every time. To start the car, we have to press the accelerator half way down and it will start fine. The strange thing to me is that if I hold the accelerator at that position while starting the car and through it starting, the engine doesn't rev up. If I back off and push back down the engine will rev. I used my father's Nemisys to watch throttle position while testing all of this and it seems to have a command throttle of 22% with key on, but not running, but once you turn the engine over it drops to 7%. It will begin to start then cough and die. I'm really not sure how to troubleshoot this further. Any ideas?

[TGP37]

Hard to know what is going on but the Throttle Position reading should not change if the pedal isn't moved. If it is changing, check the wires running to it. Or replace the TPS.

A failing tps can cause funky symptoms.

It may be something else, like a bad battery connection starving the system of proper voltage under heavy load. Starting, night driving w/ heater, etc. As a result, other sensors that rely on that voltage may act goofy.