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

[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.

[bxd]

OP here.

I think we have the problem fixed.

I did take it to the dealer, and of course they couldn't reproduce the problem. But they did flash the computer with an update under warranty, and said that might help. Well it didn't help.

So then I decided to go ahead and try some "maintenance" and go with the easy stuff first -- cleaning the throttle body. I was surprised at how dirty it was. Carboned up. I sprayed B12 into the TB while my wife kept the engine running, did about 1/2 can and so far after 2 days, it hasn't had one rough start. So I am keeping my fingers crossed.

When I removed the air intake hose (the accordion tube) I did find some oil residue in the hard plastic line that inserts into the top of it. It runs somewhere towards the back of the engine. The 3500 is pretty tight in the RDV, so I can't feel where it goes. What is this hose for? Is it PCV, although I thought the PCV was at the front of the engine.

Thanks.

[TGP37]

PCV is in the front, where air is drawn out of the crankcase. There is a hose that goes to the back to feed air in. The PCV line connects behind the throttle, the fresh air feed connects before the throttle body. This way, at idle conditions, air that is already metered from the MAF sensor is used to draw vapors from the crankcase from blow by. If either hose is disconnected then fresh unmetered air will enter, causing a lean condition.

You MUST have an air tight intake after the MAF sensor.

[bxd]

OK - let's see if I understand what you are saying.

Fresh air is supposed to flow through the air filter, through the accordion, past the MAF, and some of it is supposed to enter that hard plastic hose in the accordion tube, head to the back of the engine and create air pressure that takes some crankcase gases and helps them get sucked back into the engine, but past the throttle body.

Since I found oil in the hard plastic line that should have air flowing AWAY from the intake, the PCV valve might not be working right? And yes fortunately the PCV valve is right in front where its easy to replace. I probably should use some pipe cleaners to try to get as much oil residue out of the lines as possible before dropping in the new PCV valve.

[TGP37]

The PCV is a spring load valve. Under idle conditions there is a vacuum in the plenum behind the throttle blade. This pulls the PCV almost closed for minimal ventilation. When the throttle is opened all the way, the vacuum is gone and the PCV opens up for greater ventilation as blowby can generate pressure if not ventilated.

Under low/no load, the one plastic tube feeds fresh, filtered, measured (MAF) air to the crankcase in the back side. But it is a passive air feed, it doesn't provide any positive pressures. It is the vacuum present at the PCV valve that draws upon the fresh air feed, through the crankcase.


Shake the PCV valve, if it doesn't rattle replace it. Also check the hoses and grommets to make sure you have an air tight seal. You do not want any air leaks past the MAF sensor. Or the filter but that is another issue.