Hoping someone here may have more ideas than my local dealership in solving a problem.

I have a 2007 4.3 with 28,000km on the clock, which started playing up about 6 months ago. On the first start of the day, it fires promptly but barely runs - idling well below 1000 RPM and chugging away like it's running on 3 cylinders for 10-15 seconds, at which point idle speed suddenly increases and it runs smoothly. Driving away, performance is smooth but sluggish for the next minute or so. After that, everything settles down and it performs normally for the rest of the day. Restarts at any time are the typical Aston 'explosive' events, and performance is smooth and faultless.

Its just those cold starts that are the problem. Quite embarrassing to have an Aston chugging away like a clapped-out Cortina..

Last time I had it in for service, the dealership assured me everything was in order, and it was just a fuel issue, due to changing fuel mixes for summer/winter seasons. The next refill would solve the problem, so they said. Suffice to say, after many refills, the problem remains.

If I didn't know better, I'd say that an automatic choke function wasn't operating - the symptoms are exactly what I recall from the bad old days when forgetting the manual choke on a cold start. Being injected, maybe the issue with my V8V is a bad temperature sensor, or injector problem, or…?

Any ideas gratefully accepted.

 

Hi Keith, have you figured this out yet? Our cars are VERY sensitive to what gas/petrol we use. I notice a huge difference in drivability going from one fuel source to another. Try using a different fuel station (different brand/company) and see if it gets any better.

 

I'm not sure if your problem is fuel related or not. That being said my AMV8 is also very sensitive to fuel. I have actually found that My car runs best on Chevron 91 octane.

I have had issues with Shell, Sinclair, & a Phillips 66 (back when I was transporting the car from Texas to home when I bought it). Issues being mostly the emission system warning light. I have not had issues like described in your cold start description.

 

What have you done on the car so far, has the dealer replaced anything yet? Is there a in-depth story the tech might of wrote on the work order..just trying to get as much info I can

 

Thanks for your responses.

No progress or solution has been found as yet, and the dealer did no work towards resolving the issue. The dealer response to the work order was simply to say that it was a change of season fuel issue, which would resolve itself. Which of course it hasn't.

I know the fuel here (Sydney) does vary a lot - my other car is a Mazda RX-8, and it's extremely sensitive to fuel. On decent fuel it runs sweetly, but get a bad batch and it becomes diabolical. Imagine a rotary with even less(!) torque, that no longer wants to rev(!), and showing signs of preignition. Driving becomes a miserable experience. So I'm acutely aware of where I get fuel. I only ever use 98 octane, and for the Mazda at least, have found BP to be the only reliable source. Shell is sometimes OK, sometimes not. All others not worth bothering with. I've only ever put BP 98 octane in the V8V, and given my experience with the RX-8, have been hesitant to try anything else.

I was talking with an old-school mechanic last week, and based on my description of the symptoms, his diagnosis was also an automatic choke function being inoperable. His suggestion was either a faulty temperature sensor (i.e. the computer doesn't know its a cold start), or a fuel pressure regulator issue. He wasn't familiar with Astons to know how they tackle fuel pressure regulation, but offered some general suggestions on how its normally tackled.

Next step might be to get the dealer to test those items.

Keith

 

There is a engine coolant temp sensor and a ambient temp sensor. These are the "choke" sensors for temp. The coolant temp gives the engine temp reading to the PCM and also sends a feed to the gauages via a CAN-Network(through 2 wires twisted as a binary code).

The ambient temp alos dives a reading of the exterior air temp in front of the grill which is where the intake inlets are. It is not a temp sensor for the air passing the MAF sensor but rather just an indication of the exterior temp the car is travelling through.

If the coolant temp sensor was bad and showing too hot(aka not a cold start), then the gauge in your dash will indicate this also by showing the temp in teh medium area and not at Cold. If the ambient was bad, your temp display in the radio would be more than +/- 5C out of spec when compared to the temp in front of the vehicle near the grill.


Forget the mileage on the car. I think what you need is to start with basics. Check the air filter for cloggs, check the spark plugs and verify gap, check the "battery" (even though it starts it might be low in volts causing the PCM to dip below 9V, which will then need it to wake up fast and adjust). When the car starts it is in a "open loop" which means its not really at any sensors for input, the PCM will run on a preset map till "closed loop" is achieved, then the PCM will look at things like O2's to help dial in the fuel trim and performance.

I would also do afuel pressure test and injector leak test. You might have little fuel pressure on start up, or a possible leaking injector which is fouling the plug on start-up, after a few revolutions the plugs drys and fires up to complete the combustion.

I would also scan for a fault code, just because there is no engine light on there could be a DTC stored that isn't emisions related, which might help further with the diagnostics. i would also check and make sure the misfire factors are stored. If the misfire factors are not stored, you will not store any faults for a misfire, even a misfire on start will not be stored. Which could be one of your issues, even it's missing on start-up you should get a DTC and engine light if it's bad like you desbribe. Once they are stored, you can then run a misfire count and see if there are other cylinder missing while running while cold/warm/hot.

So who can do all this..well the misfire factors are dealer only, the rest any one can do that has a injector leak tester, fuel pressure gauge with fitting(or use a scanner), battery tester with load test(some parts stored rent out tools). Once all this is done, you will then have a road to follow further in diagnosing...this isn't really complicated for the average mechanic, it's just doing your basics to see which directions needs to be taken

 

Just a quick note to say that I haven't had this problem (don't even have a V8) but *dang* Irish07 . . . what an amazing write up and diagnostic. I'm totally mechanically inept but I'm learning so much just reading your comments. So much great info on this forum and just wanted to say a public "thank you" for your contributions.

 

++1, It's so great to have such a knowledgeable Technician blogging on this site to help us all to better understand our Astons--THANKS IRISH07!

 

Irish, is this the external air temp sensor? Mine has... gravel... in it.

 

No that looks like the air box drain pipe. It is near the lower grill.

 

This is dead center, behind the lower grill, behind the oil cooler. I think that's the oil cooler. I don't have my car in my living room for reference

 

Looks like the drain for the air intake tube, which are dead center. Looks more like this...

 

Ah, okay. I guess I wasn't expecting the drain to be in that spot!

 

Irish, thanks so much for your detailed input.

I had hoped the issue may have been something simple like a temperature sensor, but based on your post, thats not the case. On a cold start, the engine temperature gauge is fully bottomed out, and the ambient temperature reading on the radio is within 1 deg of measured temperature at the front of the car. Oh well..

Your suggestions will give me the basis of a work order for the dealer now. I used the dealer years ago for a Porsche 928GT, and found their 'technicians' to be extremely competent in driving the diagnostic machine. So if a fault could be diagnosed by the machine, they were onto it. If not, they were completely clueless. So hopefully a detailed work order might give them a starting point that the diagnostic machine didn't.

By the way, does the V8V use a separate injector for the choke function, or simply increase the duty cycle of the normal injectors?

Thanks again,
Keith

 

Hey Keith,
This might not be your problem but I think it actually helped smooth out my engine on cold starts: I had a fault code for my MAF sensor, so I replaced it. My car ran much more smoothly this morning than it usually does. I'd imagine if this was the case for you, you'd have a fault code as well. Might be worth keeping in mind while you're troubleshooting. Here's the old MAF (dirty, left) and new one (clean, right)