Bucking or jerking of vehicle and Blinking check engine light

[Jeezzuss]

Hello guys,

I have a Saab 9-5 2004 Aero. I already replaced the engine because of my #4 piston blew. It had 76,000 miles on it, I bought with 62,000 miles on it. So now I have a 2008 engine in it, which had 29,000 mi on it, I added 20,000 miles already.  The vehicle seems to buck or jerk when I accelerate under pressure.  It will do so when I am already at high speeds and try to accelerate even more, when I'm going up a hill or incline of sort, and if I have it in semi-manual mode ( leaving it in third gear and accelerating without changing up gears), with the pressure because of not changing gears will cause it to jerk or buck, and the check engine light has blunk when it does so then goes off after a few blinks. Any advice?

Jesus

[Audax]

It's detecting a potentially engine damaging scenario, you *really* need the codes read. My guess would be, wrong/faulty injectors, faulty lambda sensors, bad spark plugs, bad DI cassette or air leak.

[Saabman]

When my DI cassette was failing it showed these symptoms so worth considering 

[stevetreacy]

Hi,
Could be a Cat damaging fault developing. Misfiring that can cause damage to the CAT also makes the CEL blink, Has the CEL stayed on. Will still probably be one of the faults others have mentioned

steve

[Jeezzuss]

Why would it misfire? The check engine light just recently has stayed on gone for a couple of days and back on again , seems to be staying on a bit longer and not going away.

[Audax]

I already explained the causes of why it could be misfiring, it's likely one of those components is faulty or you have an air leak or similar, you need to get the codes read as this will give further information on the cause of the misfires.

If you don't want to get the codes read then you can try replacing all the things I listed above to see if any of them fix the problem but I doubt it would be a very cost effective way of solving the problem.

[TomPaine]

As advised, you need to get it plugged into a Tech II pronto. That's what the CEL is for: instant diagnosis.

[gav]

It's detecting a potentially engine damaging scenario, you *really* need the codes read. My guess would be, wrong/faulty injectors, faulty lambda sensors, bad spark plugs, bad DI cassette or air leak.

or the CPS?

Any OBDII should read the codes too as well as the TECH2.

[Audax]

or the CPS?

I wouldn't think so unless it had been badly installed, CPS doesn't usually give fault codes or problems like detailed above but it is a possibility.

[gav]

The vehicle seems to buck or jerk when I accelerate under pressure.  It will do so when I am already at high speeds and try to accelerate even more, when I'm going up a hill or incline of sort

When mine did this it gave a fault code! There was some serious jerking as if all power was lost for a split second, especially when overtaking. It is a known fault that the CPS do fail.

However, there are lots of options other than this but its worth checking with an OBDII/TECH2 as they will let you know straight away.

[Audax]

When mine did this it gave a fault code! There was some serious jerking as if all power was lost for a split second, especially when overtaking. It is a known fault that the CPS do fail.

However, there are lots of options other than this but its worth checking with an OBDII/TECH2 as they will let you know straight away.

Yours was in the minority though, the CPS usually fails differently to the symptoms given above and I've diagnosed and fitted a fair few myself!

For the original fault given above the CPS would be the last thing I'd replace with guesswork,  but in all honesty if the check engine light is flashing then there will be a code there and it needs reading. Now reading the original post again I wonder if the poster means this fault was always there from installing the new engine? In which case if the engine has been apart then it could be that the timing is out although 20k on a replacement engine with such a fault is a long time!

[Jeezzuss]

The engine light was on and off for few days and then stayed on. So I took the vehicle to the shop. . .  I was hoping it was going to be something related to the issue posted earlier, but I was suspecting it was going to be the oxygen sensor, because I had replaced it in August 2011, and it did the same on and off routine with the CEL back then.  There was an air leak because of a bolt on the turbo that was broken which I believe is where the down pipe comes out from. This caused the oxygen sensor to go bad and it was making a horrible noise because of it. It was fixed , air leak and oxygen sensor replaced. So I thought the problem was solved, and I took it out for a spin and accelerated while the engine was already pressured, it started off okay but then went back to the fault (bucking or shuttering and CEL blinking). It kept shuttering and bucking ,as before, until I took my foot off the accelerator and the CEL did not turn off until the engine settled and then by application of the accelerator. It kept flashing until I accelerated again after the fault had settled and then it went away.  The shop checked for faulty codes but nothing came up because there was no CEL lit and they said they was not much they could do with just an explanation of the problem but no fault code. So what do you guys suggest?

[Steve440]

Mine was like that when the throttle body went, it would be fine for a few days and then be almost undrivable .

Steve

[saabshed]

Buy an ELM 327 code reader that connects to your laptop (less than £20 on ebay) and connect it whilst you drive the car. When the misfire occurs it will (probably) detect it and give you the cause.

I had similar and the code reader detected a pending CPS failure. I'm not suggesting that that is your problem but without a reader you'll just end up replacing expensive bits at random. 

[handjammer]

Hi guys,

I am new to this forum but  I'm experiencing exactly the same problem with the 2004 Aero I purchased 6 months ago. It has 108k on the clock, and has already cost me a bit with a new DIC, ABS ring, cracked exhaust manifold replaced, plus lots of garage time (expense!).

When I got the car and drove it for the first time it was great, although not as fast as I'd hoped. Interestingly, the last in my already long list of engine check lights revealed that I had an air leak, which emanated from the top pipe from the turbo (well done my garage for finding this!), which resulted in the engine being MUCH more responsive and now the turbo easily reaches the end of the red, whereas it never even went into the red before.  The problem I have now is a new one - when nearing the end of the red I have this same jolting effect as described above, in any gear, at any speed. When I let off the throttle the problem goes away, and if I drive the car gently I have no trouble whatsoever.

A search of these, and other Saab forums at the weekend pointed me in several deirections. I'm by no means mechanically orientated, but I'll have a go at certain things, so I replaced all the vacuum hoses with silicon ones. This has made a slight improvement, but I'm no closer to having the acceleration the car is capable of. Next I'll look at the turbo actuator, beyond that it's getting too technical for me.

Technical question - what would I notice as a driver if the engine is misfiring, and is this something I must rectify immediately? I bet it's not cheap either!

I love the car, but I don't think my wife feels the same as I seem to be constantly shelling out on it.

Thanks guys, I appreciate any help you can give me.