1999 Olds Silhouette - Intake Backfire

[steven kiser]

it's obvious there is awy too much fuel getting in. i'm wondering if it starts running well because it goes into limp. maybe we're looking at this from the wrong angle. what would we do if it came into the shop with these symptoms and everyting was original. i think it should be looked at this way before we start looking into possible install malfunctions. have you contacted jasper and opened a warranty claim yet. that's the first thing i do. what's got me here is the popping. under normal conditions a pop through the intake is %80 a lean pop. you sat the cat tube is glowing cherry red and the after a bit everything settels down. it almost sounds like a timed event. the only thing that pops into my mind as a time specific event is evap operations. i remember years ago if a vac line was crossed there was a chance of raw gas being sucked into intake. i'de look at the vac system for the canister. along those lines make sure the fuel regulator diaphram isn't leaking and the pressure is correct. the 02 is reading and hopefully the pcm is trying to make changes but something outside to programmed control is screwing up. i would look at all the grounds for being secured as well as being there. i've seen issues where the ground wire was twisted around a secured harness just to keep it out the way and never connected to the block. i found that one by following the wiring diagram and searching for the ground that was supposed to be there. i would also look for sighns that the harnes has been stretched. even i've left a ground wire attached and only discovered it by seeing the eye and a distorted wire hanging from it. well hope this helps and i'm sure glad it's not in my shop. jobs like these you never get what it's worth.

[Tim Martin]

Steve, yer an interesting fellow tech! Gotta commend ya for that. Yer shop gots to be one fun place to be a part of.

Now then to business: The fuel pressure regulator is not leaking. And if I take the vacuum line off from the engine to the canister purge solenoid, nothing changes. I am about beat, hate to admit it but that's about the long & short of it.

Yeah, this one is not a paying proposition.

[steven kiser]

sometimes the ones that really floor us are the ones that are created by someone while working on it. i've seen plugs in the wrong sensor n occasion. does it maintain fuel pressure with key off". see if there is a crossed injector wire. i know this is almost impossible but i've seen instances where someone has been sucessfull doing the "impossible". this is one that i'de have to come in early to work on before my mind would be clouded by phone calla, customers, exhaust fumes . i'm willing to bet that it's a timed event that is programmed to happen every time the car is started like a evap pump self test. is there a heavy vac pull? hows it run with the oil cap off? is there a high volume of suction going through the oil fill post? egr gasket backwards? intake gasket leaking? what's the air flow reading. if the 02's are reading rich and calling for lean there are very few thigs that can overide or prevent the computer from forcing lean. i've seen cars thinking that they're on pikes peak when they're below sea level or think they're at -45 when it's 90 degrees outside. just for s&g's i'de disconnect a sensr that i knew would throw a code and see if it registers. i've had pcm's flat line before when the battery's been disconnected for a long period before or the key being left on the run position because the vehicle was pushed around the shop. i've seen pcm's trashed because the harness ground wasn't on the block and the plug was plugged into the pcm while the battery was connected and key was on the run position. if you're luck is anything like mine you've probably moved the problem out of your way a 100 times to look at something else. i spent hours one day looking for my brite light flashlight with my brite light flashlite.

[Tim Martin]

Oh yea. Yes sir, steve, I can relate to what you are describing. I have been there done all of the above. But this Olds is very frustrating. I got to keep on this thing till its fixed though. Plan to get on it in a few minutes.

Thanks for your ideas!

[Tim Martin]

where can I locate the sequence of timed events such as evap testing and heated o2 testing when the ignition is turned on with this vehicle? This is info I wish at times to have. Not to find fault with Mitchel's product but there is little in my service info I can find along this line. Perhaps the oem did not make it available to the aftermarket.

[Jeff @ Able Auto]

Tim I believe my Snap-On Solus has the "drive sequence" in the trouble shooter section. It details the process in order to drive the monitors for repair verification. If ya like call me with the vin and I will see if I can get it. I will also check iATN.

[Tim Martin]

thanks for your response but what I am hoping to find out is the timed tests that the PCM does when the ignition is turned on. I had hoped that Theory and Operation would have it but if it is there I missed it. I also have the drive cycle sequence in my MAC Mentor.

[nate23]

If the pop is constant, make sure the exhaust valve is opening. The rocker stud can pull out.

[steven kiser]

hey nate, welcome to the forum and thanks for the tip. it made me think a bit here. i may be wrong and can't look it up at this computer but on a long shot aren't the push rods differant lengths on this engine and if so i wonder if they could be reversed on one of the cylinders. i know that on the engines that they are if they are reversed the intake valve would kiss the piston and not seat after that. if this is the issue here thank nate, he stirred up the dust.