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QUOTE: "All posts on the web pointed to the Opti."

NOPE. Not on this forum it woont have. With just your second two prior sentences I immediately thought FP. Now that you've joined up it might save you some $$$. Like it has the rest of us. lol
 

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Sorry, didn't read all 13 pages so this may have been mentioned but I have personally worked on two B bodies where the cause of misfires was from a bad injector pigtail which I diagnosed with a simple noid light. One car had an intermittent misfire that would be very obvious when it was acting up. On the other car, it wasn't as noticeable (just like pulling plug, some will have more of effect). If you're getting a strong misfire, put your fingers on each injector and you could feel if it is functioning or not. The noid light will let you know if it is the harness and not just bad windings in the injector. Don't forget to wiggle the harness around while testing it. On both cars I had the problem with, the loose connection was at the pigtail itself and was easily fixed by soldering in a new pigtail.
 

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Also,as far as the web is concerned, all problems always lead to the opti LOL. I can't say I wasn't victim of this myself. I swapped two optisparks once figuring out why my car was misfiring under load so bad it would barely move after a race. Ended up finding 3 bent up pushrods under the valve covers when the optisparks didn't fix the issue haha
 

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Sorry, didn't read all 13 pages so this may have been mentioned but I have personally worked on two B bodies where the cause of misfires was from a bad injector pigtail which I diagnosed with a simple noid light. One car had an intermittent misfire that would be very obvious when it was acting up. On the other car, it wasn't as noticeable (just like pulling plug, some will have more of effect). If you're getting a strong misfire, put your fingers on each injector and you could feel if it is functioning or not. The noid light will let you know if it is the harness and not just bad windings in the injector. Don't forget to wiggle the harness around while testing it. On both cars I had the problem with, the loose connection was at the pigtail itself and was easily fixed by soldering in a new pigtail.

When doing my intake gasket R&R I found that the 5/7 injector pigtail had worn through to the copper from just rubbing up against other wires in the harness. That area is where all the wires for the engine harness bundle together in to the main loom.But yeah.../I just discovered it by chance. It could have easily progressed until it started arcing or something.
 

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Couple years ago I wrote this down in my maintenance log, had an intermittent issue that put me into limp mode and kept me down for weeks.


"Comprehensive Research performed. Solenoids in Trans targeted first due to Impala SS Forum research. EFI Fuse (#4) repeatably blowing, shutting down everything associated with that circuit. First out DTC is reliably #83, TCC Circuit Failure followed on the very next data resolution point, TDC #48 MAF Sensor Fault. Next out is #84, 3-2 downshift fault. SS only has 3rd gear for forward motion, reverse also works. From the three GM service manuals, pieced together that loss of power to the 1-2 and 2-3 can put the trans in one gear and keep it there and also the 3-2 downshift controller will cause a soft landing into 3rd gear and keep it there. DTC 26, 27, 29 also appear after awhile, which makes sense cause they all route through the #4 (EFI) Fuse.
Tested new solenoids for appropriate resistance, SAT, removed old and tested, SAT for resistance values however the 367B did not cycle when mechanically agitated. The 394 (3-2 control sol) was not pushed in all the way, which was weird but I'm undecided if it was making a difference. Check engine light still on, reflashed PCM with a delete of the Air Pump DTC check and set the Air Pump Enable to 154 Deg C minimum. Ran diagnostics again (in garage 2, 2/3/2018). SAT

(24 hours later)Failed again, moved on to the rest of the circuit. Since the O2 Sensors have been replaced recently, took a look at the canister purge valve. Unplugged it and tested it for several days. Failure did not repeat. Reflashed computer with cansiter purge deleted. Running satisfactory at this time."

Its been running SAT ever since. That canister purge valve was the true root of the problem.
 

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Just spent a good chunk at the mechanic getting a new crankshaft seal, oil pan gasket set, gasket kit & oil adapter. Lots of labor involved with removing tranny, removing driveline, removing flywheel, unbolting engine mounts from cradle, etc. .

Now my engine is misfiring. Valve #4 is "tight". New spark plug didn't fix the issue. They told me to drive it a bit and see if it loosens up. If I need to take it back, They're estimating $600 in repairs.

The engine was fine before I took it in for the oil leak. This engine trouble is an unfortunate coincidence. I should add that I drove the car today and the engine light remains on. The engine seemed fine except a few times when I stopped completely at a stop sign. One time the RPM dropped really low, and there is a rough idle at times. Apparently the issue comes and goes, as per my mechanic. When I picked up the car yesterday it was shaking as it idled. Today it was a bit rough, but not too bad. ...and drove pretty well.

Any thoughts as to what might be the issue/cause?
 

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Just spent a good chunk at the mechanic getting a new crankshaft seal, oil pan gasket set, gasket kit & oil adapter. Lots of labor involved with removing tranny, removing driveline, removing flywheel, unbolting engine mounts from cradle, etc. .

Now my engine is misfiring. Valve #4 is "tight". New spark plug didn't fix the issue. They told me to drive it a bit and see if it loosens up. If I need to take it back, They're estimating $600 in repairs.

The engine was fine before I took it in for the oil leak. This engine trouble is an unfortunate coincidence. I should add that I drove the car today and the engine light remains on. The engine seemed fine except a few times when I stopped completely at a stop sign. One time the RPM dropped really low, and there is a rough idle at times. Apparently the issue comes and goes, as per my mechanic. When I picked up the car yesterday it was shaking as it idled. Today it was a bit rough, but not too bad. ...and drove pretty well.

Any thoughts as to what might be the issue/cause?
They may have damaged the optispark when they went in and replaced your seals, some mechanics don't take responsibility for those types of things from time to time. What code is it throwing?

Make sure the plugs "clicks" twice when plugging them into the Opti.
 

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They may have damaged the optispark when they went in and replaced your seals, some mechanics don't take responsibility for those types of things from time to time. What code is it throwing?

Make sure the plugs "clicks" twice when plugging them into the Opti.
Thank you for the reply. I think my mechanic might be hip to the optispark potential, as I do recall him saying that if the problem doesn't fix itself the repair will involve the removal of the water pump. Let's assume it's the opti. What are the chances that the issue presented itself out of sheer coincidence, and not as a by-product of last week's repairs?
 

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Its possible! Whats the mileage/age on the opti? Is it the original opti?? Mine is pushing 86k miles and not showing any signs failure yet (knock on wood) but i’m sure it will need to be replaced soon, gm rated them to last up to 100k miles all depending on the lifestyle of the car through the years of course.
 

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Hey guys. Had a horrible misfire and hesitation at part throttle, would absolutely fall on its face when you hit the pedal, except at WOT. Running over all the old hoses with propane did not reveal any intake leaks. Amazingly, even though the opti was getting poured on, a new wpump and opti didn't solve it! I noticed it only misfired when it was moist or humid out... Changed the plug wires cause some of them were burnt and arcing (hooker headers lol), still misfiring!

Turns out the drivers-side engine ground at the back of the head had come loose, and as well the passenger side ground at the front of the head was connected to the BLOCK, not to the head! Looks like i was in a rush when putting in the fresh LT1, live and learn! :rolleyes:
 

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Well, that certainly seems above and beyond the call.- Thanks for dropping in and volunteering your problem & fix.
 

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Its possible! Whats the mileage/age on the opti? Is it the original opti?? Mine is pushing 86k miles and not showing any signs failure yet (knock on wood) but i’m sure it will need to be replaced soon, gm rated them to last up to 100k miles all depending on the lifestyle of the car through the years of course.
My 96 is just like yours. Just above 85k miles with the original opti. I just got word from the mechanic that the code was P0304.

I've driven the car a couple of times and the problem has continued to come and go. The last time I drove it, the engine light never came on, and the idle was only slightly "off" but not too bad. I'll drive it again soon and see how it goes.
 

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Hi, P0304 is pretty specific. 300 is random misfire. you got a 304 so cylinder #4 is misfiring.
If visual inspection shows opti ok and it passes the paper suction test off the blue nipple going into the stock elbow, i would trace backwards, #4 plug,wire,fuel injector, injector wiring, etc.....

Good Luck.
-ALF out...
 

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Hi, P0304 is pretty specific. 300 is random misfire. you got a 304 so cylinder #4 is misfiring.
If visual inspection shows opti ok and it passes the paper suction test off the blue nipple going into the stock elbow, i would trace backwards, #4 plug,wire,fuel injector, injector wiring, etc.....

Good Luck.
-ALF out...
Thank you very much for the info. I'll be laying low for a bit, but when I have news I'll follow up here. Thank you again.
 

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Actually, there's one more thing I'd like to mention. Note that I have not yet taken the car to the mechanic since the P0304 code. The car starts fine, and now the engine light has stopped coming on. Yet a slight problem persists: most notably, if I come to a complete stop at a stop sign, the idle dips way low, and it feels like the car is about to shut off. But then in comes back to equilibrium after about 2 seconds. And the idle is pretty ok after that. ...not a 10, but I'd give it an 8 or so out of 10. And, another thing. When I get out of the car after I get home, it smells like gas fumes.

There are occasions when I'll step on the throttle and the engine doesn't respond as I'd expect. It feels a little weak. That's mostly before the car has warmed up. And when the car has warmed up, the thermo reading doesn't quite get to that bold notch that is about the half-way point. You know that notch? Well, there's a notch below that, and the needle stops before it gets to that notch. So it's not running hot, so I presume it's not the opti(?).

Any thoughts are welcome.
 

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Actually, there's one more thing I'd like to mention. Note that I have not yet taken the car to the mechanic since the P0304 code. The car starts fine, and now the engine light has stopped coming on. Yet a slight problem persists: most notably, if I come to a complete stop at a stop sign, the idle dips way low, and it feels like the car is about to shut off. But then in comes back to equilibrium after about 2 seconds. And the idle is pretty ok after that. ...not a 10, but I'd give it an 8 or so out of 10. And, another thing. When I get out of the car after I get home, it smells like gas fumes.

There are occasions when I'll step on the throttle and the engine doesn't respond as I'd expect. It feels a little weak. That's mostly before the car has warmed up. And when the car has warmed up, the thermo reading doesn't quite get to that bold notch that is about the half-way point. You know that notch? Well, there's a notch below that, and the needle stops before it gets to that notch. So it's not running hot, so I presume it's not the opti(?).

Any thoughts are welcome.
I'm chasing some issues to and ran across a post about fuel pressure regulator could cause the gas smell and also could cause idle issues. What I'm chasing is after about 45 minutes of idling, the engine starts to run rough, enough to throw a P0303 (Cylinder 3 Misfire). I've replaced the coil, ICM, and MAP as all were original on a 185K mile car. Plugs and wires are new, not sure of the opti. That being said, I was told by a mechanic to watch the short term fuel trim and that would be an indication as to what is going on. Sure enough, Bank 1 STFT shot up to 46% while Bank 2 stays around 2%. This apparently means I have a fuel issue on Bank 1 where it is requesting more fuel but not getting it. I have a call out to my mechanic friend to see if I'm correct and could possibly be the Fuel Pressure Regulator. That being said, you just may have a fuel issue.
UPDATE Ran the car more and it started running the numbers up on Bank 2 for STFT and now I'm getting a P0300. Car will run but when it starts missing, it gets really bad, to the point it will die and you almost cannot start it again. If it does start, it almost immediately dies again. I'm now looking to replace the fuel filter and fuel pump.
Update 2
Bought a fuel pressure tester and found out I'm only getting 25 - 28 PSI to the rail and that is not at KOEO. I get nothing at KOEO. So fuel pump and filter it is. I'll update as soon as it's changed.
 

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Actually, there's one more thing I'd like to mention. Note that I have not yet taken the car to the mechanic since the P0304 code. The car starts fine, and now the engine light has stopped coming on. Yet a slight problem persists: most notably, if I come to a complete stop at a stop sign, the idle dips way low, and it feels like the car is about to shut off. But then in comes back to equilibrium after about 2 seconds. And the idle is pretty ok after that. ...not a 10, but I'd give it an 8 or so out of 10. And, another thing. When I get out of the car after I get home, it smells like gas fumes.

There are occasions when I'll step on the throttle and the engine doesn't respond as I'd expect. It feels a little weak. That's mostly before the car has warmed up. And when the car has warmed up, the thermo reading doesn't quite get to that bold notch that is about the half-way point. You know that notch? Well, there's a notch below that, and the needle stops before it gets to that notch. So it's not running hot, so I presume it's not the opti(?).

Any thoughts are welcome.
yep, sounds like a misfire. when i had a broken #8 plug i had similar symptoms as you. did some data logging to find that that banks O2 was reading way low, and so the STFT was reading way high. so it was spitting more fuel and not burning it on one of the cylinders, the thing stank of gas!
 
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