running rough!!

[prophiseer]

a compression test won't exactly tell you valve guide wear . . . but it'll tell you if the piston rings are starting to fail, or if you have a burnt valve, valve seat, or possible major damage to the heads. Even more of a probability if the only DTC that's getting thrown is a P0300. There's something causing the PCM to flag a misfire, but the PCM doesn't see anything wrong with any of the input/output controls to flag a specific cylinder.

I just had a 2000 Cadillac Escalade with the vortec 350 that was throwing a P0300 - #6 cylinder was only pumping to 60psi on a compression test . . . loosened both rockers (to close the valves), and put shop air pressure on the cylinder, and she was blowing out the intake . . . yanked the heads off, and it turned out to have a torched valve seat.

[Rootie524]

and the mystery continues!!

got a new MAF sensor..guess what?! that wasn't the problem. so then im like..ok..compression test. did it. and it seemed pretty consisten across the board. only i did notice a spike in compression on cyl 4. all of them seemed to be 160psi..but cyl 4 i got 180psi. also, when i removed the spark plugs there seemed to be oil on them. not at the electrode part but on the threads and stuff. idk if that means anything.

also, i started to notice everytime i would stop cranking the engine and went to look at the compression gauge, it would start to go down. now idk if thats supposed to happen or if i just got a bad gauge (bought from harbor freight), or if thats a sign of a blown head gasket or valve that arent seating properly. but it seemed to go down faster in the front than in the back.

when i had the heads removed before, i didnt get them milled or anything because they seemed fine. plus i knew i would be rebuilding the engine soon anyway so i just said the heck with it. so it's possible i have a smalllll head gasket leak but i wouldnt think it'd cause alllll of this.

in addition, if i had a head gasket leak wouldn't it cause problems all the time and not be off and on? thats why i ruled that out as a possibilty. but like i said..it seems to be running poorly all the time now. it used to be bad for a minute than good again but now it seems to be bad all the time and good very rarely..so what ever it is is getting worse.

so from all that info..any new guesses? it's either really serious or really simple. spun rod bearing? piston rings? needs a new black ice air freshener?

here's a video of what i was talking about on the compression test: http://www.youtube.com/watch?v=vBwIQLC2KNs

[robertisaar]

being that it was intermittent before and slowly progressed doesn't sounds like a mechanical issue, it sounds like a sensor/module failing

[Rootie524]

yeah that's what i thought at first..but it's possible sometimes valves dont sit right..or a rod bearing spun and sometimes was in the right place (idk much about spinning a rod bearing as u can tell), or fuel injectors or something.

and if it were a sensor wouldn't the PCM throw a code for it. i checked all the obvious sensors and im still looking but i really have no idea.

[Rootie524]

just was fooling around with things and i decided to pull an ignition wire from the 4th cyl. it didnt change how the car ran..but it was giving spark. then im like ok..so i put it back and removed the ignition wire from the 2nd cylinder..and it sorta changed how the car ran. i would think if you were to start removing ignition wires it would cause serious running issues with the car..but it really didnt.

so that could be a good sign that my fuel injectors are fucked...or that im not getting the right amount of spark. is there a way to test spark voltage. something is up here and im going to get to the bottom of it god damnit!

[bszopi]

That right there sounds like the coil pack serving cyl 4 (and 1?) is starting to go bad. Try pulling all wires and see if only 1/4 (or whatever the pair is) do NOT cause a change to how the car runs. Then, switch 2 coil packs around and see if the condition follows the coil packs. If it does, replace the coil pack.

[86FieroSEv6]

If you are pulling the wire from the coil, a good coil will easily cross a one inch gap and after you pull the wire back farther it oughta leap to the bracket or hold down screws of the coils. As stated above, confirm by pulling the companion wire. If you have hot spark from both towers on that coil, you can rule out the crank sensor, ICM and coil. What remains is the spark plug wires, spark plugs or lack of fuel or too much air (vacuum leak). Your gauge slowly bleeding off pressure is due to contamination from the cylinder getting caught in the valve core at the end of the gauge hose. If you want the true health of the cylinder, you use a leak-down gauge set, but an air compressor is required to use it.

[Rootie524]

so the gauge dying down has nothing to do with blown head gaskets or valve not seating?

and i know it seems like the coil is bad but i replaced the damn thing already with the ICM and it did the same thing it did before. unless something caused it to go bad again.

just a quick recap for those wanting the facts quick:
replaced coil pack and ICM - Problem Remained
replaced spark plugs (properly gaped) - Problem Remained
replaced ignition wires - Problem Remained
replaced MAF sensor - Problem Remained
did a compression test: read 160psi across the board except for cyl 4 which seemed to be around 180psi
removed both valve covers and ran car..valves moved up and down as they should
checked for clogged air filter by removing and running car - Problem Remained
temporarily replaced PCM - Problem Remained
checked the obvious fuses, sensors, wires, etc - Problem Remained

then today i randomly pulled cyl 4 ignition wire and the car did not run differently and the end of the ignition wire when placed up against the metal frame of the car produced a spark. then removed cyl 1 ignition wire and the car sort of ran differently and that one produced a spark as well.

Im definitely getting spark..but i was just wondering if its getting enough..i was just wondering if there was like a spark voltage tester or something. Ill do the coil test as previously mentioned though. But from all this im thinking it might be one or more of my fuel injectors.

ALSO: when i did my cam shaft i replaced the crank shaft position sensor (w/ wire leads) because it got damaged. are there two crank sensors. the one with leads and the one without..or does it depend what year car i have and only have one? because if it has two..maybe the one i didnt replace is damaged. And is it possible my cam shaft position sensor is dying? it's a possibility but i would think if it were a sensor the computer would tell me that.

[Azrael]

A good compression gauge should hold the pressure reading until you press the release button. If there's nothing causing it's valve core to stick open then you might need to take it apart and reassemble the fittings with teflon tape. 160 psi isn't bad if the motor is in the 150,000+ mile range. At ~120,000 miles my 3100 was between 170-185 psi. Strangely, the hottest running cylinders (5 and 6) had the highest readings.

The crank sensor on the firewall-side of the engine is the 3x and has no wires. This one is critical to keeping the engine running. Either it'll cause you car not to start or stall randomly or whenever it gets hot enough. The crank sensor behind the dampener is the 24x and can cause a rough idle and or poor starting if it fails. I started a thread asking about diagnosing this sensor recently.

You can check if the injector for that cylinder is sticking by lightly tapping it with a ratchet extension and hammer. There's a video on youtube demonstrating it.

[Rootie524]

oh ok..so if the 3x sensor went i wouldn't really even be able to do much. and the 24x sensor is new so that's all good.

well..im confused as shit right now. i just went outside to screw around more with pulling plugs while it's running and whatnot. i pulled the 4th cyl plug while it was running and it didnt do anything. i turned off the car and pulled the 4th cyl plug so it would already be removed for the car start..the car started but ran even more rough. WTF?! i pulled two random plug wires and car struggled and would not start. also when i pulled the 4th plug prestart and then started it u could really smell gas out the tailpipe so im guessing its getting fuel properly in that cylinder at least.

so long story short i was fucking around with the plugs..pulling some..starting and stopping the car..doing some tests..and what do you know..the car is running fine now..i runs but still has a slight backfire and for about 2 seconds reverted back to its stumble/growl/rough running then was fine. this is what it does..runs poorly, then runs decent. only this time i did something to cause it to run decent.

also..i pulled the line going into the top of the FPR and for a second i swear the car revved better..but im not totally sure.

so wtf does this mean? im getting a heck of a lot of spark. it's like a lighting show. some seemed stronger than other though but i cant be sure unless i test the voltage. and i just replaced the damn coil pack so something has to be causing it to go to shit.

again i ask..how stable are these cars for ignition advance tuning. because like i said i have ignition timing in it..but it ran without a problem for like a month. it's also tuned for 93 octane and i currently have 92..so does that matter?

[86FieroSEv6]

Can't really reach the injectors on this engine. There is a test, you will need to fashion two longish jumper wires. Separate the injector subharness connector. Identify the injector pins and power pin. Set up your fuel pressure test gauge. Key up the fuel pressure ( I like to use a switch and a wire from batt. + to the fuel pump test connector as this saves me from running back and forth to the key). Connect one jumper from batt. + to the injector harness key power circuit. Then connect your other jumper to the desired injector circuit and momentarily ground it, you are simulating the injector driver by doing this. I prefer to brush my ground jumper against metal about three times very briefly. While doing this, make note of the amount of pressure loss on the fuel pressure gauge. Bring the fuel pressure back up again and repeat for the other cylinders. Now, mind you don't over do it as you will hydrolock your engine with fuel. I usually do this with the plugs out and the ignition module power connector disconnected so I can crank the engine over to expel any raw fuel during the test. I hope that was understandable, if not, let me know. If you notice that one or more drop very little or not at all, then you will have found your culprit. Check further for subharness or connector damage, if you measured the injector resistance then you would know the status of the sub harness. We did confirm that there is an actual injector signal being delivered to each injector, didn't we?

[bszopi]

If I remember correctly, you replaced your coil packs with ones from a junkyard. That's not really replacing them. Who is to say that the junkyard ones were in any better shape than your original ones. And just because you have new wires, doesn't mean they aren't bad also. Go to a dark area, and with the hood open, start the car, then go look at the wires. If you see what looks like arcs or lightning along any of the wires, they are bad and need to be replaced.

[Rootie524]

well that may be true i just think its odd that a new pack gave me the exact same problem. sure they both could have been screwed but it's just seems like a coincidence to me.

also when the cars running and i removed plugs from the coil pack it gave strong bolts..but like a said some seemed really strong and other just seemed average. and when i just tested it, it was dark out and i did not see the arc/lightning.

where can i get brand new coils besides from the stealership? should i get MSDs..

and is it possible my coil pack is poorly grounded? or there is a problem with the wires going into it? just a thought.

[mickaz]

keep your car GM for the ignition. you played with you wire/spark plugs/coil anmd it returned to normal idle so I think your prob lies there...you need to to remove any variables, like the Junkyard coil, the wires must be ckecked while the car is running and you have to check if the ceramic of one of you spark plug is not cracked.

[Rootie524]

well i had the problem with the old spark plugs and with new ones and i had them out today for the compression test and they looked great. expect for oil on the threads..idk if that's normal.

and i had the problem with my coil pack and ICM AND the junkyard coil pack and ICM...so do i get another junk yard coil pack? it might be the ICM that keeps failing..idk..it might be a bad ground..it might be a loose connection going to the ICM..it might not even be this and it just randomly started working when i fooled with it.

im going to have it start running rough again..then redo what i did and see if it runs better again then ill know for sure where the problem lies.