5.7/auto, engine misses, surges around 1600 rpm, usually at freeway speed with light throttle. starts and runs great, no power loss. I've read possibly intake gasket, but seems to me it would miss through a broader rpm range. Also read it could be injector, which makes a bit more sense. Did full tune up, replaced fuel pump, all filters when i bought rig. #3 and #5 plug were covered in an ash like soot, not black, kinda brownish. After that, it kicked back misfire cylinder 5 code. checked everything, all is good. Compression, plug, wire, cap, rotor. but #5 plug was developing a small bit of that ash again. Read that it could be additives too. more than a dozen tanks of Chevron 89 octane, still the same. Is there any definitive way to check for intake leak, or injector leak/issue. I'm more than capable of changing everything, but don't want to just throw money and parts at this thing if I'm heading down wrong direction. again, runs great except at speeds above 40mph around 1600 rpm with light throttle to accelerate there is a serious miss. Ideas, thoughts, fixes before I throw a ton of money at a cheap fix?

 

YA ! On the intake theres a couple of ways start motor from cold and spray wd-40 around mounting surface slowly if rpm picks up or smooths out thats the spot ! also you can use soapy water pour it on the manifold spray it on the ends same result but truthfully i dont think thats the direction you should go that number 3 and five plug issue might be worth looking into additives do effect plugs and shorten there lifespan you were right there but it would effect them all ! myself i think i would lean toward the possibility of electrical first How did the components look when you pulled them Are you using the right temp range for your plugs you might try a colder plug, How does the intensity of the spark arch look is it weaker on #5 then the rest you can wait till dark then pop the hood and start the car then look for any arching or cross fire from the ignition system if all good there check check fuel presure at test port it should read around and maintain 66 lbs with ignition on 2 sec prime and engine off,if it doesnt then look at fuel pressure regulator, check if egr valve and evap system are improperly funtioning check all vacume lines, cannister i would look into those first and as far as the plugs there might be the possibility of the injectors not functioning properly or carbon build up, here is my cheap 22.95 fix on the injectors and top end, chevy dealerships sell a product called (chevy top end cleaner)! and its little brother (GM fuel injector cleaner) its one of their best kept and most profitable secrets! it comes in arosol cans . all you should need is one can each, to use the injector cleaner ,start and bring car up to normal op. temp. shut it down then unplug your fuel pump relay and pull the fuse to disable pump[,do both on some models there is a oil press override that will activate the fuel pump once the motor builds like 4 lbs of oil press. remove cap from fuel injection pressure connection, it looks like a valve stem for a tire, and should be up toward the front or left side on the (central sequential fuel injection system) or CSFI system or THE SPIDER if you have to ever pull the intake you will see why its called that! Im pretty sure you have this system, screw can onto test connection, this will pressurize your fuel rail activate the injector poppets and allow the car to run until its contents are depleated.start and run the car up through the rpm range to help clean them out, for the top end cleaner simply spray contents of can into the intake while its running let it sit overnight then (change the oil) before you start the car (this is important) , this stuff is strong but its gods gift to top ends it will decarbon your valves, pistons clean the injectors , the whole shooting match !replace fuel pump relay and fuse start the car bring it up to operating temp. as you again go through the rpm range and lol i hope you have good neighbors you will see why ! then take it for a test drive again going through the rpm range under load keep in mind if the battery was disconnected the pcm loses its memory and will run badly for the first few miles it takes anywhere from 5 to 10 miles of different driving situations and conditions before the relearn process is achieved ! alot of system checks and and diagnostics require a full function scanner to run these test and remotely operate components , if you usually do your own work then it might be beneficial to pick one up its worth the 200 or so bucks and it will save you that real fast when replacing parts on these systems i know it has helped me through some hair pulling wat the hell times. OH !Also like to again drain and refill the oil after a few miles , not the filter, but thats my thing just for my own peace of mind that i got it all out i hope this helps good luck man!!
96 BURB 454BB HAMMERGONE

 

thanks for all your input tm4hammer. soon as mother nature calm down, gonna start checkin everything. meantime, sittin here playin couch mechanic. seems to me, from past experience, a vacuum leak would cause high idle, constant misfire. now that's with the non computer rigs, so these new computers not sure about. but a leak is a leak, right? this rig idles perfect, pulls like 9-10hg vacuum on scanner at idle, so my thinkin is no vacuum leak? i can't read the cam offset on my scanner, but with such a smooth idle, i can't be far off. my problem seems to come up only at 45+ mph, only in o/d, and only when about 1/4 throttle lightly applied. now, it almost feels like rearend gears skippin, if you've ever had the displeasure of that experience. it's a fairly hard stumble, but again, it doesn't do it above 2000rpm. it won't do it under 40 mph either. only 45+ at about 1500- maybe 1700 rpm. i can pull hill at 35 all day, in third or fourth gear easy. gonna run that cleaner thru system, double check all plugs, maybe replace again, and replace cap/rotor/wires again. if you or anyone else has any other input, i'll gladly take it. thanks again.

 

Hmmm now im scratching my head too ? Sounds like you followed the right direction thus far ! how many times has it kicked cyl#5 misfire after you cleared the code? have you measured the spark jump at that cyl. you can pick-up a spark tester that can be adjusted to the proper gap for around 6 bucks at most parts stores cheaper than a set a wires and plugs but make sure you do have a quality set of wires on it and they are routed correctly Not sure the top end cleaner will solve the problem but it sure wouldnt hurt and cover a few bases such as contamination is the fuel metering system just make sure its the dealer distributed oem cleaner the parts store ones are crap and a waste of time from my experiance.
here are some conditions that would set the dtc
25 cycles have elapsed since trans shift change
no tp senser dtc
no maf sensor dtc no ic senser dtc
no vs senser dtc
no crankshaft position senser dt
roughroad not detected
the ect is between -6.75 c and 92.2 c
the engian speed between 300rpm and 5600 rpm
system voltage between 9 an16 volts
positive throttle position change is less than 4.9% for 100 msec.
neg. throttle position position change less than 2.9%
and finally A misfire is detetced
if the vcm determines that the misfire is significant enough to impact emissions or cause damage to the catalytic converter after two consecutive trips under the same conditions it wil turn on the MIL and the MIL will flash when misfire is present
A crankshaft position senser can play a big part in this as well as economy priced cheap wires and ignition parts that emit emi 's The speed senser on top the tranny can also cause problems with your torque convertor and other systems rely on its input it would feel like as you described the rear end slipping and all engine controls
but ya! i will try to do a little more digging around that extra info might lead down another path again hope the info helps Always love a challenge as long as its not mine! right .... LOL

 

same here boss. love a good challenge when it ain't mine. i've checked with timing light hooked to #5 wire, that's bout what i've done for that cylinder. timing light flashed, so there's spark. but question is, how good, how consistent. ordered some taylor brand wires, which is what i normally run but didn't this time. gonna change cap/rotor/wires/plugs again, run injector cleaner thru system. also gonna recheck all 4 o2 sensor numbers and compare to specs. if i can find specs. it really is odd tho. that really is the only time is does it, about 1500 rpm and OVER 45 mph. anything under 45 mph, won't do it. only light throttle at highway speed to accelerate. even then it stops when rpm's get above 1700 or so. #5 plug was the only one messed up when i first changed, so gonna do it all over, change wires too this time, reset the codes, and go from there. fingers crossed...

 

I have a 96 K1500 with the 350 Vortec and it has a very similar problem. It misses bad, around 1500 to 1700 it will start and continue all the way up, rpm wise that is. The odd ball thing is that it only happens in winter time and even then it is hit or miss. Also when I go to start it it cranks over more than usual before it catches and starts up. It does not always catch and start up either, it will turn over and backfire and then completely stop the starter but you can here the starter still trying to turn over the motor. Sometimes I am able to get it to start but it just barely does and then it misses real bad. Anyways sounds kind similar to what you are experiencing. I took it to a friend of mine that is a mechanic and he said that it is the injectors and that they are sticking in the cold weather and spraying too much fuel into the motor and so it hydro locks I believe is the word that he used. So I am currently changing the injectors to the new upgrade system so that will change it over to the multi-port style system. Anyways I just got the plenum off and took lunch and read your forum. So I will let you know if that fixes it for my rig.

Valsetz

 

The platinum or gold platinum are the way to go on the plugs, , The cap and rotor i use delco parts, and if you have a few extra bucks laying around use the oem wires while your at the dealership picking up that can of cleaner remember its not injector cleaner its top end cleaner (GM Top End Cleaner) it can be sprayed into the intake i have used it on throttle Body injection as well as multiport,Back to the wires reason being they use the best quality to aviod problems during the warranty period, as i am told, makes perfect sense, but if you want the best all around use Magnecor plug wires thats what i use on my shovelhead, its highly modified with a Dyna single fire HIE ign , dual dyna 3 ohm coils, and a 4 plug setup, at 8.5 to 10 mm they will last the lifetime of the motor and are the racers choice hands down although very pricey, its one of those you get exactly what you pay for type things.check out their website what specs do you need for the o2 sensers conductivity test or ??? let me know and i will check around i also want to look further into the speed sensor and torque convertor thing i mentioned since your last info. said it feels like the rear end slipping! i will try to set aside a little time HAMMERGONE !!

 

I appreciate all your input tm4hammer. Got wires in today, Splitfire, which has always been beyond great for me. gonna get the plugs, cap/rotor tomorrow, change it all out. Here's a twist. The service light went off on it's own. It's done this in the past couple times, went off on it's own, but will come back on after a day or two. there's still a slight miss, so i'm hopin that it will go away after changing everything. the miss at freeway speeds i don't think is torque converter. the rpms don't change, and it just doesn't feel like a tranny slipping. it does feel like a cylinder missing tho. but again, i will take any info, ideas. gonna change everything, scan it, drive it, and will get that cleaner from dealer. thanks again.

 

Almost sounds to me like a lockup converter for the overdrive my Sub does the same thing at those RPM's and speeds but if I put it on cruise control the problem goes away. Just something else to check on i guess. I also have a problem with a really rough running Sub. Over the last couple of months just off idle and up to about 1500 to 1700 RPM the truck runs really rough after about 1700 RPM it clears up and runs like a champ. Yesterday i was on my way to work I stopped at a light and when I stepped on the gas the truck died. After about a Min. or so i got it running again but it ran like it was only on 5 cylinders i limped the thing home and started checking things out and code p0300 random multiple cylinder misfires came up and p1345 Manufacturer spacific came up saying Camshaft to Crankshaft position correlation fault. started troublshooting today and i cant figure it out the thing smokes black as night and i have not been able to drive it cause it runs so rough Cylinder's 5,7and 8 are dead there are no vacume or intake leaks and all cylinders have spark. I just replaced plugs cap rotor fuel filter air filter and replaced wires. After i turn ignition to on possition but not start the truck the fuel line pressurises but bleeds off imediatly. I have heard about the TBI injection unit on my sub going out and having to replace the whole unit for about 300 bucks or so. its a 99 2500 4x4 with a 5.7 but all the manuals i have seen dont have my injection unit in them its all the rail style. i even cut the exhoust apart to see if it would change anything like maybee the Cats causing problems but nothing changed. I personally think its a flat cam but my brother doesnt. I even pulled the Distributor just to check if it may have had a couple of broken teeth on it or something. Everything is back together like its suposed to be but the damn thing still wont run like it used to it has 134,000 miles on it and i kind of figured something like this was gonna happen eventually but this thing has me stumped. I pulled the EGR valve off and cleaned it also. Would a TBI injection unit going bad cause this kind of problem ie, running rich and stumbling

 

Not a problem maxxman let me know if it works by the way it was late, I had a hole in my shoe, the sun was in my eyes, and i was walking barefoot in the snow uphill i made some edits that i screwed up on glad i caught them and i hope you see them GM sells both a top end cleaner which you spray into the throttle body and a fuel injector cleaner which you screw into the test conn. to the fuel rail , my bad !sorry for the mix up! But pick up both! also the spark gap tester will tell you the frequency and intencity of your spark i misprinted the info sorry ! you hook one side to your plug wire and the other to a ground , adjust tester to spec. GM HEI 30 TO 34 ,GM Distributorless 36 to 40 thousand volts, cost around six bucks again sorry for the mix up and hey simpsonracing you might also try that top end cleaner and fuel injection cleaner sounds like you might have sticky leaking fuel injector poppets ! and a few things going on! it sounds alot like a crankshaft position sensor to me the PCM uses the info from this sensor and rpm to determine when to pulse the ign. coil , the fuel injectors and control the timing which would cause all the problems you stated check the terminals and harness, pull the sensor and check the tip for galling or metal shavings, and check the reluctor ring ,do a compression test that will get you a little more info to go on, here are some questions what do your plugs look like , what is your fuel press should read for central sfi 60 to 66 psi running and throttle opened quickly and released. for ign on, 2 second prime press. for central sfi should maintain 66psi and what is the leakdown rate key off, and ok (input sensors) that can also have a direct effect: a broken or loose TPS can cause intermittant bursts of fuel because PCM thinks throttle is moving MAP sensor PCM uses to control fuel and ign. timing MAF sensor PCM uses for fuel delivery, IAT sensor, ECT sensor all relate to PCM control of fuel air mixture, the knock sensor reduces spark knock from heavy detination or pinging this allows engine to use max advance or retard timing depending on knock severity,ox sensors, you should have four of them, CKP sensor,CMP sensor and the VSS sensor, all these take readings and inputs them to the PCM which then determines your air/fuel mix at different speeds and conditions, in addition there are more imputs as well like air cond., batt. voltage, brake on off switch cruise control, egr valve position, oil level and press., evap system, fuel level and tank press., ign. switch, park/neutral switch, sensor signal and ground circuits, and trans, controls remember when you unhook the battery the PCM will lose its memory and the first few miles you drive it will run like crap it takes around five to ten miles of varied driving conditions for the relearn process to be achieved and the next time you want to check your cat or muffler dont cut your exhaust in half LOL if i remember right to test the exhaust system you plug a vacume gauge into a intake vacume source, record vacume at idle, then increase rpm to 2000 and quickly release, record vacume, do this a total of four times,recording each time, on the forth if vacume is 1in less-hg then you had at idle then have a bad cat or restricted muffler so to wrap it up just start with the checks to insure all is mech.in spec.and ok I.E check sensers and harness , clean the top end to decarbon components and run gm's fuel injector cleaner thru the fuel system to clean your injectors good luck
HAMMERGONE!!