Got a miss I cannot find.

O

onebad82z

Member
My daily driver 2000 2.2L/5 speed S10 now and then has a miss. Right above idle (1000-2500rpm give or take) it will miss under load. At idle and light loads it runs perfect. I have owned the truck since new, always maintained now with 217k. I thought it was wires since they has roughly 50k on them, but new ones did not change it. Plugs are fresh with maybe 1k miles on them. It has yet to set a SES light and no codes in the ECM. I have an Actron scanner that verifies the SES light works and no codes are stored.

I Checked the Primary and Secondary resistance of the coil packs hot and cold.

Spec for Primary Resistance = .35-1.50 ohms
Spec for Secondary Resistance= 5,000-10,000 ohms

After sitting in my house @ 74 degrees for nearly 20hrs I have:

Coil Pack 1/4
Primary = .4-.5 ohms
Secondary = 5,650 ohms

Coil Pack 2/3
Primary = .5-.7 ohms
Secondary = 5,710 ohms

Then I put them under the hood over night @ approximately 30 (or less) degrees for nearly 11hrs and I have:

Coil Pack 1/4
Primary = .4-.5 ohms
Secondary = 4,920 ohms

Coil Pack 2/3
Primary = .4-.5 ohms
Secondary = 5,030 ohms

So all findings have the coil packs showing spec resistance figures. I put them back in and the miss remained.

So I threw the new plugs in...she still missed. Kinda leaned towards a failing fuel pump...nope! Brand new fuel pump and filter installed. Blew all lines out with compressed air, no blockage.

Although it does run noticeably better with the new fuel pump, it is still missing. Overall the truck runs great now with all these parts and tune up pieces I have changed so I really feel the money has been well spent. But it still misses! BUT, not as often nor as severe as it was before the fuel pump. I am out of ideas at this point. I may throw in new coil packs as they are the originals and I do like to change coils on my vehicles every 100k or so, so it is overdue by my standards.

Original O2 Sensors. Scanner shows voltages are in spec for what they should be.

Swapped in known good coils off a friends truck that runs mint in all weather. Miss is still there!

Brand new AC Delco TPS... and the miss remains!

I just swapped in a good used set of injectors and fuel pressure regulator. Good used MAP sensor also installed and the miss remains!!! That rules out fuel system. Brand new pump, filter, good used injectors and FPR from a truck that had no miss and the truck runs the same... missing. Lines were all blown clear when pump and filter were swapped. Fuel rail was blown out during injector swap. I also put in a new intake manifold gasket as it had a small leak and I had to pull it to do the injectors anyway so I changed it. All brand new o rings top and bottom on every injector.

I plan to remove any/every ground I find under the hood and clean/grease/reinstall. Other than that I may put in a new crank and cam position sensor as they are fairly cheap enough.

Any ideas?? I have been chasing this since LAST January '09. I have driven the truck like this and put on roughly 10k miles. Still dependable, just misses. Gets good fuel mileage. 27-29 Highway.
 
when tracking down a problem you always need to start with the basics,
have you adjusted the valves and done a compression check recently?
have you verified the cam timing, is ok
the miss may not be electrical, or fuel related, it might be mechanical
obviously a REAL TIME data logging scan tool would be a huge help in locating the source of the problem

this info may help
http://www.corvettebuyers.com/ecm.html

http://www.aldlcable.com/

read

http://members.shaw.ca/corvette86/Component Location View 86.pdf

http://www.digitalcorvettes.com/forums/showthread.php?t=54543

http://forum.grumpysperformance.com/viewtopic.php?f=32&t=596

http://forum.grumpysperformance.com/viewtopic.php?f=32&t=1401

http://forum.grumpysperformance.com/viewtopic.php?f=70&t=986

http://www.digitalcorvettes.com/forums/showthread.php?t=54543

buy

http://www.obd2.com/scantool/scantool.htm

http://www.amazon.com/gp/explorer/B0002KKIAK/2/ref=pd_lpo_ase/102-7445206-4788911?

or (depends on year)

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=46030


YOU REALLY NEED THIS


KNOWING WHAT YOUR DOING IS IMPORTANT, TO GETTING GOOD RESULTS!
no one knows everything about all models and years so it helps to have the correct procedures and info in a handy referace source,now you can get by with a HAYNES or CHILTONS manual, or something similar, but for detailed info, OWNING the CHEVY SHOP MANUAL FOR YOUR SPECIFIC CAR IS ALMOST MANDATORY!
I get asked frequently, "how did you know how to do that?"
well, EXPERIANCE plays a big roll, working on similar cars and engines helps, and the INTERNET is a good resource... but theres ALWAYS a big need for DETAILED REFERANCE MATERIAL, SPECIFICALLY MATCHING YOUR PARTICULAR CAR and if you have not yet invested in a SHOP MANUAL for the year make and model of you pride and joy muscle car your either not serious about your hobby, or most likely NOT A SERIOUS HOT RODDER! I constantly see guys SCREWING up installations, or adjustments,if you don,t know exactly what your doing, you need to either let the dealer do it and PRAY his mechanics are experianced and can read, OR..if your like ME, you would rather do it yourself and KNOW its been done correctly...
if your not aware, heres where to order them....

1-800-782-4356

http://helminc.com/helm/homepage.asp?r=

your average shop manual may cost $100-$150 ONCE! but youll easily save far more than that in reduced time and screw ups in under a years time or in many cases on one job vs having the dealer do the work!
 
grumpyvette said:
when tracking down a problem you always need to start with the basics,
have you adjusted the valves and done a compression check recently?
have you verified the cam timing, is ok
the miss may not be electrical, or fuel related, it might be mechanical
obviously a REAL TIME data logging scan tool would be a huge help in locating the source of the problem
Click to expand...

Have not adjusted valves. Will look into how so. Not sure if it is like a hydraulic FT cam sbc. That case I am good. Compression test shows maximum 8% difference from worst to best cylinder. Cam timing is a good one. Original timing chain and tensioner. That is to be replaced this weekend if I get the time. I know it is loose as it is making some racket. Convinced it isn't fuel, electrical or mechanical is definite.
 
tracking down a intermittent problem is ALWAYS a P.I.T.A.
you can,t rule out anything yet, it might be as simple as water in the fuel or a bad ground, or a bad electrical connector or sensor,it can be something major like the computer controls, the ECU,the connectors or the sensors or something minor like a bad ground, but it can be something really difficult to locate, that only happens when two different things happen at the same time, I had a miss like that once that was caused by a carb that only malfunctioned on hot days if I hit the brakes real hard, I only located the cause after rebuilding the carb, AND finding a vacuum leak in the brake booster, I won,t get into details , but crud in a carb and intermittent vacuum can mess with your mind when your low on experience and only about 20 years old, todays real time data logging scan tools make this far less of a guessing game, try to determine if its ignition or fuel related as that narrows the suspected source of the problem

viewtopic.php?f=50&t=609&p=5672#p5672

viewtopic.php?f=32&t=1401
 
Well I have sunday set aside to get the new timing set & tensioner installed. Also, I have printed out all the wiring diagrams and layed them all out side by side tracking down all of the grounds. I found a few on the block that don't look nice so a new addition to my attack plan is to replace all grounds underhood. Ones that aren't too bad I will just clean up and reinstall. I used the diagrams to be sure I know where they all are.

Driving it the other day I realize it only misses at certain throttle positions. I can let off or nail it when it is missing and it goes right away. I can even let off from WOT slowly and get it to miss. Would scream TPS to me had I not installed a brand new one. So my other thought was there was possibly a bad spot of the throttle shaft of the TB, kinda like an old carb will start to weap/leak after years of use at the throttle shafts. So I grabbed my spare and tossed it on last night hoping... No go. So that rules out one more idea and also a possible bad brand new TPS as even with the spare TB and unknown TPS on it the miss remains...
 
grumpyvette said:
http://forum.grumpysperformance.com/viewtopic.php?f=32&t=168

Im assuming you've set the TPS with a meter and cleaned the IAC carefully and verified no vacuum leaks
Click to expand...

TPS is not adjustable. IAC is spotless.

Ok a new twist here. On the way home from work (50 mile ride) I was able to move the pedal around and get it to miss. Under load it is much more apparent as to be expected. But I would tend to think after a 50 mile ride where it missed the majority of the miles I could get it to set a SES light. NO such luck. So when I got home I unplugged sensors to see if it would come on. Mind you when I start the truck I look to be sure it comes on so I know for a fact that it works. So I unplugged the IAC sensor, noticeable difference in the idle.. much lower and rougher. I then proceeded o to unplug the AIT sensor. Immediate change in RPM's. I then let it idle for 5 minutes or so and then drove it around the neighborhood. Although running bad and trying to stall from the IAC being unplugged it would not set a SES light. OK I'll go one more and unplugged the TPS. Figured at this point the ECM will have no choice but to start screaming. No go. It was running very badly at this point but NO SES LIGHT. How do you test for a bad ECM/PCM??
 
most larger dealerships have diagnostic computers that can test your CPU,
and that cars old enough that some local salvage yards can probably supply a replacement, very reasonably, that you can use to test/replace your current cpu, but before Id go that route ID try to find and use a real time data logger and cable to use to isolate the exact cause


the action ID suggest is to beg,borrow, buy, a scanner that puts out real time data logs, and have the wife or a buddy drive while YOU watch the data on a LAP TOP , or have a dealer do it for you

http://www.etoolcart.com/autoxray-scanner-ez-scan-ax6000.aspx

http://www.auterraweb.com/dynoscan.html

http://www.mercedesmanuals.com/Live_Data_OBD2_Deluxe_Automotive_CAN_BUS_Code_Scan_p/u581.htm

http://www.obd-2.com/

http://www.moates.net/product_info.php? ... ucts_id=54

http://tunertools.com/proddetail.asp?pr ... CMSCAN-KEY

http://www.scantool.net/

http://tunertools.com/proddetail.asp?pr ... ata-Logger

http://www.innovationhouse.com/products ... _tool.html
 
Ok been away from the truck tending to other matters of life. I did manage to put the new timing set and tensioner in. Didn't really feel it was the cause of the missit just needed to be changed as the original had 217k on it. Surprised to find very little wear in it when pulled off. Tensioner was in just as good of shape.

Yesterdays notes: 10.13.09

Anyway... I have some data. I have alot recorded from this morning that I have to type out that I will do later tonight but I noticed this trend this morning.

IGN ADV stays rock solid during miss

MAP values stay rock solid during miss

ENGINE RPM varies (obviously)

ST FTRM spikes to about 10-12% at beginning of miss then tapers off

LT FTRM will eventually move to 10-12% to bring the ST FTRM back to 0% after the miss has been going for awhile

Todays notes: 10.14.09

BUT... just this morning I decided to focus on TPS and I found a trend. At a steady state cruise between 60-70MPH it misses between 24% and 30% ABSLT TPS. But, if I am not watching the scanner (eyes on the road) and I drive as normal and I start to feel it miss I look at the scanner and it is always at 27%. Now with in town driving (get to do both on my daily grind) sitting at a red light and take off normal it will miss between 26% and 32% depending on how heavily I accelerate. But again on a normal take off I feel it miss... bang 27%! Now it also misses on acceleration or deceleration in the same range. Cruising along at anything over 30% and slowly roll out of the throttle and let it get down to 29% or so and she goes to missing all the way down to high 24%'s and then it will clear up. I have swapped between 2 totally different TB's both with different TPS and IAC sensors. No difference in the miss.

I did not watch MAP values today. Yesterday I did watch them for a period on the ride in and they stay solid even when it misses. There is no variation. MAP has been changed with a known good sensor with no change.

Still no SES light. Been meaning to unplug the IAT for the ride in or home to see if an extended drive will bring the light on. It does work as I look for it each time I start the truck.

I was thinking a ground issue but not so much after watching TPS this AM. Between having that bad spot in TPS travel and no SES light yet could this be signs of a bad ECM? I can't see a ground causing a miss in the same spot every time. Now if it missed all the time I could. I will say I plan to check all grounds anyway just to be 100% sure of them.
 
Did want to add... on take off I tend to rev the throttle a few times before I start letting the clutch out. More or less just "blip" it a few times to get the revs up some as the lil 4 banger is too weak to take off from a dead idle. So I do notice that when doing this this morning I could feel it miss in each little "blip". So with that known and the fact it will miss on deceleration in the same range as acceleration I want to think it is not a load based problem correct? I tried to rev it in neutral from a dead idle slowly to the 24% to 27% range but will rev pretty high (like 5k RPM and higher) so I gave up on that idea.
 
NEW ECM FIXED IT!

She runs better than new and not a hint off a miss at any throttle position!

Took 11 months and 14k miles to track this one down!
 
thanks for posting the results, so many guys fail to do that and it leaves a huge void, in our knowledge.
 
Check all your sensor connections, check your grounds, check for water in bottom of fuel tank, check fusible links, Check for air leaks(use propane torch) Check for proper torque on your spark plugs(escaping compression) Get a Field service Manual(Read IT!) Check Pickups on distributor also check module and dielectric grease under module and rotor button look for arcing Ohm check injectors hot and cold, properly route plug wires making sure #5 and # 7 are routed at least 1" from each other make sure battery is fully charged and holding do the Basics that Grumpy listed (None of these are in any order) Start with the basic easiest tests first then move to the next harder in that order most FSM's have a flowchart to follow,dont skip steps, Just my 2 cents Hope you figure it out but given the amount of time Since you last posted I'm assuming you've abandoned this post.
 
Thank you for the additional tips!

I know where you are coming from... but no #5 or 7 cylinder, truck only has 4.

Look up 2 posts it is fixed with a new ECM. I have since put on an additional 10k miles and she has never run better. 230k to date!
 
Congrats..I did'n't see the second page but I kept writing ideas for any one else who reads the posts. Glad to see you got her running good!
 
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