Scanner worked once, but now can't connect?...

[Ricky B]

Hey Folks, hopefully this is an easy one to answer----Daughter's '96 with the 4.0 OHV was acting up a bit (rough idle, some bucking, stumbling on take off, slight power loss) after a rebuilt tranny was installed. CEL would come on occasionally. So I hooked up my Innova 3130 scanner and noticed a stored code or two---but unfortunately I didn't write them before I cleared them. Yeah, I know, dumb me, though the truck did seem to run a bit better.

Anyways I got back into her the other day-----pulled the (Autolite 105's) plugs, re-gapped them to .054, replaced the fan belt, replaced the PCV, ran a vacuum test (passed nicely, 18.6---19.3 Hg's at idle), replaced the rail mounted fuel filter and the air filter. Truck now runs even better than before, but I still have a stumble when taking off or somewhat 'mediumly' stomping on the pedal. But no CEL at the moment. Decided to run a 'live test' with the scanner-----and now it won't read the truck (i.e. Unable To Establish Link To Vehicle). I've tried this five different times, physically holding the female scanner plug first one way, then another, 'cuz it fits a bit loose). Still nothing, so I called Innova's tech line, and they told me to check for blown fuses, and to also try the scanner with the batteries removed. Found only one blown Maxi fuse (far drivers side, fourth one down, 20 amp, Trailer Park LP/Trailer Stop LP). Replaced it and tried two more times.....and still the truck will not connect to the scanner.


Any hot tips here on what to do next?.....

 

[Maniak]

Does the CEL turn on when you turn the key to the "on" position and then turn off once you start cranking?

If your not getting it then, your having some kind of ECU/power issue. The fuse that I've gotten burned on a few times is the Cig lighter fuse. I've run into 2 vehicles that when that fuse blows you can't talk to the ECM (although it is working).

~Mark

 

[Ricky B]

Does the CEL turn on when you turn the key to the "on" position and then turn off once you start cranking?

If your not getting it then, your having some kind of ECU/power issue. The fuse that I've gotten burned on a few times is the Cig lighter fuse. I've run into 2 vehicles that when that fuse blows you can't talk to the ECM (although it is working).

~Mark

1). Yeah Mark, I've heard that too---but the cigarette lighter fuse is good (#17, 15 amp).

2). Will try that right now and verify.

3). Thanx.....


*EDIT*...CEL comes on with key on RUN, goes right out after engine starts....and stays off.

 

[Ricky B]

Alright, a quick update for anyone here who cares;

1). Seafoam thru the throttle body. Let it marinate for 3 hours, had a nice long lasting cloud(s) of smoke after running her again. Idle seemed to tighten up a bit.

2). Drove to gas station, added 5 gallons of Chevron 91 octane to the two gallons that were still in the tank. No difference in drive-ability on the way home.

3). Inspected & tested MAF, TPS, IAT and ECT. All of them look near new and spec'd out perfectly.

4). Started up truck and it was idling very rough---rough enough to set off the CEL. Perfect, that's what I wanted. But just before shutting off the engine to hook up the scanner, I heard a new faint, odd 'tappng' sound. Lookin at the driver's side of the engine, face down low, I revved the throttle and the tapping got quicker----and that's when I saw the spark shooting from the #5 spark plug boot to the engine block. Hmmmm.

5). Shut off engine and hooked up scanner. This time it 'connected' with the vehicle ('cuz the CEL had come on?) but said there were no stored codes. But the yellow emission light was on, indicating an impending code/problem/issue with the vehicle was on the way. Hmmm.

6). After the engine cooled I pulled out the #5 plug, and found two hairline cracks in the porcelin insulator. My new AC Delco plugs will be here in a couple of hours, so I'll report back what happens after I swap them all out.....

 

[Ricky B]

Alright Kidz, one more update;



1). Replaced all 6 plugs with new AC Delcos #41-396's, gapped at .057". And now this gal idles, sounds & runs like a striped-a$$-ape. And I mean like very close to factory new-----simply amazing.

2). The CEL that came on earlier today went away. Hooked up the scanner one more time after changing the plugs-----and now it won't 'connect to the vehicle' again. This is still very weird to me----I don't understand why it will 'connect' when there's a CEL on....but fails to connect and give you any information (past or present) after the CEL goes away? Though it will on our '96 Suburban. Very strange....and which is why I started this thread in the first place. Any of you Rok Starz here have a clue on why that is?


3). And finally, I want to remind all of you younger Kidz here (just as my Dad did to me about 40 years ago) that it's almost ALWAYS something stupid & cheap that's causing your problems. And in my case that's exactly what it was----just two tiny cracks in a five dollar spark plug that created a giant driveability problem. So make it a habit to start looking at the dumb, easy things first whenever you suddenly have a problem with your vehicle. And then, SLOWLY work your way thru the diagnostic process----before throwing money at parts, or a mechanic, or the dealership. 'Cuz nine times out of ten, you'll solve your problem.

4). Finally, I know I kind of 'jacked my own thread but hopefully there's some decent info/tips/ideas that might help some of you in the future.....

4)