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97 GMC 1/2ton cargo 4.3 ltr Multiple Symptoms, all related?
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RugRat39
New User
Sep 1, 2012, 7:21 PM
Post #1 of 7
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97 GMC 1/2ton cargo 4.3 ltr Multiple Symptoms, all related?
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115,000 total miles and has been running fantastic for the last 15,000 or since I bought her. About 4or5 weeks ago I noticed a come and go miss on the freeway once overdrive would engage and pedal pressure was light and minimal while maintaining speeds of 65-85mph. I also noticed that while the miss was occuring, the speedo needle would bounce up 5 to 10mph and then back to actual speed continuously, but only when the engine was missing. The miss(more like a slght hiccup) was a soft back and forth kind of gas on gas off motion that I could mostly feel in the pedal and floorboard while any passenger rarely felt a thing. At 1st it occured 1 out of every 5or6 freeway trips. It seemed to be prety minor, felt a bit the way a lawn mower starts to feel about 30 seconds from an empty gas tank. I thought maybe some bad gas or some sediment kicked up in the tank. After a week or 2 it was happening almost every trip and becoming a bit more obvious and a little less soft. I changed the fuel filter the oil, I added power steering & trans-fluid because they were a bit low. I noticed the trans pan was covered with fluid and assume the gasket is leaking a bit but not enough to leave spots on my driveway, and a half quart of fluid seemed to get the mark on the stick. Next morning my commute too work was 110miles and the van ran great the whole time. Different story on the trip home and after 10 miles I'm beginning to worry if I'm gonna have to get a tow due to the now constant and much more noticeable and defined hiccup which was occuring sometimes every 10 seconds yet sometimes not for 5 minutes or so and when it missed it would go on for sometimes a quick 1 second cough and then a random 10-15 second bout of hacking. I did'nt notice any pattern to the hiccups(misses), some longer and some short. When I got off the expressway about a mile or so from home, I stopped at the top of the ramp to hang a right and realised that the trans had failed to drop down to a lower gear after the longer than usual freeway drive. Again I came to a complete stop, but this time shifted to 1st gear, I immediately noticed I could only get 2nd, and also that although i had do drop down manually to get going, i could shift immediately to D and the trans would shift automatically again at the proper RPM. The next day I'm pretty sure I stopped getting the highest gear also. And soon after that I noticed an occasional hard shift into 3rd that seems to come later than it should. Well pretty much all the same stuff still happening today, but the trans has always worked as expected when it's cool(after shutting off for an hour or more)and even then only for 10 mins at the most, this is the only time it gets 1st or 4th gear. Im good with tools but certainly not a mechanic. A fella at the local parts store said he was bettin' its the oxygen sensor. I have'nt a clue and would appreciate any help or insight from all that wish to contribute. I apologize for the book but I've found the best way to show something that can't be seen is with a lotta details. Thanx for your time.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Sep 2, 2012, 7:17 AM
Post #2 of 7
(1693 views)
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Re: 97 GMC 1/2ton cargo 4.3 ltr Multiple Symptoms, all related?
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Get a thorough code reading. Post the #s. 1997 should have some info pending even if no check engine light is lit,
T
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Discretesignals
Ultimate Carjunky
/ Moderator
Sep 2, 2012, 7:53 AM
Post #3 of 7
(1686 views)
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Re: 97 GMC 1/2ton cargo 4.3 ltr Multiple Symptoms, all related?
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My gosh. My eyes. That was some tough reading...
What does the fluid look like for the transmission? Probably wouldn't be a bad idea to drop the transmission pan and change the filter. While your in there you can see what is laying on the bottom of the pan.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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RugRat39
New User
Sep 2, 2012, 10:30 AM
Post #4 of 7
(1677 views)
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Re: 97 GMC 1/2ton cargo 4.3 ltr Multiple Symptoms, all related?
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Here are the codes in the order they came up; P0143-O2 sensor, P0300-cylinder misfire vac leak, P0420-catalyctic converter, P0785-shift timing malfunction. P0143,P0300, and P0785 came up twice. Where should I start? Trans fluid looks good. New plugs and wires 10,000 miles ago and has run beautifully until recent.
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RugRat39
New User
Sep 2, 2012, 10:35 AM
Post #5 of 7
(1675 views)
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Re: 97 GMC 1/2ton cargo 4.3 ltr Multiple Symptoms, all related?
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Forgot to add that the check engine ligh is NOT on.
(This post was edited by RugRat39 on Sep 2, 2012, 10:46 AM)
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Discretesignals
Ultimate Carjunky
/ Moderator
Sep 2, 2012, 10:54 AM
Post #6 of 7
(1671 views)
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Re: 97 GMC 1/2ton cargo 4.3 ltr Multiple Symptoms, all related?
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Does the check engine light prove out when you turn the ignition on? Someone could of disabled the light.
You have multiple cylinders misfiring, so you need to figure out which ones are skipping. You have to use a scan tool that can look at current and history misfire information. You need to know which ones are acting up, so you can get some direction.
If the cat is gone, then for sure the P420 is going to appear.
P0785 is a circuit code for the 3-2 shift solenoid. The PCM/VCM is detecting a short or open in the circuit. The circuit has to be checked out using a DMM or scope to see what is going on.
Here are some of the things the PCM/VCM will do when it detects a circuit problem with that solenoid:
ACTION TAKEN WHEN THE DTC SETS
^ The VCM commands a soft landing to third gear.
^ The VCM commands maximum line pressure.
^ The VCM freezes shift adapts from being updated.
^ The VCM inhibits TCC engagement.
^ The VCM inhibits 4th gear if the transmission is in hot mode.
^ The VCM illuminates the Malfunction Indicator Lamp (MIL).
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Sep 2, 2012, 10:56 AM)
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RugRat39
New User
Sep 2, 2012, 11:14 AM
Post #7 of 7
(1661 views)
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Re: 97 GMC 1/2ton cargo 4.3 ltr Multiple Symptoms, all related?
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Converter is there. thanx for help. Misfires on all cylinders ranging from 21,000 down to around 5000.
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