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73-87 Chevy _ GMC Trucks => Performance => Topic started by: 1MCP7.3/87GMC on November 06, 2011, 01:16:21 am
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Ok so I have an 87 gmc tbi the truck runs great when the motors not up to temp but once up to 180 it runs like a dog with no power it failed the smog check due to it is there a sensor that could be bad that is causing this to happen. At the 15mph test it passes good at 25 it fails even adjusting timing didn't help it pass like last year. Thanks in advance for any information oh and the computer is new and ive ran the test with hypertech chip and with the factory chip same results also new catalytic converter and 3 styles of O2 sensors. Also tried 160 degree thermostat and 195 but the 160 failed because it wasn't up to temp according to the state of CA the 195 failed the same as the 180. It's not that I'm worried about smoging but I would like to get it running better.
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You need a 195 stat. Are you getting any codes?
Other than low power are there other symptoms? Need more info.
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We tried a 195 it ran worse then the 180 degree did. No codes, at first it was a code for o2 sensor but after that was replaced it still ran the same we replaced it 3 times in hopes that it was faulty we tried Bosch, and the oriley brand then I went and got one from GM all had same results. But after the first replacement the code went away a very good mechanic worked on it for a week and tried all he knew to try, with no luck he put it on the computer but nothing came up wrong. It acts like vapor lock when it starts running bad but it's getting to much fuel not the opposite. And this has happened over a 2 year period when I got the truck it ran SUPER good. Also idk if it has anything to help but I did a full tune up on it and the coil modgular was replaced.
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How about your EGR valve?
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That's also replaced
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Still need more info, If it ran great when you got it, what has changes since then and what have you replaced since then..
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It had an issue with a coil modular that failed and caused detonation in the exhaust, shortly after that the Cat was replaced. Well nothing motor wise has changed EGR, tune up plugs gapped at correct settings. Alternator was replaced also. Thermostat replaced 3 times 160,195, now has 180. No engine codes o2 sensor replaced 3 times high quality GM one on here now. New computer ran one test with hypertech chip and then a stock chip no real change. Had a TB spacer but it was removed after it failed the first time after it was removed it failed again. Before the smog failed the rims and tires changed from 33 to 32.5 rear end gears replaced with same ratio I mean I don't think anything else is relevant like the billet grill and push bar.
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coil modgulator=igntion module???
How about posting the #'s from the testing. If you post these we can help pin point the problem
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Ok sorry it took me so long to get back to you on those numbers but I work about 100 miles away from home and just got around to the truck to get the numbers.
15MPH TEST rpm 1408 %CO2-14.3 HC max 125 MEAS- 48 CO% MAX .79 MEAS-.67 NO MAX-1062 MEAS-4 ALL 15MPH PASS
25MPH TEST RPM 1377 %CO2-12.9 HC MAX 96 MEAS 118 CO% MAX 1.00 MEAS-2.57 NO MAX-1073 MEAS-12 GROSS POLLUTER FAIL!!
the underlined are my numbers max is what I have to bring it down too, as you can see im close on HC but on CO im WAY high
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Got access to a scan tool? What's fuel integrator and block learn at?
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I don't have access to a scan tool but what is fuel integrator and block learn? And what can I do to change them?
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Fuel Integrator is the short term adjustments to the fuel. Block learn are the longer term adjustments based on how well the engine is running both are based on feedback from the oxygen sensor(s). If everything is running and working perfectly then both numbers will be 128.
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I would suspect low fuel pressure or a vacuum leak based on those numbers. ( I admit it's been awhile since I looked at emission #'s for troubleshooting though)
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You can make a cable and use winaldl to read the output on the TBI trucks.
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Your CO is High your HC is high your NOx is low your CO2 is low too bad they don't include the O2 reading. You are indicating rich though due to the high CO and you have some non combusted fuel with the high HC number which could be caused by several things. If you were lean the NOx level would be higher CO would be lower. Here's what you need to check:
Make sure the air filter isn't clogeed and check your O2 sensor. Get datastream and we can nail it down for sure but check for codes in the meantime. All you need is a paper clip. Let's also assume the truck is properly tuned and running well.
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All I need is a paper clip? Before testing I ran 91 octane a few tanks before did a full tune up and that did include a new air cleaner. Also would a scan tool be something auto zone or oriely would rent or are they relatively cheap and buying it be better?
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You just need a paperclip in the AB slot to pull the codes.
For getting the other info, use this:
http://winaldl.joby.se/
This is mine:
http://forum.73-87chevytrucks.com/smforum/index.php/topic,7711.msg47384.html#msg47384
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I bought mine scanner at Checker for 29 bucks,very good investment.
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I'm just throwing out a suggestion.
Are you running headers? If so, the factory oxygen sensor is not self heated, meaning it only reaches operating temp by way of exhaust heat. Sometimes the headers place the sensor to far to reach optimal temp. This along with the fact that your running a lower temp stat could be the issue. A 3 wire O2 sensor will fix this. One wire for the factory hook up, one negative, and one switched power source.
my 2 cents.
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Running factory manifolds and the temp is only the 180 because it smoged cleaner then the 195 did.
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You really need to check fuel pressure KOEO, KOER, and KOEO with the return line blocked. This will give you a good idea of the health of your pump, regulator, and injectors. Barring any issues there, I would say it could be a bad TPS or MAP sensor causing the ECM to miscalculate load percentages. Without any datastream info to back it up, it's just shots in the dark though.