03-05-2000, 09:43 PM
My '87 chevy pick-up loads up at low RPM's. I can't figure it out. I'm thinking of a carb., but I like the EFI. Any help would be appreciated. It has been on a diagnostic computer.<br>firstname.lastname@example.org<br>
What came up when it was on the computer, any codes? If it's loading up it may be possible that the throttle position sensor is malfunctioning or maybe a fuel pump problem. How are the emissions?
03-07-2000, 10:14 PM
When it was on the scanner,the coolant temp sender,and map sensor should have been the first suspects.It takes a good mechanic to read the data stream correctly and match up the actual readings you see,then he has to know what reading is off,even by a little,by confirming every sensor reading with a scale reference. The coolant temp sender can go out of range,telling the computer that it is 40 below instead of 30 above,the comp. adds fuel to compensate,then its to rich.The MAP sensor has a vacuum line hooked to it.Make sure it's not cracked or broken.Put your finger over it while it's running to be sure you have vacuum at the sensor.I have seen the vacuum line in the TBI unit get carboned up on high milage trucks.it will interpret the low vacuum as high load,heavy throttle,and will run way rich.It wont throw a code unless its out of range,and full throttle(no vacuum)is in range,so no code.To test that quick,just grab another manifold vac. line and plug it into map sensor,start it up and see if its fixed.TPS readings on the scanner should be about .60 volts at idle and about 4.0 volts at WOT.With the key on engine off,and scanner hooked up,you can slowly press throttle and watch TPS readings go up,the voltage should go up slowly and not jump up in big increments.A bad TPS will trigger the ECM to throw a code and then go into a backup mode that runs better than yours is.Its backup sensor is the MAP sensor.I highly doubt it is the TPS,check MAP and CTS first.A CTS is cheap,under 20 bucks,if you want to take a chance with it.If you unplug it,and it runs better without it(backup fuel mode),then you have found problem.If not,clear codes,unhook batt. for 1 minute and keep looking. <p>----------<br>John D<br>
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