91 suburban has me baffled, any ideas?
September 13th, 2014, 10:14 AM
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91 suburban has me baffled, any ideas?
I have a 91 suburban 5.7 throttle body. The suburban will run great at idle, i can rap it up and be fine but as soon as i put it in gear it acts like the timing is off and runs horrible... i have replaced the injectors, fuel regulator valve, fuel pump, fuel filter, spark plugs,wires, cap, rotor, distributor, throttle positioning sensor, idle air control valve, map sensor, water pump, thermostat.... the truck has codes for low voltage on map sensor... im curious if there is some kind of vacuum line connected to the transmission because it acts like a vacuum leak or bad timing...
September 14th, 2014, 5:51 PM
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If i was you i'd fix that code first cause the map sensor is the load sensor for the system-big input!
Make sure the vacuum line is connected to engine manifold vacuum,common failure.The voltage reading should be about .5-1.5 volts on the signal wire while the engine is idling. The signal wire is the one in the middle. If you have a reading out side of that you could have a bad sensor or vacuum line thats not hooked up right and would have to also verify good 5 volt reference voltage to pin c of the connector and a good ground on pin A of the connector! But i would try to get that code for the map fixed first before i'd try anything else! As you give it gas the voltage reading should rise smoothly with the rpm.
Make sure the vacuum line is connected to engine manifold vacuum,common failure.The voltage reading should be about .5-1.5 volts on the signal wire while the engine is idling. The signal wire is the one in the middle. If you have a reading out side of that you could have a bad sensor or vacuum line thats not hooked up right and would have to also verify good 5 volt reference voltage to pin c of the connector and a good ground on pin A of the connector! But i would try to get that code for the map fixed first before i'd try anything else! As you give it gas the voltage reading should rise smoothly with the rpm.
September 14th, 2014, 8:47 PM
#3
ughg i'm sorry to hear you threw that much time and money on parts that maybe never needed to be changed during life of car. that's how we learn sometimes.
use your diagnosis skills to decide which part you do NOT need to test. always check a part (test) and if it works: put it back. by hook or by crook (avoid pulling part to do a full test if you can think it through). horse sense.
you haven't been too specific yet on loss of power. ie, if you rev engine is it smooth? if no, maybe diagnose your intake gasket for leaks next.
your trans may send signals to and from the PCM (spark ignition module / timer). and if your trans's computer is bad it could cause problems (as could bad ground or connectors to it). on the other hand rough engangment (ie, wacky solenoid, deteriorated belt) could be what your experiencing. but on a 1991 maybe you need a dealer ODB tool to talk to trans module.
need more details how when/how
last post said MAF i'd expect to get warnings when reving on that (more air, flow meter, should effect). but i'm not familiar with that model. throttle body programming cause havoc on some cars: don't know if your car even has one!
i think your trans observation is interesting. have someone else listed to car see if they get same impression.
air, spark, fuel (and sometiems trans). always check codes and when one does always check all ODB stuff reports good: exactly why is for problems like you seem to have. you can't decide about a/f/s if a computer connector is off.
i almost don't want to say O2 sensor since it's so hard to tell from cat (read many articles!) and so expensive to be wrong on
use your diagnosis skills to decide which part you do NOT need to test. always check a part (test) and if it works: put it back. by hook or by crook (avoid pulling part to do a full test if you can think it through). horse sense.
you haven't been too specific yet on loss of power. ie, if you rev engine is it smooth? if no, maybe diagnose your intake gasket for leaks next.
your trans may send signals to and from the PCM (spark ignition module / timer). and if your trans's computer is bad it could cause problems (as could bad ground or connectors to it). on the other hand rough engangment (ie, wacky solenoid, deteriorated belt) could be what your experiencing. but on a 1991 maybe you need a dealer ODB tool to talk to trans module.
need more details how when/how
last post said MAF i'd expect to get warnings when reving on that (more air, flow meter, should effect). but i'm not familiar with that model. throttle body programming cause havoc on some cars: don't know if your car even has one!
i think your trans observation is interesting. have someone else listed to car see if they get same impression.
air, spark, fuel (and sometiems trans). always check codes and when one does always check all ODB stuff reports good: exactly why is for problems like you seem to have. you can't decide about a/f/s if a computer connector is off.
i almost don't want to say O2 sensor since it's so hard to tell from cat (read many articles!) and so expensive to be wrong on
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