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Need Referal to discussion board for 94 5.7 problem
- Thread starter stano
- Start date
oh sow we arnt good for you ha.
just ask the tbi system is all about the same on them.
just ask the tbi system is all about the same on them.
Sounds like egr to me.
have you taken a scanner and watched the tps values? there needs to be a good smoth clime in the numbers and no dead spots. also find out the min and max range for the at idel value. it might be out of range just a bit but not to the point to kick a code.
Well I think there is a lot of talent here from guys with hands on. (the best kind) here goes..
We have a 1994 C1500 Two wheel 5.7 auto (700R4) with 3.42 gear, it also has catback duals exhaust. This truck appears to be well maintained. My daughters truck. It has a short stumble when you step on the gas in park or drive. If you are in over drive and about 900 to 1300 rpms and accellerate it sometimes stumbles and jolts the whole drive train for a second and then takes off.
We have given the truck a tune up of new plugs, wires, rotor, cap, and air cleaner. The old plugs were very bad with a whiter color of much hard build up, mostly on plug number 1 and also on plug number 8, the rest were not as bad. There is evidence of an intake gasket change and we figured the white build up may has came from the water leak?????The truck does not show evidence of leaking water now.
Also we have a scanner I think is a auto xray 240. It is for 83 and up to ?????. It did give up operations and monitor the operations on the 94 truck. We found in section called MANIFOLD AIR TMP was a value of -40.0 degrees. We get this reading when we did two tests, one at start up and the second after reaching 195 degrees, warn up. so we went to a friend at chevy garage and he said the manifold temp sensor must be disconected and look for a purple and blue wire. So we did and found the connector taped to the wiring harnes near the EGR valve with grey tape and nothing connected to it, we did not find a sensor on the tube to the air cleaner or a sensor between the aircleaner and the thoutle body or on the intake. so back to chevy garage to the parts guy and looked at picture and found no sensor for 94 and he said only diesel had sensor not 5.7 gas engines. He also said maybe to disregard the -40.0 degree reading????
So I not real sure about the reading of -40.0 dgress from the comp yet but we think we may have to look further.
We can give you the values of the two scans.
any ideas what to do next. and anybody have an idea about the -40.0 degrees.
thank you
stano 87K5
We have a 1994 C1500 Two wheel 5.7 auto (700R4) with 3.42 gear, it also has catback duals exhaust. This truck appears to be well maintained. My daughters truck. It has a short stumble when you step on the gas in park or drive. If you are in over drive and about 900 to 1300 rpms and accellerate it sometimes stumbles and jolts the whole drive train for a second and then takes off.
We have given the truck a tune up of new plugs, wires, rotor, cap, and air cleaner. The old plugs were very bad with a whiter color of much hard build up, mostly on plug number 1 and also on plug number 8, the rest were not as bad. There is evidence of an intake gasket change and we figured the white build up may has came from the water leak?????The truck does not show evidence of leaking water now.
Also we have a scanner I think is a auto xray 240. It is for 83 and up to ?????. It did give up operations and monitor the operations on the 94 truck. We found in section called MANIFOLD AIR TMP was a value of -40.0 degrees. We get this reading when we did two tests, one at start up and the second after reaching 195 degrees, warn up. so we went to a friend at chevy garage and he said the manifold temp sensor must be disconected and look for a purple and blue wire. So we did and found the connector taped to the wiring harnes near the EGR valve with grey tape and nothing connected to it, we did not find a sensor on the tube to the air cleaner or a sensor between the aircleaner and the thoutle body or on the intake. so back to chevy garage to the parts guy and looked at picture and found no sensor for 94 and he said only diesel had sensor not 5.7 gas engines. He also said maybe to disregard the -40.0 degree reading????
So I not real sure about the reading of -40.0 dgress from the comp yet but we think we may have to look further.
We can give you the values of the two scans.
any ideas what to do next. and anybody have an idea about the -40.0 degrees.
thank you
stano 87K5
Also check the IAC / minimum air adjustment. If you don't have minimum air set correctly, the IAC cannot accomodate for when you step on the gas, and will cause a slight stumble.
Take the IAC right out of the housing, and without forcing the needle to move, clean off the pintle, then the entire IAC housing of any and all carbon deposits from the PVC.
Put the IAC back in, then set minimum air. This is done by starting the truck, and letting it get to full operating temperature, then shutting the engine off and jumpering the two pins at the top right of the ALDL connector (white wire with a black stripe, and a black wire with a white stripe) turning the key to on, but not starting the truck, and waiting for at least 30 seconds to ensure that the IAC has the pintle all the way shut against the IAC housing. Once that is finished, unplug the IAC, pull the jumper out, and start the engine again, wait about 5 minutes for it to get back to full running temp if you took too long, punch out the little cap that protects the idle adjustment screw, then use a torx bit to back the idle off / advance it until it is at about 450 - 500 rpm or so in drive. (make sure to chalk the wheels, and set the parking brake before you get out of the vehicle with it in drive) Make sure that you don't set the idle up high enough for it to overcome the emergency brake, or the wheel chalks. Once you've got your minimum air set, go back inside the truck, turn it off, then go back to the front, plug the IAC back in, then turn the truck to ON again, without starting it, adjust the TPS so it is at about .54 volts at an idle, then unplug the negative battery terminal for approx 1 minute to reset any codes the ECM may have thrown with regards to the unplugged IAC. Start the truck back up, and without letting it idle for a while, take it for a 20 minute run. Make sure that the ECM experiences at least one second gear downshift, so it is able to use it's learning protocols across all the RPM vs MAP bands.
If you have a scanner, you can check to make sure that you've got the minimum air set correctly. Just start the truck, and take a look at the IAC counts being shown. At a full temp idle in drive, you should be at approx 600 rpm, and the IAC should be showing about 35 counts or so. Any higher, and you have your idle set too low, causing the IAC to open up too far to let more air in, and lower, and your idle is set too high, making the IAC close way up.
Sorry about the lack of paragraphs, and or any run on sentances, this was just kind poured outta my mind into the keyboard, lol
Take the IAC right out of the housing, and without forcing the needle to move, clean off the pintle, then the entire IAC housing of any and all carbon deposits from the PVC.
Put the IAC back in, then set minimum air. This is done by starting the truck, and letting it get to full operating temperature, then shutting the engine off and jumpering the two pins at the top right of the ALDL connector (white wire with a black stripe, and a black wire with a white stripe) turning the key to on, but not starting the truck, and waiting for at least 30 seconds to ensure that the IAC has the pintle all the way shut against the IAC housing. Once that is finished, unplug the IAC, pull the jumper out, and start the engine again, wait about 5 minutes for it to get back to full running temp if you took too long, punch out the little cap that protects the idle adjustment screw, then use a torx bit to back the idle off / advance it until it is at about 450 - 500 rpm or so in drive. (make sure to chalk the wheels, and set the parking brake before you get out of the vehicle with it in drive) Make sure that you don't set the idle up high enough for it to overcome the emergency brake, or the wheel chalks. Once you've got your minimum air set, go back inside the truck, turn it off, then go back to the front, plug the IAC back in, then turn the truck to ON again, without starting it, adjust the TPS so it is at about .54 volts at an idle, then unplug the negative battery terminal for approx 1 minute to reset any codes the ECM may have thrown with regards to the unplugged IAC. Start the truck back up, and without letting it idle for a while, take it for a 20 minute run. Make sure that the ECM experiences at least one second gear downshift, so it is able to use it's learning protocols across all the RPM vs MAP bands.
If you have a scanner, you can check to make sure that you've got the minimum air set correctly. Just start the truck, and take a look at the IAC counts being shown. At a full temp idle in drive, you should be at approx 600 rpm, and the IAC should be showing about 35 counts or so. Any higher, and you have your idle set too low, causing the IAC to open up too far to let more air in, and lower, and your idle is set too high, making the IAC close way up.
Sorry about the lack of paragraphs, and or any run on sentances, this was just kind poured outta my mind into the keyboard, lol
And wow, you are gonna be having a LOT of high idle troubles with that temp gauge that far off.
The temp gauge is located just to the passenger side of the thermostat housing, and will have a yellow and black wire going to it, check to make sure that it is plugged in, and if it is, get a new one. That temperature gauge should be reading the correct coolant temp pretty much to the degree.
The temp gauge is located just to the passenger side of the thermostat housing, and will have a yellow and black wire going to it, check to make sure that it is plugged in, and if it is, get a new one. That temperature gauge should be reading the correct coolant temp pretty much to the degree.
Russ i think the colant temp gauge works fine because we can get a reading before start up and after the engine warms up seams to be true.
The -40.0 dgree reading is in section #24 and labeled MANIFOLD AIR TMP.
Thanks for you help and I will have to read your post afew more times to get a handle on it.
The -40.0 dgree reading is in section #24 and labeled MANIFOLD AIR TMP.
Thanks for you help and I will have to read your post afew more times to get a handle on it.
Manifold Air Temp? Sorry, I missread your post, lol MAT is a car TBI / TPI thing, so there is a possiblity that your mechanic may have been right on with telling you to ignore that. If the scanner doesn't detect that at all, then it might just display some random value like -40.
To check and see if you have one, just look in the air box, the air ducting and the air cleaner. It'll have the same connector as the coolant temp sensor up front, infact, they are both the same sensor and are interchangeable.
Make sure that your coolant temp is accurate, along with the MAP and 02 sensors. Also check to make sure that your TPS is reading a smooth increase up to full voltage, not that it jumps in increments, or something like that.
I still personally think that your problem will probally be with minimum air not being set correctly, or becuase of a dirty IAC housing / pintle. If it was an EGR issue as suggested above, your truck would bog far longer than for a few seconds. When my EGR was messed up on the 89, it ran terrible all the time, and set a code when you were driving. Unplugging the EGR solenoid made the truck run real well all of a sudden, so that is a good way to checking the EGR off the list
To check and see if you have one, just look in the air box, the air ducting and the air cleaner. It'll have the same connector as the coolant temp sensor up front, infact, they are both the same sensor and are interchangeable.
Make sure that your coolant temp is accurate, along with the MAP and 02 sensors. Also check to make sure that your TPS is reading a smooth increase up to full voltage, not that it jumps in increments, or something like that.
I still personally think that your problem will probally be with minimum air not being set correctly, or becuase of a dirty IAC housing / pintle. If it was an EGR issue as suggested above, your truck would bog far longer than for a few seconds. When my EGR was messed up on the 89, it ran terrible all the time, and set a code when you were driving. Unplugging the EGR solenoid made the truck run real well all of a sudden, so that is a good way to checking the EGR off the list
I'd do my own research on the manifold air temp sensor.
Early truck TBI for sure did not have manifold air temp. I know that was a difference because I looked it up and the TBI cars DID use one.
I'd be somewhat surprised if trucks never went with one, but not astounded. Then again, with TBI cars gone at that point (to the best of my knowledge) there would be no reason to make a harness that has that connector and not use it.
-40* I believe indicates as low as can be indicated by the ECM, (infinite resistance) if you jump those two wires with the scanner on it temp should go to something like 304*.
Early truck TBI for sure did not have manifold air temp. I know that was a difference because I looked it up and the TBI cars DID use one.
I'd be somewhat surprised if trucks never went with one, but not astounded. Then again, with TBI cars gone at that point (to the best of my knowledge) there would be no reason to make a harness that has that connector and not use it.
-40* I believe indicates as low as can be indicated by the ECM, (infinite resistance) if you jump those two wires with the scanner on it temp should go to something like 304*.
