73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: 1fishinrogers on April 11, 2011, 08:30:50 pm
-
I need some help straightening out a problem with the idle. It has a very rich gas exhaust and is loping but not all the time. It levels out and idles high occasionally but it doesn't last long. It also has tried to go dead in a pull a couple of times. It belonged to my dad and he never really took care of it from the day he brought it home 24 years ago so I started replacing most of the sensors: both oil pressure sensors, upper temp. sensor, idle air control, throttle position, new wires plugs dist. cap rotor button, ign. coil, vacuum hoses, set timing to factory setting, and rebuilt fuel reg. but haven't yet checked pump pressure. I also sprayed some cleaner in the mass air inlet port which helped at the time but didn't cure the loping but did stop it from going dead when it came down to idle. I unplugged the spark control mod. while it was idling and it didn't change anything, thought that was odd, maybe not? Any suggestions.
-
Sounds like the EGR is hanging open. This is usually caused by a sticking EGR solenoid or carbon in the EGR. Pull the vacuum hose off of the EGR valve and plug it. See if that makes any difference.
-
still doing the same thing, could it be control mod or a bad connection in the wiring?
-
Do you have any stored codes?
-
I do now the cil came on yesterday. Going to check it today and get back.
-
I went to check for codes but the cel doesn't come on when the switch is turned on but it does work because it was on the two days ago after it started missing. Can someone tell me where to start looking to find the problem with the check eng. light.
-
Have your key turned so the check engine light should be on,carefully move the wires behind the box.Mine was the same till I did this,hopefully the light will come on then.
-
CHART A-1 - NO "SERVICE ENGINE SOON" LIGHT
Circuit Description :
There should always be a steady "Service Engine Soon" light when the ignition is "ON" and engine stopped. Buttery ignition voltage is supplied to the light bulb. The ECM will control the light and turn it "ON" by providing a ground path through CKT 419.
Test Description : Numbers below refer to circled numbers on the diagnostic chart.
If the fuse in holder is blown, refer to facing page of Code 54 for complete circuit.
Using a test light connected to 12 volts, probe each of the system ground circuits to be sure a good ground is present. See ECM terminal end view in front of this section for ECM pin locations of ground circuits.
Diagnostic Aids :
If the engine runs 0K, check:
Faulty light bulb.
CKT 419 open.
Gage fuse blown. This will result in no stop lights, oil or generator lights, seat belt reminder, etc.
If the engine cranks but will not run, check:
Continuous battery-fuse or fusible link open.
ECM ignition fuse open.
Battery CKT 340 to ECM open.
Ignition CKT 439 to ECM open.
Poor connection to ECM.
-
Thanks, you were right on. Reached up behind cel and pushed on the harness and the light was on. Here are the codes, 12,22,32, 33 ,42, 44. A lot going on it looks like, mostly low voltage signals probably loose or bad connections like the cel. Any suggestions ?
-
Do you have an idea how long you did not have a check engine light?Some of those codes could be old and are not an issue still.You might need to disconnect your battery for a few minutes to clear the codes and then run the truck again to see what codes come back.
-
I did pull the ecm fuse this morning and cleared the codes. You're right some probably are old but I should know sometime tomorrow what codes are current. Thanks
-
I finally had time time to check the codes after clearing the old ones out. The only thing that came back so far is 22, throttle pos. sen. low signal at idle. I unplugged the connector and put some nolox on the terminals and also done the same to all the other sensor connectors. So far the idle problem has stopped and no other codes have appeared.
-
Noalox or penetrox etc is essentially for aluiminum. If you are getting a TPS DTC check the TPS. Do you have a digital volt meter?
-
sure do. what do you suggest?
-
Test the tps by backprobing it with a T-pin. Set your meter to the dc volts scale, key on engine off, backprobe cavity C of the TPS (grey wire) you should have approx 5 volts. Backprobe cavity B dark blue wire and with the throttle closed you should see approx .5V - now slowly open the throttle and the voltage should steadily increase with no glitches all the way to approx 4.5V If there are any glitches replace the TPS.
-
I got another code coming home from work last night, 32 . barometric pressure / map sensor circuit failure ? I did notice that the truck ran really good going to work ( 45 min. drive ) for about 30 min but I could tell something changed slightly, I had to push further on throttle to get to down shift for incline but didn't get cel. Coming home it ran slightly better until half way then got the light and weaker, not missing or anything just not near as responsive. I don't know if its something getting hot and breaking down or just coincidence ?
-
32 is EGR - Are you sure you got the right code? If it's MAP check the vacuum supply and do a pinpoint test at the sensor.
-
I see what you are talking about, my book says Barometric pres sensor or egr diagnostic switch, but it is a 32 code. What do you recommend.
-
Is the EGR system hooked up?
-
no
-
Would Noalox or penetrox work on the connections at the TPS or what would?The reason I ask is I have tested or replaced a lot of emissions items to solve a idle issue that I had.Now it is back to a degree my truck can run great one minute and have a surging idle the next.Also on an 87 with the TBI what should the idle be at when in park at normal temp?Thanks
-
The loping is most likely from a vacuum leak. If you check all the hoses and can't find anything check the intake manifold gasket and throttle body gasket. Thats what I'm doing now. The Nolox is probably not a recommendation by mechanics but I've used it for a good while and it does fine on automotive connections. I can't find the specs on the idle speed but it's probably between 750 and 850 rpms.
-
just checked the codes again and now have a 33 map sensor ?
-
If I had a vacuum leak would it not be doing it all the time not just once in awhile?Thanks
-
have you checked for codes and make sure the egr valve is working accordingly with acceleration it could have carbon or be sticking open at idle, also check the vent on the egr vacuum control solenoid, it has to be open to allow the egr valve to function quick enough to prevent vacuum drop.
-
What's the manifold vacuum drop to when it's acting up? If you have a meter and a vacuum pump (optional) you can easily test the map sensor.
-
Update, I just got back to working on my truck and have noticed that after clearing the same code over and over( 22 ) that a couple of things happen consistently, the engine runs fine, idles fine and changes gears up and down shifts perfectly for about 15 minutes then the same symptoms begin, code 22 starts down shifting from over drive to 3rd and back about 3 or 4 times then it doesn't want to down shift unless you press half way down and the idle speed increases to about 1000 rpm's it also idles very rich before and after. I am going to check manifold vac. asap and check signal voltage wire on tps back to the ecm for a break or bad connector but can anyone tell me if this is common to the ecm going bad or where else should I look.
-
Test the tps by backprobing it with a T-pin. Set your meter to the dc volts scale, key on engine off, backprobe cavity C of the TPS (grey wire) you should have approx 5 volts. Backprobe cavity B dark blue wire and with the throttle closed you should see approx .5V - now slowly open the throttle and the voltage should steadily increase with no glitches all the way to approx 4.5V If there are any glitches replace the TPS.
-
Thanks for all your help. I followed these instructions and got all correct readings but I was pretty sure that the problem was in this circuit. I took it one step further after following the other trouble shooting info you sent on checking the ecm and 419 circuit. I probed the signal voltage wire just before it goes into the ecm with the switch on and only had .01 volts, but I knew I had .62 coming through the tps so after closely checking the connector found that even though it look good, it had little to no connectivety with the tps. I have a new connector ordered and will follow up after install. Thanks again for all the info.