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73-87 Chevy _ GMC Trucks => Fuel Systems and Drivability => Topic started by: buzzman351 on September 26, 2022, 05:40:51 am
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I have been replacing components lately and have seen the posts on how to check for codes but i have no check engine light. i actually reached up behind the cluster and it feels that where the CEL should be is just a plug. any ideas?
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The bulb socket may not have good electrical connections with the PCB, the bulb could be burned out or simply missing.
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theres a plug in its place like it didnt come with one and i was reading a diagnostic page and the instructions had (for trucks with CEL)
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What is the 'plug' that's in its place?
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the CEL light port where the bulb should be is capped off. i havent found a wire that would hook to a bulb. ive also seen write ups saying CEL is not present on some vehicles. that being said is there a digital scan tool that i can purchase to read diagnostics. trying to stay under 200 bucks
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or is there anywhere i can tap in with a test light to get the flashing codes?
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There is no 87 K10 so are you sure your truck is an 87? Is it TBI?
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Ok 87 V10. Yeah I’m sure
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But a scan tool recommendation would be greatly appreciated
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Post a pic of the instrument panel from the driver's seat and a pic of the "plug" that fills the CEL hole. Is there an ALDL connector mounted under the dash?
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I have changed out the MAP, TPS, IAC, EGR solenoid and valve, CTS. probably missing something but this is a TBI off of a 94. i had to splice in a TPS harness. the wire colors were the same so i figured it was all good. i can set base idle to about 750 and it will run at that idle for a bit. the next day it will go back to being around 1000. i performed the idle procedure that i found in the forum. ive sprayed throttle body cleaner around all hoses and gaskets. i even set timing again. any help?
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Have you looked for bad grounding wires?
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I did clean up the grounds that are by the thermostat. 2 of them. What others should I look for
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I've seen them on the firewall and passenger fender.
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I’ll check those as well
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Sounds like a vacuum leak.
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I honestly wouldn’t doubt it. Been correcting issues from the previous owner for a while. Would hvac vacuums effect it as well or are they separate
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Lord check out all these codes (https://uploads.tapatalk-cdn.com/20221018/4cb2ba7fd5418ff5ff5b9d86a79f247c.jpg)
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Many of those codes may be fictitious due to unplugging or activating sensors with the ignition ON during testing and swapping parts. You need to clear the trouble codes out of the ECM's memory and then determine which codes are active by seeing which reset during vehicle operation. Disconnect the battery ground cable for ~30 seconds then reconnect it and perform a vehicle road test - do not disconnect any sensors or wiring in the interim. Recheck for codes afterward.
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How long should I drive it and letting it run in the garage isn’t the same right
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Assuming it's road worthy, take it out and use it. Take a buzz down the highway and drive it normally. Run some needed errands around town. See if any codes return as a result. Just remember to write down any codes that occur along with the date that you retrieve them so that you have an organized record and history, before disconnecting the battery or pulling the ECM B fuse, which will erase the memory.
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Ok will do. I did unhook the battery and checked them right after. Still there. Will do what you said my next day off
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So I drove it around. Codes would never reset. I checked grounds again, pulled ecm and reseated prom. Resinstalled. Same 10 codes there. Should I try grounding the ecm somewhere other than the intake or what other suggestions do you have
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Have you verified your grounds at the intake and the back of the cylinder head? If you have then the next step is to do some pinpoint testing.
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ive verified the grounds that i know of and can see. with those 10 codes i imagine its 1 component causing this. i noticed my alternator gauge was a bit low. unhooked the positive and the truck shut off. old school shade tree mechanics have told me that means i need to change the alternator. so thats what ill be doing tomorrow. other than that im leaning towards my computer
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I replaced the alternator and checked codes a few times. Still the same 10 codes…I’m stumped. Anyone feel free to message me
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Code 51 indicates a prom problem. Diagnostics says to reseat prom and see if code returns. Make sure you clear codes after reseat of prom or any component disconnect. If code 51 comes back it says replace prom. If it still comes back replace ECM. This is from Mitchel Pro Demand.
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I’ve reseated it. Just found two terrible grounds beside the distributor. One of them had four wires connected into 1. Im not sure why but I cleaned it all up and it’s running a little better. Haven’t checked codes yet. Will soon
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When it’s running every now and then I’ll hear a little huff out of the exhaust too
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Is the gas old? If yes, they make treatments that suspend crud like water condensation.
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Nah it’s fresh. I filled up with 93. Idk. All those codes just give me a feeling the computer is faulty but it does run and drive but it’s just not right
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More considerations...
Keep in mind that every ground wire has at least two ends. Poor electrical connections can occur in the wiring harness attachments to the ECM as well as the engine and/or chassis attachments.
Before condemning the ECM, unplug and thoroughly wash the PC board (PCB) edge connector terminals with some CRC or DeoxIT D aerosol electrical contact cleaner to remove any accumulated dust and oxidation.
In addition, the harness connector terminals can actually deform or even break and lose contact tension against the PCB. Although tedious to perform, tension can be restored by gently reforming each terminal with a very fine point pick tool. But the learning curve is steep and calls for terminal-specific release tools, requiring excruciating care so as not to damage the small terminals and make circumstances worse. If necessary, many of the ECM-purposed terminals can be procured brand new from Mouser, Waytek, Digi-Key, et al and replaced if broken or damaged beyond use.
Lastly, the fine 22-gauge wires used to manufacture the ECM harnesses can break at or near their terminal attachments due to flexing or rough handling. At the very least, ground wire continuity should be verified using voltage drop tests and/or resistance measurements.
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So how hard would it be to replace the harness? I imagine pretty tough but I’m at a standstill. Also I can check continuity but I do that from the ecm connections to under the hood?
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http://forum.73-87chevytrucks.com/smforum/index.php?topic=39252.0
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So how hard would it be to replace the harness? I imagine pretty tough but I’m at a standstill. Also I can check continuity but I do that from the ecm connections to under the hood?
I think that replacing the ECM harness this early in the game is a panicked overreaction with no valid cause. Don't let the circumstances overwhelm you. Really, it's all just nuts and bolts. Perform some tests. Use the resources and guidance provided by VZ. He has astonishing experience and skill. And, yes, wire continuity is validated end-to-end; grounds are validated appliance-to-battery negative.
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You can also do a amp draw test from Battery + to the negative pins on your connectors.
JUST MAKE SURE THEY GO TO GROUND FIRST!! ;)
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But when i remove the ecm b fuse the truck will not start so that tells me something in the ecm is working. Maybe I’m getting a bs set of codes from a faulty aldl connection. I’m using a innova 3120 scanner
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ECM B also powers the fuel pump. Have you perused the library posted in our Technical Forum? Study the 1987 Light Duty Truck Fuel, Drivability and Emissions Manual (http://www.73-87chevytrucks.com/techinfo/7387CKMans//Fuel_Emissions/X8736_1987_GMC_Light_Duty_Truck_Fuel_and_Emissions_Including_Driveability.pdf).
Trouble codes are generated by the ECM for whatever their cause. I think faulty ALDL connections would more likely result in no scanner reading than false trouble code reporting.
You can also do a amp draw test from Battery + to the negative pins on your connectors.
JUST MAKE SURE THEY GO TO GROUND FIRST!! ;)
:o
Okay. The way that's been worded, "You can also do a amp draw test from Battery + to the negative pins on your connectors. JUST MAKE SURE THEY GO TO GROUND FIRST!!" will make the ammeter the circuit load, momentarily producing 4TH of July fireworks just before blowing the meter's internal fuse. I know that you know what you mean, so what am I missing? ???
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using my innova 3120 code reader on this truck. do you think maybe its showing me false codes bc its not reading correctly? also i cant do the check engine light code read out. there isnt a check engine light. im pretty sure there wasnt one from factory. there isnt a wire for CEL at the ALDL or on the harness
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B+
Load (light bulb)
Ammeter (digital)
Ground pin
Any significant variance would indicate a poor ground wire/pin/grounding point.
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Thanks for clarifying! ;)
That makes perfect sense, now. ;D 8)
Time for a nap...
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well if the ALDL is in fact giving me correct codes the 55 code says to replace ECM. that would probably explain the rest of the codes.
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but i was just reading on the link you posted BD and while running i was unplugging and wiggling a few things and i did uplug the electronic spark control module and nothing changed with the truck performance. my guess is that its bad
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The two ecm grounds from the ecm connector to the negative battery terminal have continuity a little over 5 ohms
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The ECM grounds for a SBC TBI engine are pins A12 and D1 (image).
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well with the help of a very knowledgeable resource I have been able to make a lot of headway. I found the ECM grounds and cleaned them extremely well, installed new terminals, crimped and soldered them and reinstalled. moved on to setting timing and base idle. truck still wanted to surge a bit. pulled TBI and inspected throttle shaft movement, and idle plates. all looked good. I was advised to cover or plug the IAC valve fresh air intake above the valve itself while setting base idle, which is to be 600 RPM in drive. I did this and buttoned everything up. truck is running much better now. i have found that I get a code 32 EGR and code 43 knock sensor from time to time. I plan on troubleshooting this as soon as my work schedule frees up a bit. I have a slight inclination that the EGR solenoid from amazon may be the culprit but we will see. I have the drivability manual on hand to refer to. I may be wrong but I believe the code 32 is causing the code 43. time will tell. Very good resources on this forum. As far as my service engine light I was advised which output from the ECM to probe with I+. it works at the ECM. I asked my resource to send me a link to the socket and bulb needed to fix this at the cluster. after looking at it I have no choice but to admit my mistake. The plug I thought i was feeling on the back of the cluster was the complete socket. I am a novice at this and I imagined there were supposed to be power wires coming from the plug. needless to say I removed the socket, installed a bulb and and all good. working SES. Learning has occured. Will update as i go further into the EGR issue.