73-87chevytrucks.com
General Site Info => General Discussion => Topic started by: brlarl on May 04, 2007, 08:29:43 pm
-
I've got a question or two for anyone who may know!! This is not about a C10 but is about a 1985 CHEVY IROC-Z with TPI and VIN code "F"! The car was given to me and once I got it I tore down the engine as far as the taking the heads off and having them checked. They checked out fine no problems. I proceeded to replace the head gaskets setting them to torque specs and correct order, set the valves to proper setting by using the two revolution method first on #1 cylinder then one complete revolution to #6. I reinstalled the manifold using the correct torque and order of tightening the bolts. Distributor was stabbed right on the money with number one piston up in compression stroke. After getting it all back together I fired it up and after adjusting everything had the car running like a top!!! No misses no noises nothing what so ever, the car ran great!!!! After letting the car sit over night I went out the next morning to start the car and it ran like crap and still does!!. It idles real bad. The check engine light came on and set a "42" code. I pulled all the plugs and replaced them, replaced the ignition module, ignition coil, cleaned up all wires inside the distributor and checked for cracks. The only thing I did not change in the distributor was the pick up coil. I then proceeded to follow the steps in Alldata Pro listed for code "42". I checked the Resistance on wire 423 on the 4-wire connector of the distributor and it showed 800+ohms which shows to be an opened circuit on 423. Resistance should be 500ohms or less. I then checked all the wires as mentioned above and the reading went down to 498ohms but the car still runs the same. The car is missing, I also checked the routing of the plug wires, checked the fuel pressure (40-45 lbs key on), checked the engine compression ( highest being 165lbs-lowest being 150lbs). The problem has to be something simple but I can not figure it out. There were no other codes set just code "42". Help from anyone is greatly appreciated.
-
Brlarl, it sounds like trouble with the pickup coil or magnets. Does this copy of the codes help?
http://www.iroczone.com/specs/TroubleCodes.htm (http://www.iroczone.com/specs/TroubleCodes.htm)
-
Thanks for the info. I found the same info in all data. I may replace the pick up coil since everything else is new. Thanks again.
-
It's not the pick up coil. When you checked the resistance in ckt 423 to ground did you disconnect the ECM connectors and have the ignition switched on? Did you leave the EST connector in bypass when you originally set the timing? Did you set the timing?
-
Also make sure you reconnected those ground wires at the back of the cylinder head!
-
Yeah. Loose grounds are the cause of a lot of the elect. problems we see on here. Loose connectors too.
-
When I checked ckt 423 I did have the ignition on but did not disconnect the ECM. I did set the timing to 6 degrees BTDC. I did disconnect the bypass when doing so. I've checked and the vacuum hoses and made sure the grounds behind the drivers side head were reconnected tight. I'm stumped. If the ECM is bad what kind of problems would I have with the engine while it is running or would it even run at all? Thanks in advance! ???
-
Well if you didn't perform the steps in the diagnostic procedure correctly your results are invalid. You need to recheck it correctly.
-
What is the chance that the ECM is bad? I have not redone the test procedures for code "42" but lastnight I started the car and it ran fine!!! I ran as if I did not have any problems. How can the EMC be checked to see if indeed it is faulty? Thanks in advance.
-
Recheck all of your connections especially those I mentioned above. The only thing you can really do if it's a faulty ECM is lightly tap on it and see if anything happens. (do not beat it) I think you have a poor negative connection somewhere.
-
I checked all the grounds that I know of. Can you tell me where they are so that I can make sure that I'm looking in the right location. Or if there is a schematic I can look at please let me know. Thanks
-
If the car starts and runs ok it's got to have a good computer. I think the only way to make sure it's good is to r&r with another unit. Did you run the car long enough for a good warmup to make sure something wasn't breaking down when it warmed up?
BTW is the engine a 305 or 350?
-
Today after returning from work I went out to start the car and today it runs like .........well you know!!! I did not touch anything from yesterday as it was running great!!! Yes the car was at operating temp!! The car must have Gremlins?????
-
Well I think I have the problem figured out but can someone tell me what the purpose of the Burn Off Module "MAS" is? I've been able to Isolate the problem to this module. I got good deal on a reman. ECM with a Lifetime Warranty so I changed it out but there is this module attached to the ecm that has a small relay inside that if the contacts are opened the car dies out. I figure this is the problem since the car was running like crap after installing the new ECM and I tapped on the Smaller module and the car idled right?? Any suggestions from anyone? Thanks in advance.
-
Wha ju talkin bout willis?
(http://www.sitcomsonline.com/coleman85.jpg)
Post pix please because I have no idea what you're talking about
-
HAHAHAHAHA!!! Like the photo!! I will post the photos soon. Thanks
-
The smaller of the two is what is know as a Burn Off Module "MAS". I believe this is only on the 85 TPI motors in the IROC-Z? Thanks in advance.
-
Well with a 20 year old ECM that is subjected to vibration, moisture, heat and plain old age, solders on computer boards can get weak or wire leads on electronic components get corroded. If you tapped on it and it changed performance, replace that module with a known good unit.
-
The ECM HAS been changed. The smaller of the two is what I'm not too sure of. Heck I have never heard of a Burn Off Module, I need to know was it is and what it is for. Thanks for the input.
-
Here is the schematic from what I have been able to find on this small module?
-
LOL OK now I know what you're talkin bout! ;D
Burn off was for the MAF sensor- it's designed to burn off any cocky that gets on the maf sensor when you shut the car off. It's supposed to make the hot wire burn off anything - Let me see if I can find any detailed info on it for you.
-
CHART C-13, MAF BURN-OFF CHECK (5.0L)
Due to contaminates in the atmosphere a residue may build up on the air flow meters sensing wire. To maintain an accurate reading from the meter a "burn-off" cycle will only occur if the ignition is turned off while in the closed loop mode and this is determined by the sate of the serial data line (CKT 461). If the engine is shut down while in open loop or the ignition is cycled on to off, the serial data line will be in a high state (about 5 volts) and remain there for about 5 seconds. However, if the ignition is turned off while in closed loop the serial data line will go to about 2.5 volts for 5 seconds. This voltage (2.5 volts or less) is what triggers the control circuitry in the burn off module and causes burn-off to occur. When the conditions are met to activate burn-off, a 3 to 5 second delay will couur. After this delay the control circuitry will cause 12 volts to be applied on CKT 994 for 1 second and this will cause the meters sensing wire to glow red hot (about 1000°F) and the cycle is then complete.
A Code 33 or 34 will set if the airmeter fails and the same circuitry is used for MAF output as for burn off. Therefore the only functional check needed for the burn-off function is to check whether the burn-off signal is reaching the air meter after engine shutdown.
(http://i6.photobucket.com/albums/y228/Sabaka454/burnoff.gif)
In order for the burn-off cycle to function, the 12 volts on terminal E must remain until the burn-off signal occurs. This checks for the 12 volt shut down delay.
Grounding the ALCL terminal E causes the burn-off module to activate burnoff. This check will determine if the burn off module and wiring are OK.
(http://i6.photobucket.com/albums/y228/Sabaka454/burn.gif)
-
Sorry the image size restriction shrunk the flowchart and it's nearly impossible to read
-
Thanks for the info. Did you obtain the flow chart in AllData Pro? If so can you give me the path to find it so that I can read info? Thanks again!
-
One other question..........Can this module make the car run as if it has a real bad miss? I've checked and checked then double checked all the grounds and have not found any problems. After replacing the ECM and noticing this smaller module deals with the MAF I figure this may bee the problem. But again can this make the engine run like C#&P? Thanks Again.