i am trying to troubleshoot my wiring because i suspect something is shorting out. I dont know if an open circuit could blow the 20 amp fuse near the battery. If the maf power relay or the maf is unplugged, then i can run the car in limp home mode. I am so lost in this and i am looking for a direction to start in.

are there any people who can give me a tip?

There is a short finder tool coming in the mail, it makes a tone in the circuit that can be detected by a probe.

where do i begin and then what are the next logical steps to get to the short?

Third seperate maf. probably not the maf sensor itself

 

its taking forever to upload.

 

HERE ARE SOME MORE DIAGRAMS. I HAVE THE WHOLE BOOK WITH ME.

 

First off, an open will not blow a circuit. An open is just that, it's open. The best short or open tool there is, is an analog ohm meter or a digital multi meter with ohm readings. What are you suspecting is shorting out? The MAF? Is your ECM throwing any codes? There is also a trouble shooting section in the manual.

 

I don't know what I suspect is shorting out and blowing the fuse. PROBABLY SOMETHING RELATED TO THE CIRCUITS SPLICE POINTS AND GROUNDS THAT I OUTLINED IN THE DIAGRAMS?

That is why i am asking for something to start testing around. I can't get it started to see any codes because the 20 amp fuse keeps blowing when I place the ignition switch on.

I have looked and there is no procedure in the manual for this exact issue.

the gm manual does reccomend using the tool That I am ordering to find shorts to ground.

 

I'm sorry, you come here for help and the first thing you do is start with the capital letter B.S. You have given no information about your car, such as what year, what size engine, what model, what or when the problem started. So I'm assuming because of the manual, it's a 305 TPI. So are you blowing out the fuel pump fuse? Have you checked or replaced the fuel pump relay?

 

look here is my excuse about the all caps. I just bought a galaxy s8 and have not gotten used to the keyboard on it. It randomly just does that. Oops...

 

it is a 350 with an automatic transmission.
previous owner changed it from a 305 and it was in rough shape. I have replaced the fuel sender unit and pump, alternator, starter, water pump deleted the egr, and new injectors 22lb.
I just want a clean stock feel without the emissions horse **** on it.
but TPI is a pain in the butt.
is an 86 Iroc z.

The problem started suddenly after replacing a starter a little while ago.
I have replaced every relay. Ignition on and I can hear The fuel pump prime for a half second and then the fuse pops. However, we can rule that fuel pump circuit out because the fuse will not blow and the pump primes/gives perfect fuel pressure to run the car (in limp mode) when the maf sensor or power relay is disconnected from the harness like I already said. I have ohm'd out the fuel sender and the segment of harness leading to the sender. The fuel pump circuit is good.

 

If you know that I said in the first post that it can run With the maf power relay or maf disconnected, then why ask me if It's a faulty fuel pump relay?
How is engine size and transmission relevant to these circuits that the issue resides in?
the wiring for these circuits is identical between 305 and 350tpi.

Im not being a smart ***, I just want to be informed.

 

Since all relays are new and fuse 2 will not pop as long as the maf power relay or maf is disconnected from the harness, then the short must be downstream of the fuel relay and nearer to the maf and maf power relay side of the harness. I'm not going to throw any more parts at this until I have identified the short but the weather is so ****ing cold that I can't go outside to ohm any wires.

 

If you can get a look at the power distribution diagram, then you can see that the ecm Maf power, burn off, and fuel pump relays all are powered from inline fuse 2 (applicable on all tuned port injection thirdgens).

 

You are doing the right thing by referring to the svc. manuals. Keep up the effort, you will get it.

 

Thanks. I just found the power distribution diagram. I know what i need to test now, but cant because of the brutal weather here and no garage. I will upload some more images.

 

Here is some of the logic that I'm going to use plus the power distribution which shows that in line fuse #2 is not just a fuel fuse. Let me know if you have any suggestions besides changing relays. Done that.

 

How's the wiring look at the relays? Early thirdgens use some of the crappiest relays. It's not unusual for the relays to go bad and overheat the connectors, melt wiring, etc. Usually they're packed with grease to keep them from corroding, etc. It's fairly common for the insulation to shrink back away from the connector. Anything like that show up in the visual inspection phase?

Work through the issue, eliminate possibilities, it's NBD, just time consuming. Take your time, relax, and take things one step at a time.

 

I forgot to mention... The book most assuredly contains a convoluted, step-by-step process to troubleshooting your issue. Look for section 6E, go to the section that applies to your engine, and start on the first page. It'll say something like Driveability and Emissions. Look for where it says something like won't start, won't run. You might even read the section about checking the codes, and what to look for if the check engine light doesn't cooperate.

 

First this:

Then This:
Then this:


Your using diagrams from an 88 to diagnose an 86,..... not a good idea. Since the 88 wiring is different that the 86 you should really be using 86 diagrams just to be sure you're info is accurate.


IMO your description shows that the problem doesn't seem to be the #2 fuse at all, hat's just where it's showing up. That fuse should have battery power at all times. With the Key OFF and a good fuse in place,... does it blow or does it carry voltage to all the things it's connected to as it should ??

Power comes off the starter fusible link to fuse # 2. If the fuse doesn't blow when it's in place and the key is OFF then those circuits leading to the Fuse are OK. Power leaves the fuse and feeds the MAF relay, the ECM, The Fuel Pump, the FP switch, and the MAF Burn off relay.

This circuit does NOT feed the MAF,... but it does feed the MAF relay. Since when you unplug the MAF (means nothing) and unplug the MAF Relay ( BINGO !) and the fuse doesn't blow,........ check the MAF relay wiring carefully and or replace it (again !).

You can verify the other things powered by this circuit are OK if all things ( other than the MAF Relay ) are plugged in and the fuse doesn't blow when you turn the key. So; If you disconnect the MAF relay, turn the key, and the fuse still blows,... just unplug 1 more of the accessories at a time on that circuit and try again till you unplug the one that is making the fuse pop when the key is turned.

 

Oh Ya'.... Might want to check over your cooling fan relays too. The cooling fan relays get 'full time power' from the same fusible link that feeds in-line fuse #2. ( they also get "switched power" from the key and a fried relay could short the #2 fuse circuit. )

 

Thank you for the help. I was combing over all of my diagrams when I noticed the wiring colors for the Maf connector/pigtail. The pigtail was spliced into the harness in reverse order! Now I get to set the timing and redset the ecm. If I encounter any drivability issues from here on out, then I will post about it.

 

So I disconnected the spark control circuit above the passenger side strut and set timing to 6 degrees advance. Now the car throws no codes and idles around 6 to 7 hundred, I can maybe assume that the Maf is functioning at this point. When I try to accelerate past 2500 rpm the motor bogs down and stutters.

My next step will be to check my fuel pressure.
I'm ready to attack this when the weather warms a little bit