Bad fuse box in a 99 Blazer?
Having problems with the gas pump and it has been replaced, the problem is that after stopping for example. to fill gasoline it will not start again and it does not help to connect power in the direct connection to the pump, and if we remove the relay then we still get signal on all 4 points when we try with a multimeter, that is not the pump there is something wrong with, the old one still works just as well. Do you also have a problem with one of the head lights, if we take out the fuse then there is power on both points of the fuse in the box, just as if it gets power from another location? It also happens several times that the 4x4 switch will not turn on, just flash, other times it works fine.
Do these cars use to get problems in the fuse boxes?

 

Are you having any other issues with your dash gauges? Temp gauge ect...

 

Yes, there was a time when the temperature gauge went all the way to the bottom when the engine was cold.

And when I measured the points in the fuse box to the relay for the petrol pump I had 12.43 volts on both 86 and 87 and there should be nothing at 87 whit no relay in place ?

 

Pin 87 on the relay is the normally open pin that gets connected to pin 30 which is the 'hot all times' +12V feed through fuse ECM B when the relay is energized. The wiring between the pump and the relay also has a circuit called the fuel pump prime circuit that is located right beside the FP relay in the underhood fuse box. The ECM should energize the relay for a short period of time after the ignition switch is placed into the run position to prime the system. If you always have power at the FP prime connection even without a relay in place, then there is a problem with the wiring in that somewhere on the circuit +12V has been directly connected.

Pin 86 on the relay shouldn't be power. That pin corresponds with the relay coil ground. Pin 85 is the +12V feed to the relay coil from the ECM fuel pump relay control pin (C4 pin 1 - dark green with white stripe wire).

After writing all of this, a thought occurred to me on the pin designations that invalidates the pin number to circuit functions I have detailed above. With the 4 pin relays used for the fuel pump and other systems on these trucks, pins 85 & 86 can be interchanged as can pins 30 & 87. The relays are not polarity dependent and they are symmetrical in that they can be placed into the socket in one of two different ways and work properly. So test for +12V on the fuel pump prime connector (location shown in the image below thanks to tjchevy59 in HIS REPLY in another thread - disregard the wiring diagram in the original post in that thread as it is not correct for the year vehicle being discussed there):

The prime connector is directly connected to the output of the relay, through there to the pump and not to the input or controls side of the relay.

If you have +12v on the prime connector for a short period after placing the key into the run position, I would then test for +12v at the pump connector along with a solid ground circuit.

While I cannot rule out an issue with the fuse box itself, I wouldn't jump to that conclusion off the bat. Many of the systems you have commented on can be on the complex side and simply pulling fuses and testing the pins in the fuse box does not give you the full picture of what's happening. I can only recommend that you fully inspect the wiring in each of the systems for modification and revert any modification back to a verified stock configuration prior to replacing parts or attempt to gain an understanding of why/how the modification was made. Electrical problems can be quite difficult to overcome and often require a significant amount of time reviewing the relevant wiring diagrams to understand what is going on in the circuit(s) involved. For this, I would recommend getting a factory service manual set or a subscription to an online service resource like AllDataDIY.com.

 

Thanks for the reply swartlkk.

Yes the electric can be very difficult to figure out unfortunately. If, however, I should change the fuse box, is it necessary to reprogram some things such as airbags, ecu etc?
There is also another thing that might have an impact on the electrical, sometimes we have to press the remote twice to the doors to turn off the security lamp.

 

No need to reprogram anything. You will have to get a box out of something that was similarly equipped to ensure that it has the proper circuits inside. I think there were two fuse box options, base & uplevel. Before you replace it, remove it and pull it apart but be aware that it isn't all that easy to get them opened up. There are lots of clips but overall they are very simple devices. Typically there is a top & bottom shell that houses layered steel sheets and plastic separator plates that make up the various traces from the connections at the bottom to the fuse/relay locations on the top. That is why I am doubtful that your box is the source of your problems as they are such simple things.

 

Thanks again swartlkk

 

Hi again.

As I mention above, sometimes we have to press twice on the remote control for the security lamp to turn off. Could this have anything to do with it starting as normal sometimes and sometimes not at all? Can eg. the ignition switch begin to wear so that the immobilizer switches on?