So a new Denso fuel pump and strainer,fuel pump ECU bypass and ran great, stopped and started at least a dozen times. Then I get in to start it cold and its spins great but wont start. I ran 12v wire from battery to fuel pump and it fires right up. I thought I was going direct from key switch?

 

So I went out to start pulling my ignition switch, and now Im getting 12v. to the fuel pump again.

 

It'd be easier to help if you can give us all of your wiring setup for the pump. If you are bypassing your pump ecu, you will want to run a relay (30amp) and not run it in parallel off of existing wiring. Fuel pumps eat electricity so my suggestion is to 1. Not bypass the ecu unless you need to bc of the pump not liking lower voltage or 2. Rewire the whole pump setup with a relay. You can get fuel pump wiring kits from jegs that will work.

 

Ordered new ignition switch, see ignition switch post.

 

So i installed new ig. sw., disregarding what the other parts of the key switch assembly are. When you install the new switch, you will have to use a small tool to release 2 wires that come from the small black box attached to the side of the key switch housing. It is difficult and care should be taken to pry the release clips of those 2 wires in the right direction. Car seems to be repaired fully again.

 

This is getting old, after the new ig. switch, the car ran great for 4 days. Then after I went into store came out and no power to the fuel pump, so I jumped from the battery to fuel pump bypass wires and fired right up. I read another guys post that a main EFI relay fixed some issues with his car so I bought one for $28.00, no luck. Apparently Im not getting 12v. from the battery to the fuel pump. New fuel pump. ig. switch and EFI relay. Anyone know if it could be the integration relay? No other problems.

 

Have you looked into ECU issues? I've had similar experiences countless times, and seen several other people report likewise, of having a fix work for a few days and then revert to previous behavior. There seems to be some sort of memory issue at play.

 

I assume your talking about the engine man. ECU and not the fuel pump ECU?

 

Correct (sorry I didn't clarify, being a fuel pump ECU topic), but I'm not 100% convinced that the engine ECU is the only source of memory with these cars. There seems to be another unknown component somewhere, but I have no idea what it would be.

 

Since my only problem is that the fuel pump is not getting 12v. and that I have bypassed the fuel pump ECU, the only other 2 components would be the ig. sw. and the main EFI relay. Unless Im missing something. I just read a post with the same issue on a google search that the guy said there was something loose in his kick panel fuse box. Going out to check that.

 

With key on I could not find a loose connection or tapping on a relay that would make the fuel pump come on. After I did the wiggeling around on the wiring, the next time i turned the key off and then on the fuel pump was running. I wanted to prove to myself that the EFI relay in the engine fuse box was in line with the fuel pump, so I pulled the relay and the pump stopped. Then I plugged it back in with the key still on and the pump would not run. The connectors to the relay look like new and no banging around on the fuse box will make the pump run again. This is with the new relay.

 

Happen to be looking on rockauto and they also list a fuel pump opening relay and a fuel pump inertia switch. I think these items are not on our cars.

 

I know this is a bit off topic, but I am so glad I never bought a 400..

Aside from my comments, have you double checked the pump grounds? And when you say you bypassed the FP ecu, did you run an entire new wire from the battery to the stock EFI relay then to the pump? Cause that seems like a lot of extra work vs. just the standard 12v mod. and soldering 2 wires together...or am I still on this trend of misreading posts?

Remedy that I would suggest. Rewire the entire fuel pump. Dedicated 12v direct from the battery, to a relay with a fuse, and a new dedicated ground. By pass the car entirely just for the fuel pump.

 

You make a good point of bypassing the cars orig. wiring, but since I have no other issues with the wiring or drivability other than the fuel pump, Id like to use the stock wiring. Your first ques. ,no I only did the ecu bypass, the car starts and runs better, until you pull up somewhere after a week and have no power to the fuel pump. As far as the pump ground, all I have to do is run a 12v. jumper to the fuel pump and it works perf. BTW I have my old fuel pump ECU unplugged from the other orig. small wires of the plug, I do not think it was bad.

 

Taking shots in the dark here... If sitting for several days causes the problem, maybe it's a weak battery and as it drains down, it triggers something to fail downstream?