Nissan Forum banner
1 - 6 of 6 Posts

·
Registered
Joined
·
2,691 Posts
Was able to get the bed off and test it by the fuel pump and was getting about 40 fuel pressure before it dropped.
It's definitely a starvation problem if it runs on Brakleen, and if you're seeing pressure drop at the tank then chances are it's a tired or binding pump motor that's losing torque and speed when it gets warm. It won't be a blockage because you'd see rising pressure and not falling. I don't recall if D21's had a return-type regulator, if so it's possible that's causing a drop. You can check that easily by temporarily pinching off the return line to see if its disposition improves. Otherwise, just check voltage drop on the power and ground wiring to make sure that isn't the issue before condemning the pump. If your pump power is good then it sounds like a bad pump is the correct diagnosis.
 

·
Registered
Joined
·
2,691 Posts
I have yet to check the pressure at the injectors. I’ll definitely check that. Will do. I’ll definitely check those both. Yeah the pump cost a bit. Wanted to make sure before replacing it. Thanks so much for the reply.
The 40 psi at the tank is already way low. Normal is about 56 and I think factory minimum spec is 51. It won't be any higher at the engine, so there's little point in a downstream measurement.
 

·
Registered
Joined
·
2,691 Posts
The 60 psi with the return line pinched is healthy, and 40 with the return open looks to be normal for your old horse. The fact that the regulator return drives the pressure up means the flow is unobstructed in both directions. I doubt it's clogged injectors, because only running on Brakleen, it would have to be all of them. Injectors don't all clog at once unless there's sugar in the tank, and that clogs the pump and filter too.

I did find a bulletin, apparently there's a potential open-splice issue on '87~89 D21's. I can't find the bulletin itself, but here's the synopsis:

Vehicle:
1987 - 1989 Nissan D21 3.0
1987 - 1989 Nissan D21 2.4
Symptom: No start and no injector pulse.
System: Emissions/PCM/Fuel
Problem: No power to terminal 114 at the ECU.
Test & Fix: Terminal 114 is the battery feed to the computer. The wire is White/Red. Check for a splice problem in 2 possible locations. Check the splice under the hood in the harness about 8" from the Throttle Body Injection (TBI) connector going toward the passenger fender. Then check the splice located in the harness behind the passenger side kick panel. Repair as necessary.
Diagnostic Codes: N/A
 

·
Registered
Joined
·
2,691 Posts
I was able to test the injectors. Found out that they were not getting power. Then in the process of trying to test the issue there was one point which it got power but it was only 2v.
That bulletin was for no injector power. Power comes from the ECU on that model, and 2V on-and-off sounds exactly like high resistance in a splice. Not sure how you went about checking the wire, but it should show 12V from end to end.
 

·
Registered
Joined
·
2,691 Posts
Not short of (maybe) a scope. The injector drivers are N-channel transistors that are "open collector", meaning they can pull ground on the injector but they can't push any voltage. The trouble with that is, it's impossible to distinguish whether the transistor is blown or the ECM simply isn't firing it. Blown transistors will sometimes still pull a small amount of current and cause a telltale voltage fluctuation, but it will likely be so small that catching it with a VOM will be hopeless. Only a lab scope would show it up.
 

·
Registered
Joined
·
2,691 Posts
If the ECU is bad, it will actually throw that code.

I don't know how it knows when it is messed up, but it does.

The other option is like you said: manually check the pinouts to individual wires. The service manual has a procedure. Do you have the service manual?
It can detect an open wire or open injector, but not necessarily a bad drive transistor. It needs the transistor to work in order to see how much current is flowing, but a transistor that's blown through to the collector will look like current is flowing when it isn't. So internal driver failures often won't cause codes like a disconnection will.
 
1 - 6 of 6 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top