# Rpms dropping issue ( Most likely fuel pressure issue)



## Calebaa22 (May 5, 2021)

My truck is a manual Nissan d21 or hardbody. It’s a v6 se model. I was having a problem where my trucks rpms would drop and it would rev super low and almost die. It got to where I couldn’t even tap the gas to get the rpms up as it would kill it almost instantly. The only thing I could do was start it and be pressing the gas. Even if I took it out of gear it would try to die. I had to keep the rpms up for it to keep going. Now it’s to where it will not turn over. Was able to spray brake cleaner into the throttle body and that would keep it going. So I believe the issue is a fuel pressure problem. Was able to get the bed off and test it by the fuel pump and was getting about 40 fuel pressure before it dropped. I’ve researched it a bit but wanted to see if anyone knew anything about it. I’m thinking it might be a fuel pump that’s going out or a fuel pump sensor. Thanks so much for your time. If you have any questions let me know.


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## jp2code (Jun 2, 2011)

What is your fuel pressure at the injectors?


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## VStar650CL (Nov 12, 2020)

Calebaa22 said:


> 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.


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## Calebaa22 (May 5, 2021)

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.


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## VStar650CL (Nov 12, 2020)

Calebaa22 said:


> 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.


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## rogoman (Dec 16, 2004)

Calebaa22 said:


> 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.


Since you didn't specify the year of your D21, if it has the V6 engine , then it must be older then 1996. That being the case, it has a fuel pressure regulator at the fuel rail and a fuel filter in the engine compartment. Tee-in a temporary fuel pressure gauge between the fuel filter and the fuel rail. The readings at idle should be as follows:

with vacuum hose connected to the fuel pressure regulator: 34 psi
with vacuum hose disconnected from the fuel pressure regulator: 43 psi
If the pressure is out of spec, the pressure regulator may be bad or the fuel filter may be plugged up; they're OK, then the pump is marginal.


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## Calebaa22 (May 5, 2021)

Thanks for all the reply’s. It’s a 1989 d21. Did a couple checks on it and when I when I plugged the return line at the tank I actually had a rise in pressure to almost 60. And it was still losing pressure but this time it was a lot slower then when it wasn’t plugged. It’s making me think the problem is most likely the fuel pressure regulator. I replaced the fuel pump and even tested it with out the fuel filter and it was doing the same thing. It also will only start when I’m spraying brake cleaner into the throttle body and keep running if I keep spraying it. As soon as I stop it dies. I was researching them but I found that a lot of places had them discontinued or they were for a 90’s d21. Would a 90’s part work for this? I found the part numbers 22670-88G00 and 16240-03G15. Thanks a bunch for all the help.


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## jp2code (Jun 2, 2011)

Possible that you installed the fuel filter backwards


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## Calebaa22 (May 5, 2021)

Possibly. I’ve had the fuel filter in it for awhile. Got a new one on it now and it’s still the same. I also tried plugging the return line to check the pressure regulator but still nothing. I’m pretty positive it’s a fuel issue and it’s not getting to it. Could it possibly be the injectors not misting properly? I also put a new fuel pump on it.


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## Calebaa22 (May 5, 2021)

Oh and I completely forgot about it. I the check engine light on when I got it. Fixed it and got the check engine light off. But it had two codes reading even with the check engine light off. They were 23 and 45 which are idle switch and injector leak. My truck was running really good and the one who was helping me said it would be good. I’m thinking could this possibly be due to the injector leak. Weird thing is the check engine light still is not on. Could these effect it? Thanks a bunch


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## VStar650CL (Nov 12, 2020)

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


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## jp2code (Jun 2, 2011)

Calebaa22 said:


> Oh and I completely forgot about it. I the check engine light on when I got it. Fixed it and got the check engine light off. But it had two codes reading even with the check engine light off. They were 23 and 45 which are idle switch and injector leak. My truck was running really good and the one who was helping me said it would be good. I’m thinking could this possibly be due to the injector leak. Weird thing is the check engine light still is not on. Could these effect it? Thanks a bunch


The Check Engine Light CEL is reserved for Emissions issues. 

Bad injectors are common.


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## Calebaa22 (May 5, 2021)

Will do. I’ll definitely check these out. Thanks again for all the help


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## Calebaa22 (May 5, 2021)

I was able to check the wire and didn’t find any issues with it. But 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. I also check the power at the ecu for what I believe is the one going to the fuel pump and it was getting 12v there. Gonna check the line running to the ecu and the fuel pump again. Anyone know what might be the issue? Thanks a bunch for all the help.


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## VStar650CL (Nov 12, 2020)

Calebaa22 said:


> 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.


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## jp2code (Jun 2, 2011)

Calebaa22 said:


> I was able to check the wire and didn’t find any issues with it. But 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. I also check the power at the ecu for what I believe is the one going to the fuel pump and it was getting 12v there. Gonna check the line running to the ecu and the fuel pump again. Anyone know what might be the issue? Thanks a bunch for all the help.


Injectors do go out, so that is common.

The fusible links should protect electrical components like the injectors, but often they get bypassed when they burn out. Without the fusible links, you can easily burn up an injector whenever you try cranking your truck or someone else using jumper cables or if the alternator or voltage regulator is going out.

If you want to check on the state of your fusible links, here is info on it:






Fusible links - Infamous Nissan - Hardbody / Frontier Forums


Fusible links Hardbody Forum (D21)



www.infamousnissan.com


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## Oldcivicjoe (Jun 21, 2021)

So I got called in for backup on this one. And so far I've only been able to get intermittent injector pulse, but spark seems to be constant. At one point, while wiggling the crank angle sensor connector both injectors fired, since then nothing. 
I've checked continuity on both injector ground wires to the ecu, injectors now have a full 12 volts.
I'm suspecting the crank angle sensor or the pigtail from the bottom of the distributor to the engine harness.


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## jp2code (Jun 2, 2011)

Oldcivicjoe said:


> So I got called in for backup on this one. And so far I've only been able to get intermittent injector pulse, but spark seems to be constant. At one point, while wiggling the crank angle sensor connector both injectors fired, since then nothing.
> I've checked continuity on both injector ground wires to the ecu, injectors now have a full 12 volts.
> I'm suspecting the crank angle sensor or the pigtail from the bottom of the distributor to the engine harness.


The crank angle position sensor is in the distributor. When a distributor goes out, they cause all sorts of strange problems that are hard to diagnose. 

In other words, you might want to replace the distributor.


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## Oldcivicjoe (Jun 21, 2021)

Oh yeah, most likely the cause as the upper bearing blew out.


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## Calebaa22 (May 5, 2021)

Got some help from Joe and ended up getting the distributor replaced. It’s also getting the needed volts to the injectors it is just not grounding them. It started up when they were grounded manually. Seems like it’s most likely the ecu not grounding it as it should. Anyone know of a way to test it out? Or should I just try and pick up a new one? Thanks a bunch


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## VStar650CL (Nov 12, 2020)

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.


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## jp2code (Jun 2, 2011)

Calebaa22 said:


> Got some help from Joe and ended up getting the distributor replaced. It’s also getting the needed volts to the injectors it is just not grounding them. It started up when they were grounded manually. Seems like it’s most likely the ecu not grounding it as it should. Anyone know of a way to test it out? Or should I just try and pick up a new one? Thanks a bunch


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?


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## VStar650CL (Nov 12, 2020)

jp2code said:


> 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.


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## Calebaa22 (May 5, 2021)

Ended up getting the ecu. Then found out that the two injectors were only reading 1.3 and 1.5 ohms. Pretty sure it domino effected and messed up the injectors as well. Trying to get some remanufactured ones for it. Looked around but I couldn’t any with big sellers, only ones on like eBay. Want to be sure I get a working pair. Anyone know of a place I can pick up injectors or maybe send them in to get remanufactured. I saw a couple places that remanufactured them for the 2.4 and it was a lot cheaper option. Thanks for all the help. 1989 Nissan D21 3.0.


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## jp2code (Jun 2, 2011)

Calebaa22 said:


> Ended up getting the ecu. Then found out that the two injectors were only reading 1.3 and 1.5 ohms. Pretty sure it domino effected and messed up the injectors as well. Trying to get some remanufactured ones for it. Looked around but I couldn’t any with big sellers, only ones on like eBay. Want to be sure I get a working pair. Anyone know of a place I can pick up injectors or maybe send them in to get remanufactured. I saw a couple places that remanufactured them for the 2.4 4 cylinder and it was a lot cheaper option. Thanks for all the help. 1989 Nissan D21 3.0 v6.


You could try Rockauto.com Japanese manufacturers are good; Chinese are not.


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## Calebaa22 (May 5, 2021)

Yeah I had checked with them to send the injectors in and get them remanufactured but when I went to check out the option was gone. I’ll have to call them to see. Will do. Thanks a bunch


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## rogoman (Dec 16, 2004)

Calebaa22 said:


> Ended up getting the ecu. Then found out that the two injectors were only reading 1.3 and 1.5 ohms. Pretty sure it domino effected and messed up the injectors as well. Trying to get some remanufactured ones for it. Looked around but I couldn’t any with big sellers, only ones on like eBay. Want to be sure I get a working pair. Anyone know of a place I can pick up injectors or maybe send them in to get remanufactured. I saw a couple places that remanufactured them for the 2.4 and it was a lot cheaper option. Thanks for all the help. 1989 Nissan D21 3.0.


Check out GB Remanufacturing, Inc. I've used their service several times.


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## Oldcivicjoe (Jun 21, 2021)

So this one went down a rabbit hole on us, found so much fried stuff we arent sure which was the original failure, the upper dist bearing grenaded, injectors were shorted, then all the used ones We could find would just stick open after replacing dist and ecu to get the ecu to fire them. Parts being impossible to find for the tb injection We opted to convert to mpfi, just fired it up today, trying to get a video of the first key turn posted soon.😃


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## Oldcivicjoe (Jun 21, 2021)




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## jp2code (Jun 2, 2011)

Oldcivicjoe said:


> So this one went down a rabbit hole on us, found so much fried stuff we arent sure which was the original failure, the upper dist bearing grenaded, injectors were shorted, then all the used ones We could find would just stick open after replacing dist and ecu to get the ecu to fire them. Parts being impossible to find for the tb injection We opted to convert to mpfi, just fired it up today, trying to get a video of the first key turn posted soon.😃


Great job converting throttle body to MPI!

A little FYI on the MPI that I've learned if you do not put many miles on your old Hardbody: Do not use ethanol-mixed gasoline! After that stuff sits on the smaller MPI injectors, the o-rings start to dissolve and you'll be replacing them every 2 years or so. Get non-ethanol fuel only or drive it a lot.


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## Oldcivicjoe (Jun 21, 2021)

It will be a dd again after we finish buttoning it up, but its headed to a state where 0 e fuel can be had, so shouldn't be an issue. Thanks for the heads up.


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## domnickjerron (6 mo ago)

Calebaa22 said:


> My truck is a manual Nissan d21 or hardbody. It’s a v6 se model. I was having a problem where my trucks rpms would drop and it would rev super low and almost die. It got to where I couldn’t even tap the gas to get the rpms up as it would kill it almost instantly. The only thing I could do was start it and be pressing the gas. Even if I took it out of gear it would try to die. I had to keep the rpms up for it to keep going. Now it’s to where it will not turn over. Was able to spray brake cleaner into the throttle body and that would keep it going. So I believe the issue is a fuel pressure problem. Was able to get the bed off and test it by the fuel pump and was getting about 40 fuel pressure before it dropped. I’ve researched it a bit but wanted to see if anyone knew anything about it. I’m thinking it might be a fuel pump that’s going out or a fuel pump sensor. Thanks so much for your time. If you have any questions let me know.


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.
Speed Test​


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## jp2code (Jun 2, 2011)

For the 1989 Nissan D21 Hardbody, the fuel pressure should be about 36.3 psi, as indicated in the service manual.


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## Oldcivicjoe (Jun 21, 2021)

domnickjerron said:


> 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.
> Speed Test​


This issue was figured out a good while back, it was a cascade failure that I think started with a grenaded upper distributor bearing, ended up shorting out the ecu and then the injectors, a couple of relays, and the fusible link that powered the injectors. Upon trying to source the tbi injectors at the start of the covid lock down we found no one wants to rebuild them any more, so it's now been converted to mpfi off a 95 pathy and runs excellent, the ac has been rebuilt, new heater core, ect, ect. Other than the tach signal to gauge cluster dropping out randomly and needing to convert to electronic speedo and trans mounted vss(unless the one on the mechanical speedo will work to send that signal to the ecu, its jut not for some reason) everything works. I've got a few more weeks of tinkering before it moves off to a whole new state, so hopefully I'll have those last couple issues sorted, and be able go help a bit with cosmetic stuff before then.


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