Fuel pump not priming fuel lines

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aasarsak

aasarsak

New Member
I have scoured the internet trying to find a solution to this problem, but I have not been able to find anything. Here is the situation.

Normally, when I turn the key on just before starting the car with the engine off (KOEO), the CEL comes on for 2 seconds. During the 2 seconds, I can hear the fuel pump priming the fuel lines. After the 2 seconds is up, the light goes off, and the fuel pump shuts off.

Ever since I installed my new ECU from xenocron.com, my car doesn't do that any more. I followed the troubleshooting steps outlined in the service manual, but I cannot identify the problem.

Most of the search results I got pointed to the main relay, so I took it out, hooked it up to the battery and checked for continuity between all the prescribed terminals as stated in the service manual. The relay appeared to be fine, but I decided to go ahead and replace it anyway. I replaced the main relay, same problem.

The next step, according to the service manual, is to check the main relay harness. I placed a jumper wire between the #5 and #7 terminals and switched the KOEO and viola! the CEL came on and the fuel pump started to humm quite well.

The only other possiblity I can come up with is that the ECU may not be sending the signal to the main relay to prime the fuel line because the car starts and runs extremely well.

Some things to consider. After I did the OBD1 conversion, I got a CEL code for ELD. I have no idea what that meant, so I replaced the ELD (the black box fuse holder thingy under the hood), but the CEL code for ELD did not go away even though I reset the ECU by disconnecting the negative battery cable. To keep this particular code from being indicated, I went into my engine management software (Neptune RTP) and disabled ELD.

The car runs fine except that during long freeway trips, the fuel will cut out. I know this is happening because my wideband 02 gauge indicates a sudden lean mixture and I can feel the loss of power. The wierd thing is that if I apply a little more throttle pressure, the car goes back over to rich and accelerates just fine. As soon as I resume constant throttle cruising, the fuel cuts out again.

I don't know if any of these issues are related, but that is basically what is going on. The fuel cutting out problem during cruise has been going on since before I did the OBD conversion.

I believe that the ECU is the problem, but I havent been able to find any source of information that explains how to tell if the ECU is sending the signal to prime the fuel lines.

Any suggestions?

Even though I think my particular setup is irrelevant to the problem since it seems to be a chassis problem, here it is anyway.

89 civic si (usdm)
P28 with Neptune RTP (tuned by Church Automotive: Long Beach, CA)
B16A
Walbro 255LPH fuel pump
Stock injectors
B&M FPR
DRAG T3/T04 turbo kit (FMU & MAP bypass removed)
Innovate LC-1 Wideband kit
 
"Ever since I installed my new ECU from xenocron.com," i would call them and see if this is normal for the ECU, looks like you've covered all the basics... unless you had a walbro before the swap, then you may have an issue there.
 
I talked to xenocron.com and they said that the fuel pump not priming is normal for the P28 with Neptune RTP, but what about the fuel cutting out while driving? And what about the ELD?

BTW, I'm sure the manufaturer designed the car to prime the fuel lines for a good reason. What are the potential negative effects of not priming the fuel line?
 
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The biggest problem you should see from a unprimed fuel system is an extended crank time. In extreme cases it could cause a no start.
 
Maybe I'll have to post another thread to try and get an answer for the fuel cutting out while driving. thanks all for your responses though.
 
aasarsak said:
Maybe I'll have to post another thread to try and get an answer for the fuel cutting out while driving. thanks all for your responses though.
Click to expand...

if you ever figure out the problem for this please let me know.. pm me or post it on here.. my b16a has been doing the same thing since i swapped it in..never had the problem with my d16a6 though
 
Thanks, lets me know I'm not alone. i have started another thread on here. You can search my posts and find it. It specifically asks about this problem
 
My instincts tell me it's either a bad fuel pump or a short somewhere because I have swapped ECUs already. Remember? I was running OBD 0 (PR3 ECU). Now that I'm running OBD 1 (P28 ECU), I'm still having the same problems, so it must be something unrelated to the ECU. I'm thinking that the problem is more than likely a short somewhere, but I don't know how to diagnose it because the problem only occurs while driving.
 
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I know it has been a long time, but my tuner helped me find the source of the problem. Turns out, the TPS setting in the ECU was off by a few volts. I went into Neptune and lowered it a little. Problem fixed. Turns out that the fuel was cutting out because I was applying too little throttle. Even though I was pressing the gas pedal, the ECU wasn't detecting any change in throttle position at low throttle pressure because the TPS wasn't dialed in correctly. Go figure... :doh:
So I went ahead and dialed it in properly so it actually reads 0% throttle when there is no pedal pressure, and 100% when the pedal is on the floor. Before, it was indicating about -2% when there was no pedal pressure which means that even when I was pressing the gas pedal, the ECU still thought that there was no pedal pressure.

Regarding the fuel pump not priming fuel lines, that is a standard security feature of the Neptune RTP device. No way to disable it unfortunately.
 
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