When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
My cars fuel pump at times will not prime. The issue seems related to humid conditions.
The issue resolves itself after some time, and seems at its most frequent when its raining/humid out.
There is no check engine light that stays lit, the fuses related to fuel are good , and the main relay clicks, but sometimes you wont here the humm of the pump priming, which results in a no start.
I checked for power at the fuel pump harness, and it does show about 12-volts kick in momentarily to prime the pump when the key is put in the on position.
I changed the fuel pump out, but the issue will occasionally happen again despite no check engine light and main relay clicking.
I swapped the main relay for a spare I have that's been re-soldered and I've placed dialectric grease where the harness plugs into the main relay to minimize effects of humidity but the issue still happens occasionally regardless of which of the two main relays I use.
The ECU was recently (last 2 months) refurbished with new capacitors/etc.
I checked the ground at the thermostat and it seems fine.
Some things to consider:
I have a fuel pump kill switch
I have a factory/OEM alarm system
I own two main relays for troubleshooting purposes and neither are new.
The battery is fairly new ( less than a year old, shows 12v power).
I have yet to replace the spark plugs or cap and rotor, but the car starts up just fine so long as fuel pump primes.
The ECU runs off a moates ostrich 2, with a ribbon cable the exits the side of the ECU into the external moates ostrich 2 unit.
Car is a 98 civic EX with a B series swap.
I've searched this issue extensively on honda-tech but couldn't find any with similar issues to mine that were actually resolved.
Any help would be greatly appreciated.
If you need any additional details just let me know.
The problem you describe is generally a bad ECU. You can figure out if it is the culprit by swapping in a known good ECU. Do you have friends who can help?
The problem you describe is generally a bad ECU. You can figure out if it is the culprit by swapping in a known good ECU. Do you have friends who can help?
i ruled out the ecu only because I recently had it refurbished. But you're right, just ordered another ECU.
I used to own a spare ecu for troubleshooting purposes , just like I own two main relays, but that spare ecu went bad on me and I haven't replaced it.
Does anyone know if spraying silicone spray on the PCB would cause any issues for the ECU?
Guys who run off-road RC cars spray their PCB's with the stuff, often to keep moisture exposure to the PCB from impacting its operation.
The problem almost surely lies with a bad capacitor. Maybe the people who refurbished your ECU did not replace all capacitors or botched the job. I'd return it to them.
Alternatively, you can test installed capacitors with an ESR meter or desoldered/removed capacitors with a capacitance meter. Testing and replacing electrolytic capacitors is pretty easy.
The issue came back albeit a bit differently. Fortunately I had purchased a spare ECU that arrived prior to the issue returning.
Swapped the replacement ECU, and issue persisted.
The car sounds like it wants to start but doesn't.
It turns over, seems to bog and then shuts off. Giving it throttle as it attempts to start yields no difference.
After some time, it starts just fine, as if the problem never existed.
I went ahead and changed out the plugs, cap and rotor (plug wires are less than year old) after the car was able to start again on the old plugs, cap and rotor and noticed the plugs seemed burnt (probably from running lean due to no fuel?)
I've heard some folks tell me its the starter, but it seems to crank over when I turn the key, and I don't hear any grinding or anything from the starter.
So back to square one.
If anyone has any suggestions, please reply as swapping out he ECU did not resolve the issue.
The fuel pump priming has nothing to do with a cap and rotor.
If you have fuel pump problems then its a main relay problem.
I recently had this issue with my civic as its been sitting in my garage in high humidity the past couple years.
The fuel pump priming has nothing to do with a cap and rotor.
If you have fuel pump problems then its a main relay problem.
I recently had this issue with my civic as its been sitting in my garage in high humidity the past couple years.
That's what I suspect. I have two Main relays I use for troubleshooting purposes and the issue was present with both.
They are not new relays though, so if it happens again, and the fuel pump doesn't prime, I may just purchase a new aftermarket main relay to remove all doubt.
Both relays do click though, and the check engine light doesn't stay lit.
When the issue returned, I didn't have enough time to check for spark or fuel before the issue went away, all I was able to do was swap in a good ECU (which didn't solve the issue, so swapped back to original ECU).
That's what I suspect. I have two Main relays I use for troubleshooting purposes and the issue was present with both.
They are not new relays though, so if it happens again, and the fuel pump doesn't prime, I may just purchase a new aftermarket main relay to remove all doubt.
Both relays do click though, and the check engine light doesn't stay lit.
When the issue returned, I didn't have enough time to check for spark or fuel before the issue went away, all I was able to do was swap in a good ECU (which didn't solve the issue, so swapped back to original ECU).
My relay was clicking too... but the pump wasn't priming. I bought a new relay from ebay for $25.
The car starts right up now every time without issue.
The issue returned, and everything seemed fine (no check engine light on, main relay clicks etc) with the exception of fuel pump not priming.
I decided to activate and deactivate the factory alarm system via the key-fob (which has been acting odd in the last few months) and the fuel pump primed but the car was hard to start. Gave it a few moments and reinserted the key to the ON position, let the pump prime for a bit, and the car started up like normal.
I switched over my dash and dash frame to a 99-00 Civic and the factory radio needed for the 96-98 OEM alarm system wouldn't fit, so I had to remove the face of the radio, exposing the circuit board inside, in order to properly hide the radio behind the dash.
I'm going to try and disable the OEM alarm system altogether while I search for a replacement OEM radio that's in tact.
If the issue returns while the factory alarm is disabled, then that rules out the OEM factory alarm and leaves just the Main Relay as the possible issue.
If the issue returns while the factory alarm is disabled, then that rules out the OEM factory alarm and leaves just the Main Relay as the possible issue.
What troubleshooting warrants this^ conclusion? Seems like a huge leap, but I may have missed something.
What troubleshooting warrants this^ conclusion? Seems like a huge leap, but I may have missed something.
It's the only part that has not been replaced with professionally refurbished or new part. Both my relays were used pats from the Junkyard that seem to work fine.
There's no "guarantee" per say that the issue will be a bad main relay, but its my best guess if the issue persists with the OEM alarm removed, given I've checked/swapped nearly everything else it could be.
On the haynes/chilton manual, for no fuel prime issues, it does state to check the OEM alarm if so equipped, due to it having some sort of control over the fuel?
For the last few months, the alarm has been inconsistent in responding to key-fob presses , even with new batteries installed on Keyfob, and me literally inches from the the car. Keyfob tests fine on key-fob tester too.
Either way ill keep everyone posted. I feel we're getting close.
In addition, it's quite uncommon for the main relays of 6th generation Civics to fail. In contrast, the main relays of 4th and 5th generation Civics were problematic.
Originally Posted by oresama
Both relays do click though, and the check engine light doesn't stay lit.
This^ key information is entirely inconsistent with either a bad main relay or bad ECU.
Was the fuel pump circuit altered for the B-series swap?
In addition, it's quite uncommon for the main relays of 6th generation Civics to fail. In contrast, the main relays of 4th and 5th generation Civics were problematic.
This^ key information is entirely inconsistent with either a bad main relay or bad ECU.
Was the fuel pump circuit altered for the B-series swap?
Does the fuel pump currently fail to prime despite the CEL turning on and then off after 2 seconds?
Currently its working fine, but when the issue is present its just as you described: it fails to prime despite the CEL turning on and then off after 2 seconds.
Currently its working fine, but when the issue is present its just as you described: it fails to prime despite the CEL turning on and then off after 2 seconds.
Tests must be done when the problem is evident.
When the problem is evident:
1) Unplug the main relay (MR) and use a jumper wire to short pin 7 to pin 4 in the free MR connector.
Does the pump run?
2) Turn key to ON(II) and then use the jumper wire to short pin 5 to pin 4 in the free MR connector.
Does the pump run?
Will do. The fuel pump issue seems to happen like clockwork after he car sits over the weekend.
I'll perform these steps then and report back.
Before you check whether the fuel pump primes with the key, remove the rear seat to create quick access to the fuel pump connector.
If the problem is evident and the wire jump tests do NOT make the pump run, then leave one pair of main relay pins jumped while you check whether battery voltage reaches the fuel pump connector.
If battery voltage does NOT reach the fuel pump, then there's a wire open between the main relay and fuel pump (kill switch-related problem?) or poor pin contacts in a connector that the wire runs through.
If battery voltage DOES reach the fuel pump connector, then either the fuel pump is bad or the fuel pump ground wire or its connection to the chassis is bad.
.
Last edited by muellersfan; 07-13-2019 at 09:40 PM.
"....then there's a wire open between the main relay and fuel pump (kill switch-related problem?) or poor pin contacts in a connector that the wire runs through."
I will try checking here next? Or should I consider something else?
06-24-2019, 01:17 PM
Fuel Pump intermittent no Prime
Re: Fuel Pump intermittent no Prime
Re: Fuel Pump intermittent no Prime
