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Hi all, noob here.
Long story short, my buddy gave me a 1995 Honda Civic EX manual transmission because his mechanic could not figure out his no start issue. Cranks but does not fire. Upon looking at it the first time, wouldn't even crank. Checked the starter, banged on it and it turned very slowly. My guess is they ruined the starter by cranking so much, probably continuously too. Anyhow, get a rebuilt starter, put it in and makes a horrible grinding noise. Find out the set screw from the distributor rotor came loose and screw was bouncing around hitting the contact points on the cap. Put a new cap and rotor, check spark, good to go.
Also, the PGM FI main relay is hanging on the drivers side and ECU is on the floor of the passenger floor. CEL stays on in the ignition on position.
I notice the fuel pump is not priming when turning the key on. I run power directly to the fuel pump, car finally fires after multiple cranks, take it for a spin, runs great and no CEL.
I check the main relay by the instructions in the manual by bench testing the relay with 12v and ground. Relay doesnt click, no continuity, etc etc. Get a new relay and bench test it the same way and everything works as it is suppose to. Relay clicks and continuity between the prongs that are suppose to have continuity. I install the relay and have good power (Yel/WHT) and ground (BLK and BLK/YEL) going into the relay. I turn the key on and have power (BLU/WHT)as well. I measure about 12.2 volts.
Here is the weird thing. I first probed the green/yellow wire with a test light that goes to the ECU and the fuel pump turns on with my probe light very dim. I measure voltage on the GRN/YEL wire and I only get 11.3 volts. I have continuity from that wire to the ECU at 0.2 to 0.3 ohms.
Using my probe light into the GRN/YEL wire is basically introducing ground into the circuit which tells me there is a bad ground somewhere. I checked the grounds at the thermostat and they all test good. I ended up cleaning them anyways.
My guess is there is a short in the ECU.
So I think to myself, I'll just keep the 12v wire to the fuel pump and drive the car around when I need to. Car doesn't start after multiple cranks. Leave it for an hour, come back and try to start it and finally starts. Drive it around some more, stop and start it a few times and seems fine. Come back this morning to try and start with the 12v direct to the fuel pump and now it won't start after sitting overnight.
Anybody have any tips or clues?
Thanks in advance. I felt bad just joining this forum to get help but I'm kind of at my wit's end. Hopefully I could return the favor here or on another forum.
I'm kind of in the same situation. My main relay doesn't engage unless I hot wire it. I've checked all grounds and fuses and power and nothing works. Got 3 new main relays and they all do the same. I've been trouble shooting for 4 days now and I'm really at a dead end. I do not mean to hijack this post, I just need help on the same situation. And I never commented or posted before cause I didn't think people were still active here until I saw your post date. But if any update on OPs answer or if anybody can help me, it's all appreciated
I don’t have another ecu to try unfortunately.
I did a little more reading and found out that the green/yellow from the ecu supplies ground to the relay which turns the pump on. The ecu ground is dependent on a crank position signal or rpm signal according to what i read. Also the ground will be supplied 2-3 seconds when first turning to on position to prime fuel system.
cranking the motor will also provide ground.
Without the crank or rpm signal the fuel pump would continue to run in the event of an accident.
I have some time tomorrow so I’ll try to check what I’ve read.
Can someone verify the crank and rpm signal is needed and which pins they are on the ecu? Also how to test them.
Sounds like you have done all the typically run thru. I am with you on making the assessment that the ECU may have a failed component. Fortunately, the OBD1 ECU's don't have micro electronic components so open the lid of the ECU and look for any burned out components (like resistors) or swollen/leaking caps.
Pin A7 is the fuel pump on the ECU. Here is a pinout of a P28...that should help you a lot.
I opened it up and it doesn't look that bad. No leaky capacitors or burned terminals. The microprocessor that the A7 fuel pump slot goes to looks normal.
So here is something interesting. I bypassed the ECU again by supplying ground to the GRN/Yel wire at the main relay. I had just charged the battery for 5 hours. The engine fired right up, no extended cranking. The higher voltage may have had something to do with the engine starting now. I tried this same exact thing 5 hours prior without a charged battery and the engine would not start. Just crank and crank and crank. I'm also getting 14.35 volts while the engine is running. I know anything over 14.5 is not good but 14.35 seems really high for a fully charged battery. Any thoughts?
Fuel pump read 11.8 volts. A little on the low side but it still powered up. So the car started today on the first few cranks. I'll have to try starting it cold again in the morning to see if it makes a difference. It looks as if the only wrong now is the ECU at the A7 pin not giving ground to the main relay to send power to fuel pump. I'll see what happens tomorrow.
It is normal to see voltage above 14.5 volts with our cars. I went on a wild electrical system goose chase before I came across this. Honda ELD Click and view PDF.
So here is something interesting. I bypassed the ECU again by supplying ground to the GRN/Yel wire at the main relay. I had just charged the battery for 5 hours. The engine fired right up, no extended cranking. The higher voltage may have had something to do with the engine starting now. I tried this same exact thing 5 hours prior without a charged battery and the engine would not start. Just crank and crank and crank. I'm also getting 14.35 volts while the engine is running. I know anything over 14.5 is not good but 14.35 seems really high for a fully charged battery. Any thoughts?
Both my K swap and B series have 14.3v at idle so i think your fine with the battery voltage.
I feel like this forum is more like I'm venting. Hahaha.
Anyways, car sat for 2 days and now it won't fire (start). Just cranks and cranks. The fuel pump is on and I do have spark. I'll have to check if my fuel pressure is good. Really strange why it runs fine when it starts but after sitting it just won't start anymore. I'll see what fuel pressure I have after I get a pressure gauge.
Thank you all for listening.
My 95 EX did this, after testing everything i could and replacing every component of the fuel system and ignition (needed to be done anyway) I’m almost certain it’s my p28. I’ve heard from others that these ECUs will have a no-prime issue. Sometimes it worked, sometimes it didn’t. Usually if the key is left in the ignition in the accessory position it would prime after a while.
Although by now Whazzup must have resolved this or given up, for future users "the PGM FI main relay is hanging on the drivers side" indicates that someone previously had a problem with that main relay module.
My '92 Civic DX had an intermittent relay: testing OK but sometimes no power to fuel pump until it was tapped or bumped, usually when starting but sometimes within a mile after starting. I even installed a permanent LED indicator to show when FP was powered, or needed a relay tap. Leaving the module hanging was a convenient way to do so.
Tapping on relays is a time-honored repair method for relay defects: both friction at the armature pivot and momentarily bad contacts (probably Ag/AgO for these relays).
But looking closely when that didn't work (installed relay testing "bad") revealed that the Mitsuba RZ-0132 module had a circuit board with a wide hole for the small relay coil pins, with a gap of about 1/16" to be bridged by soldering. That gap is no problem for wave-solder machines, but left a relatively heavy mass connected by solder over a relatively long distance, subject to vibration-induced fatigue failure in the solder. Looking with a 10X magnifier one saw a concentric hairline crack around some coil pins causing a high resistance. Easy to re-solder.
The relay's heavy contact and frame pins don't have this problem with more area for solder and less gap to the foil.
I never verified a too-high voltage on the grn/yel wire going to the ECU but a high resistance in that wire/driver could be a contributing or the primary factor as noted by others.
I note that the identical-looking "main" relay also in that module powers the ECU, so an intermittent by that relay could take out the injectors and spark also.
03-20-2022, 11:33 AM
95 Honda Civic Main Relay/ECU Fuel Pump issue
