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Discussion Starter #1
Hello All. I have recently converted my 1990 Civic RT4WD with a rebuilt D16A6 to OBD1 with a Rywire Budget Harness, D15B7 Distributor, Fuel Injector Clinic 525cc High Impedance Injectors, and Hondata P28 ECU.

It is worth noting that I have the starter directly wired to a momentary switch (Push to Start).

I was able to flash a basemap for my build on the P28 and start the car up, bleed the coolant, and adjust ignition timing. I turned the car off, let it cool down. I've since started the car a handful of times, driving it around the block, even redlining it. It ran SO well and smooth. No drama, just smiles.

The other day, I hop in the car and start it up. It idles at around 1,500 rpm for 15-20 seconds, then the rpm jumps to about 2,000, misfires 2 or 3 times, and then dies. While it's misfiring, I can hear the main relay toggling. I thought to myself, "great, the main relay probably went out."

First, I checked my fuses. All my fuses (fuses on the passenger strut tower and below the driver footwell) are all good. All contacts/leads for each fuse is also clean (no corrosion.)

Using : Checking Main Relay, with pics!!! - Honda-Tech - Honda Forum Discussion
I've tested the main relay and the harness. The only issue I came across is:

  1. Main Harness to Main Relay ohm'd out to ~450ohms. I repinned this harness connector to a new ground to resolve this, leaving the old ground wire disconnected/floating. Pin 2 is now 0ohms to chassis ground.
  2. I attach the positive probe of the voltmeter to the BLUE/WHITE wire (pin 4) and the negative probe to the BLACK wire (pin 2). When I turn the ignition switch to the START position, I only see 0.761V on the multimeter, not ~10V. When the key is out and the ignition is IG0, there is still 0.662V on pin 4.
  • I then checked #2 (10A) fuse. This is OK. Visual and continuity check both pass. Even tried a new fuse.
  • I checked the fuse box pad to the main relay connection and this is OK, no corrosion or issues.
  • Output of ignition switch two Blue/White wires is 12.54V reference chassis ground with car in Run (IG2), but it shows 0.635V when the key is out.
  • I checked the wiring between the ignition switch (two Blue/White wires) and the fuse box fuse terminal and there is an open; failed continuity check.
    • I can jump pins 5 and 7 on the Main Harness and the Fuel Pump will prime when I turn the ignition to IG2 (run).
    • Even if I jump Pins 1&3 and 5&7, turn the Key to Engine Run (IG2), the car will not run.
    • I found another switched 12V source. When I use that to feed power to Main Relay Harness Pin 4, Main Relay STILL will not throw to prime Fuel Pump.
I pulled the fuse box and did continuity checks from Fuse 2 locations to other terminal leads on the back of the fuse box - all passed continuity checks. I thought for sure wiring in a new switched 12V sourced connection directly to the main relay Pin 4 would fix this problem, but the relay still doesn't trigger Fuel Pump to prime.

Battery is new and in good health.

Ground wire on the thermostat house is secure. There is continuity on this wire and the chassis ground plane.

MY NEXT ACTIONS
  • I am about to install a new ignition switch and ohm out/continuity check the harness from Ignition Switch to the fuse box next.
  • I can also turn the ignition to IG1 ACC state and see if I can connect my laptop to the ECU Hondata USB port… Maybe this will tell me if the entire ECU is bad, or not… Least if it doesn’t turn on, then I can trouble shoot that too.
  • With ignition on (IG2), I have 12v on all injector plug terminals. With ignition off (IG0), I have 0V on all injector plug terminals. This looks good. I have a NOID tester, so next step is to see if ECU is grounding signal to pulse. Even though I have fuel pressure and can prime/run the Fuel Pump, I don't believe the injectors are firing as I never smell any fuel in the exhaust... I postulate that the ECU is not grounding the injector pulses...

I will come back with an update. I wanted to go ahead and post this in hopes that someone can provide some trouble shooting insight here.

Thanks for any insight this community has to offer.
 

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Discussion Starter #3
As expected, new ignition switch did not change anything.

can plug my laptop into the Hondata, and I can see D2 LED blinking Red when connected. I have also have a Green LED at D4 in the top right corner that is permanently on. If I close Hondata S300 but leave the USB connected, the D2 red LED stops blinking and the Green LED at the D4 corner remains lit. I believe Hondata is working, but I noticed that I could not Upload a tune to Hondata; only download It didn't seem to matter if I was in KOEO, IG1, IG2, or key completely off. According to S300 Help (S300 Help), this could be a bad ECU socket...

I have 0.638V coming from the pair of Blue/White wires from the ignition switch when key is out, and 12.4v when the key is on run (IG2). I believe this is normal.

I will run some tests on the ECU Harness tomorrow. I will check to see if the voltages are right on the harness.

A23, A24, A26,B2, D21, D22 should all be grounded

A25 and B1 are 12V KOEO

D1 is 12V ALL the TIME

D19 and D20 are 5V KOEO.

I'll make these checks to ensure the harness is not bad.

All my chassis grounds are good. I'm leaning real close to a bad ECU...
 

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I know the guys on the Hondata support forum have been helpful with diagnosing issues with the ECU for me in the past. I'm sure they'll be able to give you some kind of advice given the detail in your posts.


My only advice would be to do a visual inspection of the board, and make sure there's no burnt areas or leaking capacitors. How did the test go for injector signal?
 

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Discussion Starter #5 (Edited)
Well... She's running again... All the voltages for the harness was exactly what they needed to be. I didn't change anything, but I think I know the problem.... But she's running again. Boy am I glad she's running again. One thing I noticed was the Hondata module wasn't seated all the way down when I started inspecting the ECU. It wasn't much, but probably enough that vibrations caused an intermittent connection that killed the fuel pump and injectors, followed by a no start fault. So much diagnosing. Word to others: check your fuses first, check your Hondata is seated if you've recently connected to it, then go about checking other stuff... It will save you a lot of time and effort. LOL...
137692


Some Hondata Bluetooth action while cruising the neighborhood.

137693
 

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Discussion Starter #6
I know the guys on the Hondata support forum have been helpful with diagnosing issues with the ECU for me in the past. I'm sure they'll be able to give you some kind of advice given the detail in your posts.


My only advice would be to do a visual inspection of the board, and make sure there's no burnt areas or leaking capacitors. How did the test go for injector signal?
Thanks for this suggestion. I haven't posted in the Hondata forums yet. I will make sure to keep this resource in mind in the future. Thank you for taking the time to post :)


make sure hondata is fully seated in the socket.
Thanks for this suggestion robgoof. I thought I had checked the socket was good when you suggested it, but all I did was make sure it was seated down. Yesterday, I actually pulled the Hondata board off, inspected it, and reseated it. Maybe it was that all along? World will never know... Driving the car as much as possible now to see if this was a fluke or if I have a real problem.
 

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Thanks for this suggestion. I haven't posted in the Hondata forums yet. I will make sure to keep this resource in mind in the future. Thank you for taking the time to post :)




Thanks for this suggestion robgoof. I thought I had checked the socket was good when you suggested it, but all I did was make sure it was seated down. Yesterday, I actually pulled the Hondata board off, inspected it, and reseated it. Maybe it was that all along? World will never know... Driving the car as much as possible now to see if this was a fluke or if I have a real problem.
hope it works out ,chasing gremlins is a pain.
 
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