Hi! So I'm getting a Code 43 on my 93 civic. I did a mini-me swap on it so I've got a D15B8 block with a D16Z6 Head and I'm using a P28 ecu.

Right after doing the swap I was getting code 41, which is for the O2 heater. This makes sense because I was still using the single wire O2 sensor the car originally had and the P28 expects a 4-wire. I also learned that the D15B8 uses 180cc fuel injectors, but the P28 is programmed for 240cc injectors. So I figured that I'd be running very lean and should probably get some new injectors.

So recently I did a conversion to use a 4-wire oxygen sensor. Cut up a junk engine harness so I got the plug as well as the wires with pins for the O2 sensor. Got it wired into the factory connectors and used a multimeter to check for continuity between the plug and ecu, as well as checking for voltage. Everything working great. Put a brand new Denso oxygen sensor in, and as expected code 41 is gone. Cool. At the same time I did the O2 sensor I also put in a brand new set of 240cc fuel injectors and a new fuel filter.

However with that work done, when I run the car for 15 minutes or so, I'm now getting this Code 43 engine light and the engine REALLY bogs down. Once it starts moving and the rpms get higher it will suddenly get power back and sort of run ok, but then bog down again and run terribly when I slow down. If I turn the engine off and then immediately back on it will "fix" the issue for about 5 minutes.

So I started going through the flowchart. Tested the fuel pressure, ~34 psi and then ~44 with the vacuum line for the fuel regulator unplugged. So right where it's supposed to be. New fuel filter so knew that it couldn't be clogged. New fuel injectors so not those. Double checked the wiring for the oxygen sensor and then tested the sensor itself. Everything looking good. Checked for leaks around the oxygen sensor and the exhaust manifold. Completely out of ideas, tried every suggestion I found in other threads about code 43 issues.

 

Fuel pump. https://honda-tech.com/forums/appear.../#post49034372

 

When you wired in the 4-wire oxygen sensor, did you make sure to keep the shielding for the signal wire separate from the wire itself? I've seen where people just crimp the shielding and conductor together, and that can cause issues, though I'm not sure Code 43 is the code you'd get.

 

I de-pinned the signal wire from the single wire plug and then pinned it into the 4-wire plug I sourced. Then ran the heater, power, and ground wires to where they're supposed to go, pins and all. Didn't do any cutting, splicing, or crimping. Looking at the wiring diagrams, the single wire harness has the same shielding around signal wire as the 4-wire, so that's why I decided not to mess with the one and just reuse the original in my car.


I checked the fuel pressure and it's right where it's supposed to be so I don't think it's an issue with the fuel pump, or a clog in the feed line or fuel filter. If I pinch the return line the rpms go back up and the engine smooths out, so I think it's the FPR. I drive the car for a while and it runs great but then if I'm stopped at a light for a couple minutes, that's when the CEL comes on and the engine bogs down. So my thinking is that when I go back to idle the FPR is getting stuck open and the fuel pressure drops. Planning on grabbing a FPR from the junkyard and seeing if that causes any change.

Does anyone know if the fuel pump/FPR is different between the Civic CX which uses 180cc injectors and other Civics that use 240cc? It would make sense that the CX would have a slightly lower flow rate or that the FPR would have a slightly weaker spring, but all the information I've found says that all SOHC D-series use 70 lph pumps (though I've also seen people say that all d series used 240 injectors so maybe folks aren't aware of the CX exceptions).

 

I think all the 92-95 FPR's keep static rail pressure at 43 psi and let the injectors do the metering, regardless of trim level. So I think your logic is correct - go grab an FPR and swap it out, then see what happens.

 

how to check your FPR: https://honda-tech.com/forums/honda-...lator-3041304/

the 92-95 civic Helm manual says nothing about differing values per model. 40-47psi with vacuum hose disconnected, 31-38 with it connected (at idle)

edit -- after searching for a few moments, the USDM CX and VX share the same part number for the injectors, the other models have a different part number. this also has been confirmed by flow testing, the USDM CX and VX have 190cc injectors, the others have 240cc. (including the CDM CX) -- from here --> https://honda-tech.com/forums/honda-...-stock-900145/

 

Alright so I swapped in another regulator and the issue is still persisting, except now I have a bunch of new CEL codes! Pulled the ECU fuse to clear the codes just in case they were old, but they came back right away. Codes are as follows:

Code 1 - Heated Oxygen Sensor A
Code 7 - Throttle Position Sensor
Code 14 - Idle Air Control Valve or Bad ECM
Code 41 - Heated Oxygen Sensor Heater
Code 43 - Fuel Supply System

So I'm kind of leaning towards the ECU being bad. I'm already on my third ECU so this is not a thrilling prospect, especially since I don't have a working spare to swap in and see if it fixes the problem. I believe that all of those components share a ground (Green/White wire) so I'm just spit-balling if it could be that they're not getting proper ground and/or if the engine harness is going bad? Manual shows that the Grn-Wht wire goes to "Service Conn" but I don't know where that is and can't find it in other diagrams. I've previously cleaned the ground by the thermostat housing, but it doesn't seem like the Grn-Wht wire goes to it.

 

With that many that have had a problem, at this point I'm concerned that there's a short that's blowing your ECUs. Kindof a nightmare scenario.

Service connector is under the blower motor to the right, above the ECU.

 

OH! The service connector is the thing I've been jumping to get the engine codes! Cool. So how do I go about looking for a short, and are they any typical circuits to start that would damage the ECU like this if they shorted?

 

Could be a bad ground, indeed. Really, you need to start working through the troubleshooting flow diagrams in the Helms manual, paired with the wiring diagrams. They haven't let me down. I know I can't really help further until you've done that. That said, what I will add is that replacing the FPR shouldn't cause all those codes(???). Nor does it involve any electrical. So, did you touch or jostle any wiring harnesses while you did the work? That's where I would start hunting for a problem with a bad ground or an open wire. Could be a clue. Or a red herring!!

 

Could be a bad ground causing the issue.

GRN/WHT is +5V, not a ground.

 

The Grn/Wht wire that goes to the O2 sensor isn't a ground?

I've got a Hayne's manual, been doing the diagnostic flowchart for code 43 in that. Is the Helm's manual better or are they about the same? I unplugged the #1 injector to get the wire out of the way while I was replacing the FPR.

 

Using the Helm's manual is like tasting a proper espresso after suffering with drip coffee your entire life. "What the **** was I doing", you'll ask yourself. Hey, you don't know what you don't know. Don't beat yourself up.

 

My bad - you are correct. For the o2 sensor, GRN/WHT is the sensor ground.

And yes, Helm is far far superior to Haynes.

 

So a new wrinkle to this issue. Sometimes when I'm driving, no CEL at the time, if I try to accelerate and open up the throttle all the way I get no response. RPM doesn't budge, speed doesn't go up, nothing, but suddenly that code 43 comes back and my engine bogs down. So I'm starting to suspect that my cat is clogged and that's what's causing the code and the poor engine performance. Anyone know of any other issues that could cause a code 43 and poor performance at WOT?

 

Yes. When the fuel pump can't keep up because it's intermittently faulty. Mine stalled out my car, then on restart worked fine.

I know you want to jump to possible conclusions but you'll just throw money at the problem without being systematic about troubleshooting. STOP IT. FOLLOW THE HELMS MANUAL TROUBLESHOOTING GUIDE.

 

I have been following troubleshooting guides, my first post lists all the tests I had done prior to posting on the forum. And as per your suggestion I got the Helm manual and tried to follow the code 43 flowchart, however if you have code 43 with performance issues the manual tells you to go to "Fuel Supply System Page 11-89", but 11-89 is for the air conditioning, so the manual kind of sucks. I do not jump to conclusions, and I don't throw money at problems. I test. Thoroughly, meticulously, repeatedly. I have tested the fuel pump multiple times. It has passed every time. I'm looking at the Cat because the symptoms fit, the cat is 30 years old, my car used to burn a lot of oil and produce large clouds of smoke until I replaced the pistons rings and valve seals, and with the changes I've made to the engine the car could be running rich which can clog a cat over time. All of this means that a clogged cat is a possibility and something worth testing.

However, my current line of thinking is the Throttle Position Sensor. It was one of the CEL codes I got and since I get no throttle response when I press the pedal to the floor it seems a likely candidate. If I hold the pedal to the floor for a couple seconds, my car will throw a code 43 and bog down. My thinking is that with the throttle wide open more air is being let in, but the possible faulty TPS isn't telling the ECU to send more fuel. So my engine runs lean for a couple second, the O2 sensor detects this, throws a code 43 and the ECU switches to it's backup TPS setting which leads to the bogging down, aka limp mode. Continuing with this thinking, if the TPS is sending higher voltage than it should be at idle (my idle rpms are higher than they should be) this could be causing the engine to run rich, which again the O2 sensor detects, throws a code, etc. I tested the Yel-Wht wire that goes to the TPS so I know it's get 5v power like it should be. I'm about to go test the other wires to see how the voltage changes as I open and close the throttle.