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90 CRX Si
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Discussion Starter #1 (Edited)
Ok, so I've been helping a friend chase down a random fuel cut issue for the last few months to no avail. We've tried everything from TPS, main relay (from my car), distributor, and today we tried another Hondata S300. Oddly enough the car will not kick a TPS code even when it's unplugged. After a couple miles, same issue, car dies as we're going down the road. This time with the borrowed S300 it at least kicked a code 16. We'd been thinking it was a TPS issue because it was just like decel fuel cut, and had been trying to narrow it down but we're getting good 5V reference, ground and TPS readout back to the ECU.

I'll post a log and screenshot it where the car cut off. It's seeing some odd MAP readings (Hondata 4 bar) when it died, but he was pedaling the throttle to see if it would do anything. It was showing up to 4psi positive pressure, which seems weird to me. The code 16 does point to another route we initially thought which was something in the injector circuit.

Rundown of the car: 1990 Honda CRX DX, Rywire OBD0 DPFI to OBD1 MPFI harness and ECU adapter, D15B VTEC with JRSC, Hondata 4bar MAP, RC 440cc high impedence injectors.

Here's the log and I'll screenshot it for those who can't pull it up. Skip to 1:45 to see where it starts (different from the screenshot, had to cut the log down to fit DSO size requriements)

 

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90 CRX Si
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Discussion Starter #2
I forgot to add he also changed the fuel pump from the 300k+ mile one to a new Walbro. When it does yesterday, we couldn't hear the pump prime like all walbro's do (loudly) but it cranked after we keyed on and off a couple times looking at the data log.
 

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Hows the fuel pressure, any issues with the regulator? Does it happen sporadically or only under load?

Code 16 - Fuel Injector

Possibly a faulty injector or bad wiring, or is the software actually cutting fuel from the ECU? Someone might be able to chime in a bit better but I would think cod 16 would only be thrown if there is a continuity issue with the fuel injector circuit somewhere...
 

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Meat Popsicle
91 CRX Si
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How full is the tank?

If it's like both of the walbro kits I've installed, it'll start sucking in air after it goes below 1/2-1/3 tank because the elbow fits too loosely onto the sock.

I remember you saying you didn't have this issue on your CRX but both of the legit Walbro pumps and install kits that I've used had this problem. When it does happen, I see fuel pressure fluttering on my gauge and the pump priming sound exhibits a sort of grinding sound.

I also had some distributor-related issues before where I'd rev to about 4K and would hit a brick wall, and a CEL would intermittently flash. This doesn't seem like what's occurring in this case but I just wanted to throw it out there.
 

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90 CRX Si
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Discussion Starter #5
Hows the fuel pressure, any issues with the regulator? Does it happen sporadically or only under load?

Code 16 - Fuel Injector

Possibly a faulty injector or bad wiring, or is the software actually cutting fuel from the ECU? Someone might be able to chime in a bit better but I would think cod 16 would only be thrown if there is a continuity issue with the fuel injector circuit somewhere...
Sporadically. When I first started trying to help, I borrowed the car and drove it 3 days before it would do it.

How full is the tank?

If it's like both of the walbro kits I've installed, it'll start sucking in air after it goes below 1/2-1/3 tank because the elbow fits too loosely onto the sock.

I remember you saying you didn't have this issue on your CRX but both of the legit Walbro pumps and install kits that I've used had this problem. When it does happen, I see fuel pressure fluttering on my gauge and the pump priming sound exhibits a sort of grinding sound.

I also had some distributor-related issues before where I'd rev to about 4K and would hit a brick wall, and a CEL would intermittently flash. This doesn't seem like what's occurring in this case but I just wanted to throw it out there.
Well his was doing it before the Walbro and after. I'm not sure about fuel levels to be honest.

He did let me know he tried a stock MAP sensor and hasn't had any issues in driving 30 miles so far, but it has gone away for periods of days at a time, so we'll see.

I found a link talking about the main relay and power for the injectors and pump. On the DX, it says the injectors feed off a wire that powers the pump so I was thinking it may be something there, BUT if the main relay wasn't clicking it would be on the pre-relay side and powering the pump ONLY when the starter is engaged.
 

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88 RT4WD wagon
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well ive got nothing! that's what the gold wagon did when i first got it. weak connection in the ignition switch would lose power over 5k. and no pump prime once it died but you would get that solid CEL.
 

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Discussion Starter #9
So far, it seems the MAP was the issue. He's driven it well over 100 miles now without any issue. I think he's going to try the Hondata MAP this weekend and see if it acts up again.
 

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Discussion Starter #10
Final update: MAP's definitely the culprit. Plugged it in and it started doing the same thing before he left the driveway. Never seen one fail so intermittently before, or cause a fuel cutoff issue.
 

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90 CRX Si
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Discussion Starter #12
It can if the return voltage is low enough to bring it into decel area of the map
I thought it had to reach that condition as well as under a certain TPS? I lowered the conditions to reach decel fueling to where it shouldn't have been able to go into it. Oh well, it's fixed and he really doesn't need a 4bar MAP for the JRSC.
 
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