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OBD1 swapped D16Z6 ED2 manual Civic
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Discussion Starter #1
Hey all,

I have a really strange issue going on with my OBD1 Civic. When driving downhill, the CEL comes on, a few seconds later theres a pop from the exhaust and the CEL goes out again. While the CEL is on I can’t accelerate, the engine sounds like its suffocating. The moment the light goes off, the car is fine again. The CEL will continue to come on and off when going downhill until I’m on the flat again.

Its done this from the moment I swapped in the Z6 engine. I’ve tried pulling over to get the code, but the CEL has gone out and the ECU is appearing as if theres no codes, so it seems its clearing itself.

Some light reading has suggested it could be the distributor, mainly the igniter. However my tacho doesn’t bounce around as others have said.

Before I throw parts at it, does anyone have amy suggestions?

Thanks in advance!
 

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BATSLOMAN GIVES NO FUCKS.
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what is the fuel level when this happens?
 

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93 Civic HB SI
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I'd be curious what ignition and fuel are doing during this. Would need a scope to monitor secondary while driving, and injector pulse, but I'm curious if any of those critical things are dropping
 

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OBD1 swapped D16Z6 ED2 manual Civic
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Discussion Starter #6
I'd be curious what ignition and fuel are doing during this. Would need a scope to monitor secondary while driving, and injector pulse, but I'm curious if any of those critical things are dropping
That sounds like a definitive way of finding out, however its out of my ability.

Whatevers causing it is enough to trigger a CEL. I’m wondering if I can rig up the blue plug to a switch next to the steering wheel so I can try get the code while driving.
 

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93 Civic HB SI
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The CEL can come on for a number of reasons, some that don't mean there is a fault present.

Since your symptom is no throttle response when the CEL comes on, I'm curious as to what is causing the no throttle response, and what is triggering the no response.

It kinda sounds like the engine is briefly shutting off during the event, based on the way you describe the event, need to confirm this.

Engine needs fuel, air and ignition to run, and since the ECU is the gateway to providing the ignition and fuel part, need to verify if these are still present during the condition or not.

Is your car auto or manual? I'd be interested to see if you could get the condition to occur, then quickly shift to neutral and see if the engine dies immediately. You would know at that point the engine is losing what is needed to run during the condition. At that point, you'll need to start questioning what is being lost.
 

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next time it acts up, grab the ignition key and wiggle.
 
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OBD1 swapped D16Z6 ED2 manual Civic
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Discussion Starter #9
It kinda sounds like the engine is briefly shutting off during the event, based on the way you describe the event, need to confirm this.

Is your car auto or manual? I'd be interested to see if you could get the condition to occur, then quickly shift to neutral and see if the engine dies immediately. You would know at that point the engine is losing what is needed to run during the condition. At that point, you'll need to start questioning what is being lost.
Theres some good suggestions there. The cars a manual so shifting to neutral isnt a problem. Now you mention it, it does behave as if the engine is off during the condition. What I find strange is this only occurs downhill, which screams wiring fault to me. I’ll see if I can make it happen tomorrow on my way to work and test shifting to neutral to see what it does. Thank you!


next time it acts up, grab the ignition key and wiggle.
I hadn’t thought of that, could be as simple as bad ignition barrel wiring I guess!
 

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OBD1 swapped D16Z6 ED2 manual Civic
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Discussion Starter #11 (Edited)
It's those downhill wiring faults that always get ya :)
Seems that way yeah! So I tried shifting into neutral this morning and the engine stayed running, the revs dropped to 750 and that’s where they stayed.

Curiously, when the CEL went out, the revs dropped to about 400, then bounced up to 1200 before settling at 750 again. Any thoughts? Is this a maf/map issue perhaps? (I forget which).
 

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93 4d lx, z6,ported, port matched, compression bumped, balanced, manual swap
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Ive run into something similar one time, ended up being paint interfering with the ground on the thermostat housing with a bolt that was a bit rusty, it did the same things under decel, and over bumps.
 

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i have also seen similar issues with trash in fuel system gets moved around and clog filter or pump screen for a second and cause a no fuel issue.
 

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OBD1 swapped D16Z6 ED2 manual Civic
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Discussion Starter #14
Ive run into something similar one time, ended up being paint interfering with the ground on the thermostat housing with a bolt that was a bit rusty, it did the same things under decel, and over bumps.
That would make sense. I’ll go over all of the grounds and check the continuity between the ecu, thermostat housing and battery.


i have also seen similar issues with trash in fuel system gets moved around and clog filter or pump screen for a second and cause a no fuel issue.
My filter is only 300 miles old, but I’ll drain the fuel from it and see if its full of trash, just in case.
 

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OBD1 swapped D16Z6 ED2 manual Civic
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Discussion Starter #15
Ive run into something similar one time, ended up being paint interfering with the ground on the thermostat housing with a bolt that was a bit rusty, it did the same things under decel, and over bumps.
Fixed! Cleaning up the thermostat ground, and adding an extra engine ground has done the job. At least for now anyway. Thanks for the help!
 
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