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Old 08-31-2006, 01:38 PM   #1
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Coasting @ 55 in N or in 5th? Honda injector question...

I've heard [here, actually] that while coasting [no throttle] in gear, Honda injectors cut fuel if the RPM is above something like 1k (can't remember exact number) Anyway, does this rule apply to older pre-OBD Hondas, say, a 1985 CRX Si (first year of FI for a Civic/CRX). If so, then it's safe to say coasting in 5th gear is better FE wise than just shifting to Neutral and rolling @ speed around 600-750 RPM [once warmed up]. Keep in mind I usually shift to N on short grades then shift to 5th and drop the clutch when resuming uphill when traffic is either too congested or the coast is too short to benefit from a FAS [cut engine off and coast in N til I bump it] Advice/knowledge? Thanks, Mak
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Old 08-31-2006, 01:43 PM   #2
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The way to tell is if it's "engine braking," at least on the newer stuff. If I throw it into 5th at 1300 with no throttle though it'll still shoot fuel, but if you get it to engine brake it won't.

However, this is all with electronics. I suspect that the carbbed stuff doesn't have such a feature, but I can't say for sure. Mehbe Gary will chime in for us.
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Old 09-02-2006, 09:49 AM   #3
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Well, I've wondered the same thing...but wow, I thought the CRX was carbed for '84-'86. I thought '87 was the first F.I.
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Old 09-02-2006, 02:19 PM   #4
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The CRX HF and non HF versions were carbed in 84-87. The Si was introduced in 85 and it was MPFI.
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Old 09-02-2006, 07:14 PM   #5
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krousdb is correct. In '88+, when they went to the newer body style, all models were FI even HF. DX had dual-point FI and Si/HF had Multi-point FI. Anyone figure the answer to my question yet? It engine brakes if I'm going at a nice click and just left off the gas to go down hill, it gives the feeling of the car is holding me back vs. a smooth cruise like in neutral. Where is the orignal post of "honda injectors cut off above _k?" Mak
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Old 09-03-2006, 07:49 AM   #6
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I'll see if I can find an answer in my honda factory shop manual http://www.nbtsc.org/~ryland/1984CivicShopManual/
Yesterday I was reading my new book How To Get More miles Per Gallon, and it said something about carburated cars (altho it didn't name any) that have a solinoid that under in gear deceleration, it will close off the fuel suply to the engine, and I know that at least the carburated hondas have a funny solinoid that I never knew what it did befor, but it makes sence that it would do this, and that fuel injection would be the next step, but this is still speculation.
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Old 09-03-2006, 07:28 PM   #7
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I spent a bit of time today looking at all the books I could find on the topic, but '84 to '88 chilton's manual doesn't have a wiring diagram, and my hanes manual is on lone, however I did find a 73 to 77 civic manual that has a wiring diagram, it apears that all civics with non cvcc engines from 73 to 76 had fuel cut off solinoids that are hooked to a speed sensor (over 12mph) an oil presure switch, and a vaccum switch, meening that under high vaccum (engine braking) the carburator's fuel suply is turned off as long as you are over 12mph, and have oil presure, in 1977 the cvcc (more complecated carburator, as well as more complecated head) finely got the same solinoids to stop the flow of fuel.
From what I remember of rebuilding my 1984 cvcc engined civic hatch back, it also had a number of solinoids on the carburator, altho I can not find a wiring diagram to tell me what they hook up to.
I've also in my 1984 honda civic factory shop manual (altho it doesn't cover US modles... but canada and UK) a test for testing the PGM-FI fuel cut off system on deceleration, so it would only make sense to me that if Honda started doing a fuel cut off system for deceleration starting in 1973 (first year of the civic) and kept doing it on thru all the modles to the present day.
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Old 09-05-2006, 11:56 AM   #8
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All the civic's and alot of other cars have anti diesel solonoids that are hooked to the ignition switch, but there are 3 extra solonoids on the carburator in the wiring diagram (for 1973-1977) that hook to those other sensors, and if I remember right the later civic's have multiple solonoids as well, altho I can't conferm this because of my missing wiring diagram, but I don't see why they would have stoped doing this for a few years.
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