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Old 02-28-2013, 08:07 PM   #1
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Icon2 Voltage drop at injectors- HELP! :(

Hey honda-tech! Long time reader, first time writer.

I've searched for an answer to this question, but I have a very specific set of circumstances and problem, so I haven't found an answer yet. I do apologise if this question has already been answered.

The car: Eg civic w/ b16a1 obd0 (pr3 ecu)

Ok, THE QUESTION! What would cause the voltage to drop at the injector clip, from 9v~ to 3-4-5v when an earth is applied, but the injector DOESN'T operate?

I've tested the continuity of the 9v injector wire to the ecu, which is solid, plus all the wires to the resistor box, and took an ohm reading of the injector, 2-3 ohms from memory. I've checked power to the resistor box, spark, fuel (at the rail), and checked that it fires after using a starting spray. I also checked a few of the grounds to the ecu, but if someone knows all the ones relevant to the injectors, please post, I will check again!

The history of the problem; I removed the fuel rail etc to paint the inlet manifold, and due to a few wires not having a connector (the car is custom wired) I had to cut about 8 wires on the LH (outlet) side of the fuel rail. Since connecting everything back up, the car has crank-no start. I got spark, fuel in the rail, ground to the ecu, timing hasn't changed (the car was running before I cut the wires), etc etc.

If you can, please help. This is driving me nuts... :/
I'm sorry if I have garbled the post, I tried to be as clear as I could. Please don't flame

Thanks guys!! I totally owe HT, some of your posts have saved my ***
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Old 03-01-2013, 05:32 AM   #2
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Default Re: Voltage drop at injectors- HELP! :(

Have you probed the injector wires with test light while cranking? Also, How did you check for spark?

http://techauto.awardspace.com/ignition.html

This link has a ton of good information in it. Could be a distributor related issue.
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Old 03-01-2013, 07:23 AM   #3
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Default Re: Voltage drop at injectors- HELP! :(

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Originally Posted by b-seriesEG View Post
I had to cut about 8 wires on the LH (outlet) side of the fuel rail. Since connecting everything back up, the car has crank-no start.
I would start there. Re-check all your work, make sure the order is correct and the solder joints are good.

You painted your intake manifold as well?
I'm wondering could that be preventing anything from grounding?
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its prolly piece of rust that fell inside the rotor causing it to be cricket and make the car shake ..when stoping or ...or prolly motor over flooded with oil leaks
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Old 03-01-2013, 04:58 PM   #4
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Default Re: Voltage drop at injectors- HELP! :(

If you are not running an injector resistor, voltage at the injector power lead, [lead that is the same color at all four injector] should be 12.5V, [or the same as it is at the batt. +/- .2-3 volts, if not, ch4eck the PGM-FI Main Relays fuel injector output, voltage there should also be the same as batt. voltage, if not, replace the PGM-FI Main Relay or try the fix...
http://techauto.tripod.com/mainrelay.htm.

A voltage drop is normal when a load is applied, but not by 50% .

The injector will not operate at voltages that low, your already low at 9V, 5V is really low, making me think you have a connection problem, either into or out of the PGM-FI Main Relay and if voltage is low at the injectors it is most likely low at the heated O2 sensor, and IGP1 and IGP2 of the ECU/ECM. 94
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Old 03-02-2013, 04:17 PM   #5
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Default Re: Voltage drop at injectors- HELP! :(

Keith; nah I used a multimeter to check spark, I took the spark plug out and grounded it to the block, and cranked...
I'm familiar with that site, it explains things very well

Grog; I've checked all my connections a million times, but unfortunately they are ok
I don't think I took any grounds off (it got painted while still bolted on) but I will check it anyway

Hey Fcm I've read quite a few of your posts before...
I am running a resistor box, so I should be getting about 9v, right?
I'm keen to check that relay, but I have no idea where it is or what it looks like :/ what would it be directly connected to?

Re voltage drop, yeah I agree, especially when the injector still doesn't operate!
What is IGP 1 and 2?
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Old 03-03-2013, 08:22 AM   #6
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Default Re: Voltage drop at injectors- HELP! :(

http://www.tegger.com/hondafaq/mainrelay.html

IGP1&2 are 12V+ "signal" inputs to the ECU/ECM also supplied by the injector relay in the PGM-FI Main Relay.

You said you checked power at the resister box, what was the input power? 94
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Old 03-03-2013, 08:56 PM   #7
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Default Re: Voltage drop at injectors- HELP! :(

Oh ok... I can't find this elusive relay, is it possible that another relay of a different type has been used? Due to the custom nature of the car.. It used to have a carbie, now its got an injected engine... I know where the relay for the fuel pump is. Its still good lol

I got just over 9 volts at the resistor box..
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Old 03-03-2013, 11:13 PM   #8
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Default Re: Voltage drop at injectors- HELP! :(

So I did a little test... The voltage at the resistor box drops to zero when one injector is earthed. However the voltage at igp 1 and 2 stay the same (11.9 v) :/ is this a sign of a bad earth in the injection circuit? What other earths are there, aside from the four at A2, A4, A16 and A18? (cause those are all good :/ )
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Old 03-04-2013, 02:50 AM   #9
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Default Re: Voltage drop at injectors- HELP! :(

Resolution!!
I made a wiring mistake, coupled with a bad wire :/ pin A15 from the ecu goes to the resistor box, and supplies the current for the injectors to function. I mixed this up with another wire, and to top it off, the correct wire had quite a high resistance (thus didn't beep on the setting I had my multimeter on for testing continuity), so it had me stumped for a fair while. I found a fantastic diagram for the function of the injectors AND the ignition system, but I don't know how to post a picture...

Anyway, wiring mistake, my bad, but I learnt something in the process... And I'm a HT member now :D

still can't find that damn relay tho :/
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Old 03-04-2013, 06:13 AM   #10
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Default Re: Voltage drop at injectors- HELP! :(

Hmmmmm, what is the MM&Y of the car, what is the year of the engine, [what MM&Y of car did it come out of]? 94
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Old 03-04-2013, 02:51 PM   #11
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Default Re: Voltage drop at injectors- HELP! :(

Well the shell is 09/93 but all I know is that the engine came from a jdm 89-91 integra...
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