90 civic dual point FI problem

Anyone know how to troubleshoot a 90 1.5L with dual point fuel injection? Will only start and run with secondary fuel injector disconnected. Otherwise floods out and won't run. No trouble codes unless injector is
unplugged. Neither injector seems to leak only spray while engine is cranking. Tried all the tips in the Haynes book and all voltages and resistances seem OK for the injectors, MAP, temp sensor, air controller, etc. Any other ideas? Thanks
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Mike McDonald wrote:

secondary may be sticking open much longer than required. can you start the engine with secondary disconnected, then reconnect once running? if so, does it run ok or flood again? the secondary should not [or hardly] be injecting at idle, only on enrichment. if you can see it throwing fuel, with the engine warm at any rate, it's sticking open.
on a related matter, is the tandem valve opening ok? check it by disconnecting the tube on the diaphragm, opening the tandem valve [that's the "choke"-like thing at the top of the throttle body] and putting a wetted finger over the diaphragm inlet. the tandem valve should stay open. if it closes, the diaphragm's shot. that's uncommon. much more likely is that the vacuum tube from the actuator is leaking. simple & cheap to replace about 1.5".
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Thanks, Reconnecting the secondary does cause engine to reflood. I checked the injector out of car with a nine volt battery and it clicks OK. When in car, it does not leak when fuel line comes up to pressure, only when engine cranking or running, which makes me wonder if ECU is telling it to open. With other older FI systems I've worked on, the MAP sensor had the ability to stop the engine from starting or running by making the mixture go too rich. Would like to be able to verify MAP is OK or not to isolate problem to the injector. Voltages to the MAP connector OK, but there is no test given to test the MAP by itself. Don't get a trouble code for the MAP, but don't know if the ECU would set one or not. No reason to suspect the ECU is bad at this time, and they are usually the least likely to fail. Was wondering if there seemed to be a history of either a FI sensors going bad or injectors failing before I resort to replacing parts. Will check the tandam valve, mostly I'm holding that open manually to see down the barrel.

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Mike McDonald wrote:

that's good, but clicking != guaranteed correct function.

the best check is to get a scope & look at the signal. if it's the same as a functioning dpfi civic, it's not the ecu, but it's not likely to be the ecu anyway.

ecu will almost certainly set a code on the map sensor [or ap sensor in the passenger cabin] being defective.

if you hold the tandem open while you're running the engine, you'e going to have a problem - it works /with/ the auxillary injector to make sure there's sufficient vacuum to vaporize the fuel. no restriction from the tandem = no vacuum = "excess" fuel.
btw, what symptoms make you think it's flooding? if it's simply not starting, check the main relay. your vintage civic is a prime candidate for this very common problem.
otherwise, get yourself to a junk yard & get an auxillary injector. they rarely fail, so a used one is likely to work just fine - at least good enough to get a decent diagnostic.

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Thanks again. Will check out main relay, but since car will start when the plugs and throttle body are dry and secondary injector is disconnected, I doubt its bad. Could check signal to injector, but don't know what a proper one should look like. Simple DC check shows its not always on and in range. ~5 volts I think last time I checked. Voltage to air injector OK and its resistance OK also. If I don't come up with anything new, I guess I'll start with a new injector and see what happens. Hate to start replacing parts without knowing they're bad as it can get real expensive real fast.

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Mike McDonald wrote:

i sympathize, but you're caught between the rock & hard place of not having more extensive test equipment & not wanting to unnecessarily replace parts. if you don't have the gear, you got to replace parts. all you need is a used injector. it's not that expensive. poke about your local junk yard.

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