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Discussion Starter · #1 ·
i just recently put a jdmb20 in my 91 si.. and now it runs very poorly..with a high idle around 2500 and it is missing runs rough..and bogs out in lower rpm..it olmost seems like a fuel problem.. but i am running out of things to check and i was wondering if i could get some help or atleast some input... everything on the motor is new or has been replaced.. i have checked the timing..replaced the injectors.. plugs..distributor.. wires.. regulator..coolant sensor..CYL sensor.. EAVC..TDC/CRANk sensor... and the injector resistor checks out good.. so at this point i have no idea..
 

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any trouble codes? vacuum leak? plug wires on the wrong plugs? timing belt off a tooth? vacuum lines connected to the wrong places? vacuum check valves in backwards? low coolant? injector plug loose or off?

check for trouble codes first, then investigate the rest i named. and check all plugs to make sure they are fully seated and clipped securely. more than likely, one of the above is at fault or partially at fault if you arent getting any codes.

just remember, its usually something stupid and little, and easy to miss. so triple check everything. even the things you would never think it to be, like plug wires on wrong plugs.

get a timing gun and double check the timing again
 

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Discussion Starter · #3 ·
no i have all the plug wires in the right place... and the injectors are all secured to their conectors.... i also checked most of the vacuum hoses and compared them to my other intake...adn from what i can tell they alll look good.. i wish i could find a diagram of somekind.. but they are all connected in the right spots i think.. but it also doesnt have any trouble codes in it.. but all the ones it did i took care of before.. and it has plenty of coolant in it too
 

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still sounds like some form of vacuum leak to me. either a cracked line, disconnected line, line connected to the wrong place, TB gasket, plenum gasket, mani gasket, injector seals (the big ones that they sit in sealing them to the mani), EACV gasket, IACV gasket, etc etc

or maybe your egr is clogged up and sticking open or closed a bit? thats common
 

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Discussion Starter · #6 ·
yeah.. but from the looks of it all the lines are new and connected.. so i dunno i will check again tomorrow... and all of the gaskets are new.. but also the weird things about it is that all of the plugs escept the one in #3 clyinder are fowled out after you run the car for a bit.. that is what is starting to confuse me more.


and about the clogged egr.. yes it can cause bogging when the car is warmed up.
 

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about the egr, it can bog the car to the point where it will barely even run at all.

as for the plugs being fouled out, well heres a question, you say you have a 91 si with a b20a. so i assume it originally was a b21? did you use the b20a head or the b21 head? and which head gasket did you get for it? a b20 HG or b21 hg?

have you done a compression test?
 

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Discussion Starter · #8 ·
yes i originally had a b21a1.. but now i have a jdm b20..with the head from that motor.. and i didnt change the head gasket on the b20 either because it checks out fine
 

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well, the only things that could cause the plugs to foul is a blown HG, bad rings, or injectors dumping way too much fuel.

if the plugs arent firing, they could also foul that way, but if you're idling at 2500, theres no way you're missing some spark lol. thats an air/fuel/combustion problem; which is either a leaky gasket, bad rings, or getting way too much fuel or air from somewhere else. running lean (air leak) wouldnt foul plugs though, running rich would foul plugs, or oil would foul plugs
 

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Discussion Starter · #10 ·
do you think that the ECU from the b21 would have anything to do with the injectors dumping more fuel?/
 

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are you using your B21A1 intake mani or the JDM B20A mani?
 

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Discussion Starter · #12 ·
i am using the jdm b20 manifold... but all the sensors and injectors are switched over.
 

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i will assume that you have a non EGR mani. so do you have the JDM ECU? if not you may want to swap the B20A mani for your B21A1 mani. if you have addressed this issue in some way that you don't have to use the EGR i would like to know how you did it. i also have the B20A but am running the B21A1 mani.
 

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Discussion Starter · #14 ·
yeah i dont have the egr... and i am using the ECU from the b21.. not the jdm ECU... i have the egr hooked up.. but its not in the manifold. its just bolted in a different spot in the engine bay.. from all of the time i have ran the motor i havent gotten any trouble codes from running without an egr. i just wanted to try and do away without using the egr, since i dont need it. well so far atleast
 

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well then it sounds like your prob lies some where else. sounds like some sort of a vaccum leak. by the way what did you block off the EGR valve hole with? it may be leaking from there. maybe not at first but eventually if it wasn't blocked off properly.
 

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Discussion Starter · #16 ·
it was blocked off with some sealant and a cap.. so that shouldn be the problem.. it seems to me like its more of a fuel problem but i still dont know for sure.. i need to do some more system checks
 

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theres your problem right there. even if the egr valve is not connected to the intake mani, if it cant open and close freely according to how the ecu tells it to, the motor will run like crap. the ecu can sense when the egr is sticking open or closed, and compensates for it by letting more or less air in and dumping more or less fuel.

if you put sealant on the egr valve, then capped it off, chances are the sealant is causing the valve to stick. which is in turn doing the above.
 

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motoxxxman said:
if you put sealant on the egr valve, then capped it off, chances are the sealant is causing the valve to stick. which is in turn doing the above.
I'm pretty sure he is referring to the EGR bung on the EXH manifold being "capped off", not the valve itself. My impression is that he just has the EGR valve electronicaly connected and mounted to the firewall (or some other place).

Don' really think that there is a huge benefit to be gained there...other than the asthetic of a cleaner engine bay...may want to consider the install of your B21 intake mani and EGR back to stock just to eliminate that as a possible source of your issue...I don't really recall reading any success stories with trying to use the JDM intake/USDM ECU combo.

Cheers!
 

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cidgrad130 said:
I'm pretty sure he is referring to the EGR bung on the EXH manifold being "capped off", not the valve itself. My impression is that he just has the EGR valve electronicaly connected and mounted to the firewall (or some other place).

Don' really think that there is a huge benefit to be gained there...other than the asthetic of a cleaner engine bay...may want to consider the install of your B21 intake mani and EGR back to stock just to eliminate that as a possible source of your issue...I don't really recall reading any success stories with trying to use the JDM intake/USDM ECU combo.

Cheers!

i agree. replace the B20 mani with the B21 mani. then go to the auto store and buy 10ft of vacuum hoses. cut to length and replace all your hoses.(make sure they're all in the right places)
 

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I have the JDM B20a In my 90 SR (si in the US) and it has the B21 manifolds and it works ok (cept my leaky gasket on the intake side, grr..) but yeah it seems to work fine with my ecu...


-mike
 
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