Fuel injectors and rpm
08-09-2016, 09:22 PM
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Fuel injectors and rpm
I'm sitting here thinking about what else could be causing issues with my RX8 not wanting to start. I know its fuel related as it has spark and it has compression. Heres the question: I know the secondary injectors only come on after a certain rpm. Is that only under load? Or will they open at that rpm in park while revving the engine? Reason I ask is because I noticed that while my 8 hates to start, it will eventually start. Sometimes it runs smooth, other times it idles really rough. When it idles rough however, it will run smooth once I bring the rpm above roughly 3000 rpm. Could this be injectors?
08-09-2016, 10:51 PM
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I don't remember the exact numbers as the test was done months ago and I have since misplaced the paperwork, but I distinctly remember all faces being atleast 90psi, with none drastically different. Again, could be wrong, but I do know compression tested fine. Also, I'm fairly confident that its not a coolant leak as I have not lost coolant, and when I pull plugs (have 2 sets that alternate, I pull, spray with carb cleaner, and dry off) they are wet but smell heavily of gas, not coolant. Now, It did smoke very lightly when I first bought it. Cloud of blueish on start, and then very light blueish after, and the exhaust burned my eyes. Replaced the fuel pump, gutted the cat, and removed the muffler and the smoking is pretty much nonexistent, and the exhaust no longer burns my eyes. To be quite honest? When it runs fine there are no issues, but when its not running smooth, I will have hesitation on throttle, rough running below 3000 rpm, and occaisional stalling. And then sometimes itll act like one rotor isnt running for a second when I start it, but then start a few seconds later.
08-09-2016, 10:53 PM
#5
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Could be a low cranking RPM from a tired starter or battery as well as several other things.
Troubleshoot.
http://foxed.ca/rx7manual/2003mazdar..._S01_0016.html
Troubleshoot.
http://foxed.ca/rx7manual/2003mazdar..._S01_0016.html
Last edited by 9krpmrx8; 08-09-2016 at 10:55 PM.
08-09-2016, 11:03 PM
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Ive gone through the No.4 troubleshoot, and other than cleaning the SSV, and injectors, ive pretty much gone over everything. As for cranking rpm: on a fully charged battery, which in my case is an Optima RED35, sitting at 12.6v and 13.4 with jumper cables, the starter spins the engine at 275+ rpm. Now, let that voltage at the battery drop to 12.2 and 12.9 on cables and it barely makes 250 rpm. And I was mistaken. I just looked back through messages to a buddy of mine who was helping me with the 8, I was wrong. I guess I didnt have the results then either, but all rotor faces were at a minimum of 100 psi. Probably doesnt make a difference on failing engine or not, but figured I would correct myself. Really don't mind if the engine is going south. I just want to get it to start right now.
08-09-2016, 11:29 PM
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08-09-2016, 11:41 PM
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I highly doubt it's the injectors but sure a faulty P1 (all that are working at idle) could cause issues but failed injectors in an RX-8 is very, very rare. But if you have air, fuel, spark and 275RPM (no clue how you are measuring that) of cranking speed, then it is likely low compression.
But assuming will get you no where. Knowing the exact compression numbers would be needed because even 100 psi at 250RPM is an engine that is borderline failing so any other issues take a back seat.
But assuming will get you no where. Knowing the exact compression numbers would be needed because even 100 psi at 250RPM is an engine that is borderline failing so any other issues take a back seat.
Last edited by 9krpmrx8; 08-09-2016 at 11:48 PM.
08-09-2016, 11:47 PM
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I highly doubt it's the injectors but sure a faulty P1 could cause issues but failed injectors in an RX-8 is very, very rare. But if you have air, fuel, spark and 275RPM (no clue how you are measuring that) of cranking speed, then it is likely low compression.
But assuming will get you no where. Knowing the exact compression numbers would be needed.
But assuming will get you no where. Knowing the exact compression numbers would be needed.
Unless, you know, my LS2 coil swap is firing the plugs off wrong and still testing as if I have spark.
08-09-2016, 11:53 PM
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I'm using a scan tool to see cranking speed. And the reason I'm thinking it may be a fuel injector issue is because I don't know how long it sat begore I purchased it, or where/what type of fuel the previous owner used (bought it from a wrecker buddy who planned to figure it out but never had time). And with the crap gas we have here it is entirely possible that it sat long enough for the gas to gum up the injectors. Sure, I can send them off to be cleaned, tested, and balanced friday, but I can also do that at work with a 9v battery and carb cleaner.
Unless, you know, my LS2 coil swap is firing the plugs off wrong and still testing as if I have spark.
Unless, you know, my LS2 coil swap is firing the plugs off wrong and still testing as if I have spark.
08-09-2016, 11:58 PM
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I'm using a scan tool to see cranking speed. And the reason I'm thinking it may be a fuel injector issue is because I don't know how long it sat begore I purchased it, or where/what type of fuel the previous owner used (bought it from a wrecker buddy who planned to figure it out but never had time). And with the crap gas we have here it is entirely possible that it sat long enough for the gas to gum up the injectors. Sure, I can send them off to be cleaned, tested, and balanced friday, but I can also do that at work with a 9v battery and carb cleaner.
Unless, you know, my LS2 coil swap is firing the plugs off wrong and still testing as if I have spark.
Unless, you know, my LS2 coil swap is firing the plugs off wrong and still testing as if I have spark.
08-10-2016, 12:02 AM
#15
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Well that type of tester is not ideal but if you had a solid light at cranking then it's likely not the coils. But who knows, anything is possible with a cobbled together kit. But based on what you said, my guess is low compression. It has nothing to do with injectors.
08-10-2016, 12:03 AM
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Solid light? When cranking the light was blinking
08-10-2016, 12:08 AM
#17
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Well not really solid but fast and consistent. But an HEI tester is the best type of tester to use and only about $10.00. But again, this is all pretty meaningless with your compression numbers.
08-10-2016, 12:15 AM
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Humor me for a few and lets forget about compression for a couple minutes. Besides, if I rebuild/replace I'm gonna wanna make sure all this stuff is working 100% right? So humor me please. Say you suspected an issue with the primary injectors. Would you DIY clean them (carb cleaner and 9v), send them off to be serviced, or just replace? Keep in mind that there is a slight hesitation when giving it throttle at low rpm, but revving above 3000 there is no hesitation.
08-10-2016, 12:25 AM
#19
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You already know you have low compression, deal with that first and stop wasting your time chasing other non issues. Getting injectors cleaned and tested is cheap, I would never do it myself. New injectors are also a drop in the bucket.
08-10-2016, 12:28 AM
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I am fine with having low compression for right now. Once I sell the chevy 350 in my driveway I will rebuild the engine. Until then I want to eliminate any and all issues that could kill the rebuild. Hence why I ask so many questions about so many things. And you didnt really answer the question. Have the injectors serviced/flow tested/balanced for $25 each, or replace for $60 each?
Also, one of the reasons I'm thinking its not compression is because since I installed a new fuel pump, when it does finally decide to start, I can shut it off and it will restart hot within a few seconds. It was my understanding that low compression won't start that fast when hot.
Also, one of the reasons I'm thinking its not compression is because since I installed a new fuel pump, when it does finally decide to start, I can shut it off and it will restart hot within a few seconds. It was my understanding that low compression won't start that fast when hot.
08-10-2016, 11:56 PM
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You may be on to something with the o rings. Im assuming you are referring to the ones for the injectors. Cause when I pulled the injectors earlier so I can send them off for service on friday, the front primary lower o ring (the tall one that goes in the housing) stayed in the housing and when I fished it out with a pick it was rather oily/dirty compared to the rear injector.
08-22-2016, 08:35 PM
#22
You may be on to something with the o rings. Im assuming you are referring to the ones for the injectors. Cause when I pulled the injectors earlier so I can send them off for service on friday, the front primary lower o ring (the tall one that goes in the housing) stayed in the housing and when I fished it out with a pick it was rather oily/dirty compared to the rear injector.
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