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Quite Concerning
RX7 Community,
I got this RX-7 from a friend who bought it from a friend that used it for autocross and his daily driver. That being said I'm trying to look at this now reoccurring issue objectively, but I'm a bit lost with this ?transmission? issue. The stalling issue, I believe, is the carburetor asking to be rebuilt. The jolting in 3rd and 4th has got me sweating a bit. It seemed like the issue went away as the engine oil got to operating temperature (~182°F), but this information may not be related. Trouble in 3rd and 4th gear: Conditions: Outside Temp >54°F Speed 30-45mph RPM ~3,000 - jolting with rpms seemingly steady Stalling: - Sudden loss of power (@ ~4,000rpm) resulting in engine stall - Upon initial acceleration, there is a drop in rpm then it shoots up to the rpm I'm asking for Any and all help would be appreciated, ~TM68 |
Search Throttle Position Sensor
Pretty common cause for what you're describing and easy to adjust. Avoid the inclination to start screwing with stuff until you get a few opinions. Also, more info on your car would help; year, model, options, and pics! Welcome aboard,
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Additional Details
I hadn't thought about that. Thank you for the suggestion. I'll look into replacing the TPS.
You're right! Here is that additional info: 1983 Mazda Rx-7 GS w/ 102,600m. Relevant MODS: Larger Radiator, Oil Cooler, Holley Fuel Pump 7psi, & Cold Air Intake. https://cimg4.ibsrv.net/gimg/www.rx7...313eda7709.jpg https://cimg2.ibsrv.net/gimg/www.rx7...8484ec2132.jpg You can somewhat see a black box underneath the upper radiator hose. I believe it is for the aftermarket gauges inside the vehicle. Perhaps it is some sort of power managing system? https://cimg0.ibsrv.net/gimg/www.rx7...92f830f5e7.jpg https://cimg8.ibsrv.net/gimg/www.rx7...a2df324c20.jpg in line Fuel Filter is there https://cimg7.ibsrv.net/gimg/www.rx7...8b9f5aeb08.jpg You can kind of see the oversized radiator and the more powerful alternator is there too. https://cimg4.ibsrv.net/gimg/www.rx7...3e706d5a82.jpg Cold Air Intake, oil cooler https://cimg3.ibsrv.net/gimg/www.rx7...45e6311f8b.jpg |
Check adjustment of current TPS before replacing it.
Being that you have a Nikki carb on engine,unless you have a pressure regulator installed and adjusted,the 7psi from pump is too high for a Nikki carb. They need no higher than 2.5 psi to run properly. Higher fuel pressure can cause flooding,driveability issues. |
I'm trying to find more information on TPS. Is this a mechanical or electrical component of the Carburetor? x_X
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It’s an electrical tracking switch that sends a voltage signal to ecu to let it know where the throttle is from idle speed to wot and everything in between.
If you haven’t done so already go to foxedca.rx7manuals to read up on what is necessary to adjust TPS and how to do it. |
There's a lot of weird shit under your hood. The oil cooler w/fan is interesting. The large plastic jug/reservoir on the passenger side, closest to the carb... is that a premix tank, plumbed down to the OMP? I've been thinking about a setup like that.
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That is a premix tank
Originally Posted by Maxwedge
(Post 12373352)
There's a lot of weird shit under your hood. The oil cooler w/fan is interesting. The large plastic jug/reservoir on the passenger side, closest to the carb... is that a premix tank, plumbed down to the OMP? I've been thinking about a setup like that.
The battery was relocated to the trunk to make room for the oil cooler. There is a catch 22 with the oil cooler... Upon starting it keeps the oil temp cool for a long time xD Hasn't driven well these cold mornings when I've needed to travel in the 60mph range to work. It takes nearly a half-hour to get oil temp to reach 180°F. Also, it annoyingly runs above the dipstick and gets in the way of the oil filler tube. Though this set-up is good for autocross, daily driving is a different story. I want to upgrade the body and interior after the engine gets figured out. I still need to check on this TPS and fuel delivery issue. |
As indicated by GSLSEforme, foxed.ca has the factory service manual available on line for download. Here are a couple of screenshots of the TPS adjustment procedure taken from the 1985 FSM for reference.
https://cimg4.ibsrv.net/gimg/www.rx7...eff50d1a6.jpeg https://cimg3.ibsrv.net/gimg/www.rx7...61a367981.jpeg |
A second for whether there's a fpr. Looking at the photos I couldn't see one, but perhaps it's under that mass of hoses in the center. Since it idles and drives I would guess there is; just something to check.
The 4k stall sounds like - maybe - a somehow failing secondary side. As in, perhaps they're opening but no fuel is getting to them - I assume they're still vac. Not sure what condition the car was in before, but it could be a possibility? Does the stall happen at exactly 4k (or some other specific rpm) or is it more so load dependant and around 4k? Will it stall in the driveway (not moving) at the same rpm? Does it catch itself after stalling? The drop in rpm upon initial acceleration is probably a messed up AP, then the primaries coming online and saving it (ironically I'm having the exact opposite issue right now on my car). Again, it's another thing that might suggest a good inspection and rebuild of the carb is in order. When the car is idling in the driveway, take off that air cleaner/snorkel thing and look down the primary side of the carb. If you manipulate the throttle do you see two solid streams of fuel (one for each barrel) from the AP nozzle (located between the two primaries)? If not, look at the AP linkage and see if it has been obviously messed with. If it looks to be 'factory' then you probably have a carb rebuild on your plate. The AP linkage can of course be adjusted, but you'd still get a fuel shot even if it was tweaked. The tps might be doing weird things but I don't know enough about the later first gen rat nests to actually say what. If the tps seems to be in adjustment via doing the fsm tests, I might suggest turning it a few turns one way or the other (I don't think it can hurt anything - someone correct me if I'm wrong; it's just smog after all, I think...) and see if that shifts where the 'stall' or 'jolts' occur. If does, keep experimenting a little and perhaps look through the fsm as to what things in the vacuum rack are happening at approximately those rpms. |
More Pics w/o Cold Air Intake Attached
So I got the time to take off the cold air intake and do a visual inspection w/o help. I wasn't able to see anything moving, but I was shocked at how clean everything is. Maybe that is just the nature of fuel passing through the carb? Regardless of how clean it looks I still am working my way to check the TPS. Thank you for all who have provided assistance and information! This is a great forum.
~TM68 https://cimg9.ibsrv.net/gimg/www.rx7...02396ddef8.jpg Sparkly clean, except for the little triangular passage above the choke area. https://cimg5.ibsrv.net/gimg/www.rx7...a26d479955.jpg The silver collar on top of the carb is for the cold air intake. It seems to have been fashioned onto the carb fairly well by a previous owner. https://cimg8.ibsrv.net/gimg/www.rx7...5f1f34e564.jpg https://cimg2.ibsrv.net/gimg/www.rx7...cc84630246.jpg I believe the "TPS" is that little black wire with the white connector (mid picture). |
Fpr?
Originally Posted by Benjamin4456
(Post 12373499)
A second for whether there's a fpr. Looking at the photos I couldn't see one, but perhaps it's under that mass of hoses in the center. Since it idles and drives I would guess there is; just something to check.
The 4k stall sounds like - maybe - a somehow failing secondary side. As in, perhaps they're opening but no fuel is getting to them - I assume they're still vac. Not sure what condition the car was in before, but it could be a possibility? Does the stall happen at exactly 4k (or some other specific rpm) or is it more so load dependant and around 4k? Will it stall in the driveway (not moving) at the same rpm? Does it catch itself after stalling? The drop in rpm upon initial acceleration is probably a messed up AP, then the primaries coming online and saving it (ironically I'm having the exact opposite issue right now on my car). Again, it's another thing that might suggest a good inspection and rebuild of the carb is in order. When the car is idling in the driveway, take off that air cleaner/snorkel thing and look down the primary side of the carb. If you manipulate the throttle do you see two solid streams of fuel (one for each barrel) from the AP nozzle (located between the two primaries)? If not, look at the AP linkage and see if it has been obviously messed with. If it looks to be 'factory' then you probably have a carb rebuild on your plate. The AP linkage can of course be adjusted, but you'd still get a fuel shot even if it was tweaked. The tps might be doing weird things but I don't know enough about the later first gen rat nests to actually say what. If the tps seems to be in adjustment via doing the fsm tests, I might suggest turning it a few turns one way or the other (I don't think it can hurt anything - someone correct me if I'm wrong; it's just smog after all, I think...) and see if that shifts where the 'stall' or 'jolts' occur. If does, keep experimenting a little and perhaps look through the fsm as to what things in the vacuum rack are happening at approximately those rpms. I'll have to hook the battery up and check to see if it stutters or stalls in the driveway. I hadn't thought to test via that method. Thank you for asking, I'll let you know. Reading your testing method to check the AP also opened my eyes that I can test the linkages and flutter valves directly on the carb. *face palm for not realizing that sooner! I'll let you in on the results of that. I didn't get the chance to read the rest of your post, but after I get another spare moment I'll get back to you on your suggestions! Thank you so much for sharing this knowledge with me. ~TM68 |
FPR is usually for fuel pressure regulator.
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TPS is on the radiator-side of carb, mounted right to it. Looks like a metal boomerang shaped bracket, with a plastic plunger angled down to the primary throttle shaft. Shaft turns (butterflies opening) which moves the plunger in n out, which tells the car what it wants to know.
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I can't find any pictures of it right now but here's a terrible sketch. The blue is the TPS with wire/plug. The oval above it is the fuel sight window.
https://cimg4.ibsrv.net/gimg/www.rx7...6f01f7e557.jpg and as rxtasy mentioned the FPR would be an aftermarket part mounted in the fuel line. If I remember right you said you have a Carter or Holley fuel pump?? The 7psi that pump puts out needs to be regulated down to 2.5-3 or the Nikki will flood. |
Yer artwork's better than mine,lol.
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Here ya go, this part.....
https://cimg3.ibsrv.net/gimg/www.rx7...21085c5773.png |
Just wanted to clarify - ya know, in case someone sees this in the future and is confused by this minor detail - that the single black wire and connector in the middle of the op's last photo is for the 'carb/choke heater'. It has something to do with the bimetal spring and choke assembly. That's all I've got for now though. Hope things are going well.
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Yeah, what he said. Thanks Ben, I removed the incorrect info from my post.
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Man, that Maxwedge is a great guy!
Who else around here would take their carburetor off just to get you a good picture of what he's talking about?!? That's commitment to the cause...
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It takes a village. Anything else ya wanna see?
https://cimg4.ibsrv.net/gimg/www.rx7...64e37119b8.jpg |
Haha, not to steal your thunder Maxwedge, but I thought I recognized that tps photo. A quick Google image search later and... Carb Stripping - foxed.ca.
Still though, it's great to see the sort of community here, and that taking off a carb really is something folks would do. Good greif, my last two posts have been fact checking. I probably ought to stop before I step on someone's toes... Good day all. |
Hey now, I never claimed that first pic was mine! I too got it off the carb stripping guide. The second pic is mine though, when I was rebuilding it.
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Wholly cow haha thank you for sharing the internals!
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Originally Posted by Maxwedge
(Post 12374581)
Hey now, I never claimed that first pic was mine! I too got it off the carb stripping guide. The second pic is mine though, when I was rebuilding it.
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