1986 S4 stumbling loss of power 3k-5k rpm range
03-18-18, 11:19 AM
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1986 S4 stumbling loss of power 3k-5k rpm range
what’s up everyone
im new to the site and had a few questions about an issue I’m having just to hear some people out on their opinions. I just picked up an ‘86 N/A s4 rx7 yesterday. A little background on the car, the guy took it on a trade and the person who gave it to him said it had “a bad seal” Lolol so the dude took the trade and took it to his local Mazda dealer (this was in 2010 the car had 100k miles) dealer quoted him an engine and he had it replaced with an “aftermarket rebuilt engine” since then he’s driven the car maybe 3000 miles and it’s mainly been in storage. After he provided the $6000+ receipt for the r&r and we did some negotiating I bought the car and trailered it home. The cool part is I looked further into some of the paperwork he gave me and it turns out they put a brand new Atkins reman In the car so that was really cool to find out and the dude didn’t even know.
Anyway, I was aware of this issue when I bought it but the car starts up immediately, idles great and sounds super healthy it revs up to 3k perfectly fine but once it goers to 3,000 rpms it will lose power and start hesitating, it will however do this up until 5k rpms, but will not exceed 5k. It does this in neutral or in gear. The guy did put a bottle of cheap fuel injector cleaner in it before we got there and he was driving it around because he thought it may be because it’s been in storage for so long.
Anyway, I have a lot of idea and I’m leaning toward fuel but I want to get some more opinions. I’ve already adjusted TPS and that made no difference. My current plan would be drain fuel tank, replaced plugs, fuel filter and check that injectors are plugged in and most likely get them tested and cleaned. Let me know what you guys think. Thanks!
im new to the site and had a few questions about an issue I’m having just to hear some people out on their opinions. I just picked up an ‘86 N/A s4 rx7 yesterday. A little background on the car, the guy took it on a trade and the person who gave it to him said it had “a bad seal” Lolol so the dude took the trade and took it to his local Mazda dealer (this was in 2010 the car had 100k miles) dealer quoted him an engine and he had it replaced with an “aftermarket rebuilt engine” since then he’s driven the car maybe 3000 miles and it’s mainly been in storage. After he provided the $6000+ receipt for the r&r and we did some negotiating I bought the car and trailered it home. The cool part is I looked further into some of the paperwork he gave me and it turns out they put a brand new Atkins reman In the car so that was really cool to find out and the dude didn’t even know.
Anyway, I was aware of this issue when I bought it but the car starts up immediately, idles great and sounds super healthy it revs up to 3k perfectly fine but once it goers to 3,000 rpms it will lose power and start hesitating, it will however do this up until 5k rpms, but will not exceed 5k. It does this in neutral or in gear. The guy did put a bottle of cheap fuel injector cleaner in it before we got there and he was driving it around because he thought it may be because it’s been in storage for so long.
Anyway, I have a lot of idea and I’m leaning toward fuel but I want to get some more opinions. I’ve already adjusted TPS and that made no difference. My current plan would be drain fuel tank, replaced plugs, fuel filter and check that injectors are plugged in and most likely get them tested and cleaned. Let me know what you guys think. Thanks!
03-18-18, 12:39 PM
#2
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You mean to say it doesn't rev above 5K RPM, or the hesitation doesn't exist above 5K RPM? Primary Injectors work solo until about the RPM, if you search FC3S hesitation you'll see a lot of pages/ about the infamous 3800 RPM hesitation, violent bucking and what not. Sounds to me like it;'s due to the Secondary injectors which come on around that time aren't performing as they should, the common fix for this is adding an addition ground wire either from the ECU or the boost sensor. If you are running fine up to that point I wouldn't worry about fuel as it's the same in all RPM ranges. Only difference is once that much load is put on the engine the secondary injectors start to kick on and supply extra fuel to the engine, if this doesn't happen then you'll have no power.
Good source of information to better understand the 3800 RPM hesitation -
http://fc3spro.com/TECH/FAQ/3800.html
I'm sure others will chime in on this. Hope this helps.
Brandon
Good source of information to better understand the 3800 RPM hesitation -
http://fc3spro.com/TECH/FAQ/3800.html
I'm sure others will chime in on this. Hope this helps.
Brandon
03-18-18, 02:48 PM
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You mean to say it doesn't rev above 5K RPM, or the hesitation doesn't exist above 5K RPM? Primary Injectors work solo until about the RPM, if you search FC3S hesitation you'll see a lot of pages/ about the infamous 3800 RPM hesitation, violent bucking and what not. Sounds to me like it;'s due to the Secondary injectors which come on around that time aren't performing as they should, the common fix for this is adding an addition ground wire either from the ECU or the boost sensor. If you are running fine up to that point I wouldn't worry about fuel as it's the same in all RPM ranges. Only difference is once that much load is put on the engine the secondary injectors start to kick on and supply extra fuel to the engine, if this doesn't happen then you'll have no power.
Good source of information to better understand the 3800 RPM hesitation -
FC3S Pro v2.0:  FAQ - 3,800RPM Hesitation
I'm sure others will chime in on this. Hope this helps.
Brandon
Good source of information to better understand the 3800 RPM hesitation -
FC3S Pro v2.0:  FAQ - 3,800RPM Hesitation
I'm sure others will chime in on this. Hope this helps.
Brandon
03-18-18, 07:38 PM
#4
Full Member
The limited rev range could possibly be another issue but definitely possible it's just your engine isn't getting enough fuel to rev up to that point, if you are even struggling to get up to 5K from 3K then your secondary injectors may not even be working (whether it's wiring, grounding, or the injectors not working themselves). Doesn't matter NA or Turbo but just that the 13B uses primary injectors for 100% of the rev range and secondary injectors that kick on after a certain RPM, typically mid 3K. Essentially the ECU is grounded from 3/4 different grounding wires. Splicing an additional grounding wire to one/all of these, the ECU bracket under the passenger carpet under the dash is from what I've read is a decent spot to ground to.
In the FSM, in the Fuel and Emissions section you can find the complete breakdown of the ECU pins. I just did this to mine to attempt to fix an fueling issue, I added a ground to ECU Plug #3 on Pin 3G, that may or may not mean anything to you but take a look at the FSM break down and it'll make more sense.
But I'd confirm operation of the secondary injectors first, that could be it, or they could be working properly but it's recommended to add these grounds whether or not you have this issue, especially on early S4s, 86-87.5, I've read Mazda fixed it for the later S4s, when they switch from low impedance to high impedance injectors.
Brandon
In the FSM, in the Fuel and Emissions section you can find the complete breakdown of the ECU pins. I just did this to mine to attempt to fix an fueling issue, I added a ground to ECU Plug #3 on Pin 3G, that may or may not mean anything to you but take a look at the FSM break down and it'll make more sense.
But I'd confirm operation of the secondary injectors first, that could be it, or they could be working properly but it's recommended to add these grounds whether or not you have this issue, especially on early S4s, 86-87.5, I've read Mazda fixed it for the later S4s, when they switch from low impedance to high impedance injectors.
Brandon
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