93 FD running lean with high idle
04-30-11, 09:12 AM
#1
93 FD running lean with high idle
So first off let me say this my first sports car and my first rotary engine. I have driven other FDs, which is what lead me to want to get one.
I was contacted by a friend of a friend because she was selling her 93 FD R1 at a decent price. My only hesitation was the 100k miles on it. The only mods to this car is a boost controller, midpipe/cat back replacement and aluminum AST. The recirculated air from the BOVs is just exhausted, not rerouted to the airbox for louder BOV noise.
I went to check it out and everything looked good. It drove well with no 3000 RPM hesitation, no synchro problems and no funny exhaust. Boost was 10-8-10 and she pulled pretty hard with no hesitation. Idled right around 800 RPM and cold started fine. On a restart after driving it hesitated a little, but with a little gas it fired right up.
I had the service tech at the local Mazda dealer (who rebuilt my friends engine, so I know he knows rotaries) do a compression test. All chambers for both rotors ~690 KPa.
So here's the problem. After doing all of the BMV nonsense, I went to pick up the car to drive it home. It idled ~800 RPM after tapping the accelerator to lower it from 1500 to 800. I let it sit for a little while and then drove home. I was not getting into boost range or driving hard. I then noticed the tach drop to 0 then back to normal revs. I thought well that's strange and it must have been my imagination. Then it did it again at another red light.
Secondly, it is running lean according to the A-F gauge. I was getting some hesitation in 1st gear and it was not accelerating perfectly smooth.
When I got home (only a few miles away) I popped the hood and noticed an intercooler pipe (stock piping, where it starts going down past the exhaust manifold) had pulled away. I got a new clamp and reattached it properly. I restarted the car after a few hours and now it idles around 1200-1500 RPM and poking the accelerator won't drop the revs to 800.
I had read somewhere that the ECU by default runs lean if any of the hoses/vacuum lines are disconnected. So I thought the AF ratio would settle back to stoich. I'm hesitant to start/drive it since it is running lean.
If anyone has any ideas where I should start I would greatly appreciate it. Today I plan on going and getting new plugs and wires and see if that helps at all. Thanks in advanced.
I was contacted by a friend of a friend because she was selling her 93 FD R1 at a decent price. My only hesitation was the 100k miles on it. The only mods to this car is a boost controller, midpipe/cat back replacement and aluminum AST. The recirculated air from the BOVs is just exhausted, not rerouted to the airbox for louder BOV noise.
I went to check it out and everything looked good. It drove well with no 3000 RPM hesitation, no synchro problems and no funny exhaust. Boost was 10-8-10 and she pulled pretty hard with no hesitation. Idled right around 800 RPM and cold started fine. On a restart after driving it hesitated a little, but with a little gas it fired right up.
I had the service tech at the local Mazda dealer (who rebuilt my friends engine, so I know he knows rotaries) do a compression test. All chambers for both rotors ~690 KPa.
So here's the problem. After doing all of the BMV nonsense, I went to pick up the car to drive it home. It idled ~800 RPM after tapping the accelerator to lower it from 1500 to 800. I let it sit for a little while and then drove home. I was not getting into boost range or driving hard. I then noticed the tach drop to 0 then back to normal revs. I thought well that's strange and it must have been my imagination. Then it did it again at another red light.
Secondly, it is running lean according to the A-F gauge. I was getting some hesitation in 1st gear and it was not accelerating perfectly smooth.
When I got home (only a few miles away) I popped the hood and noticed an intercooler pipe (stock piping, where it starts going down past the exhaust manifold) had pulled away. I got a new clamp and reattached it properly. I restarted the car after a few hours and now it idles around 1200-1500 RPM and poking the accelerator won't drop the revs to 800.
I had read somewhere that the ECU by default runs lean if any of the hoses/vacuum lines are disconnected. So I thought the AF ratio would settle back to stoich. I'm hesitant to start/drive it since it is running lean.
If anyone has any ideas where I should start I would greatly appreciate it. Today I plan on going and getting new plugs and wires and see if that helps at all. Thanks in advanced.
04-30-11, 04:49 PM
#2
As a follow on, when I let it fully warm up and take a for a short drive, the idle finally settles down to about 700 RPM and I only have about 12 inHg of vacuum at idle. Does this sound like a popped off vacuum line? Still runs more lean then stoich.
05-01-11, 07:59 AM
#3
Lowering idle by tapping the accerlerator on cold start is normal. There is a system on unmodified cars called the Accelerated Warm-up System (AWS). You can also start the car with the clutch depressed but transmission in gear.
3k hesitation before the car is fully warmed up is also typical.
The stalling on deceleration sounds like a dash-post issue, but if you haven't already, download a copy of the Factory Service Manual from the FAQs in the 3rd Gen. section and trouble shoot.
From your post it sounds like a leaking 'Y' Pipe to Crossover coupler. Typical also, since as you mentioned it's exposed the most to heat from the turbos. Tightening the coupler to solve it may only be temporary. You may have to simply replace it, preferably with a good quality silicone coupler, in the near future.
How are you monitoring A/F? What are your readings. As I understand it, Stoich is an ideal and few engines actually operate there.
3k hesitation before the car is fully warmed up is also typical.
The stalling on deceleration sounds like a dash-post issue, but if you haven't already, download a copy of the Factory Service Manual from the FAQs in the 3rd Gen. section and trouble shoot.
From your post it sounds like a leaking 'Y' Pipe to Crossover coupler. Typical also, since as you mentioned it's exposed the most to heat from the turbos. Tightening the coupler to solve it may only be temporary. You may have to simply replace it, preferably with a good quality silicone coupler, in the near future.
How are you monitoring A/F? What are your readings. As I understand it, Stoich is an ideal and few engines actually operate there.
05-01-11, 11:29 AM
#4
Well that is what concerned me, AWS would not notice the tapped accelerator. It probably ran from a cold start for 10 minutes before it settled down to ~800 RPM. I always start the car in gear so it revs to 1500 RPM not 3000.
Note that, the car isn't actually stalling. It's the tach revving to max revs or min revs, with no engine response. It appears like it's trying to reset or something.
After doing some more forum searching, my A/F readings seem to be inconclusive. It's just a pillar mounted A/F gauge and I do not believe a wideband o2 sensor has been installed. But then again, from the posts I saw people kept seeing very rich readings from the narrow band factory o2. That is not what I see. Mine barely gets to stoich when its fully warmed up.
I am changing all the fluids today so I will take a look and try to identify a crack in the crossover tube. It indeed was the coupler between the y-pipe and the crossover. The car has silicon couplers between them. So that has been connected and is still not running correctly.
Any ideas on the low vacuum at idle? -12 inHg is pretty low as I understand. I guess I will plan on taking off the manifold and try to figure out if any of the lines are off.
Note that, the car isn't actually stalling. It's the tach revving to max revs or min revs, with no engine response. It appears like it's trying to reset or something.
After doing some more forum searching, my A/F readings seem to be inconclusive. It's just a pillar mounted A/F gauge and I do not believe a wideband o2 sensor has been installed. But then again, from the posts I saw people kept seeing very rich readings from the narrow band factory o2. That is not what I see. Mine barely gets to stoich when its fully warmed up.
I am changing all the fluids today so I will take a look and try to identify a crack in the crossover tube. It indeed was the coupler between the y-pipe and the crossover. The car has silicon couplers between them. So that has been connected and is still not running correctly.
Any ideas on the low vacuum at idle? -12 inHg is pretty low as I understand. I guess I will plan on taking off the manifold and try to figure out if any of the lines are off.
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