GenII fuel injection

T

tbtapper

New member
I am having an operating anomaly with my FI.

I won't go into too much detail here but basically it appears that the fuel delivery to one rotor goes way lean anytime that a steady state throttle position is set.

I know this because I have dual AFR gages. One stays nice and steady where I want it the other goes so lean that it stops registering. Obviously this is a problem on the back straight at Road Atlanta!

I have done expensive diagnostics/replcements to no avail.

Due to the nature and amount of the details it would be easier to talk with someone off line via phone.

Guess I'm looking for a crash course in Mazda FI tech. Someone out here must know the fundamentals of how the Mazda system works and could suggest a diagnostic tree to chase the problem.

If anyone is interested in helping me out leave a post and phone number/time to call and I'll give you a jingle.

I dreaded this day when the electronics went wonky but there must be a solution.

Thanks

Travers
ITS 19
 
I am having an operating anomaly with my FI.

I won't go into too much detail here but basically it appears that the fuel delivery to one rotor goes way lean anytime that a steady state throttle position is set.

I know this because I have dual AFR gages. One stays nice and steady where I want it the other goes so lean that it stops registering. Obviously this is a problem on the back straight at Road Atlanta!

I have done expensive diagnostics/replcements to no avail.

Due to the nature and amount of the details it would be easier to talk with someone off line via phone.

Guess I'm looking for a crash course in Mazda FI tech. Someone out here must know the fundamentals of how the Mazda system works and could suggest a diagnostic tree to chase the problem.

If anyone is interested in helping me out leave a post and phone number/time to call and I'll give you a jingle.

I dreaded this day when the electronics went wonky but there must be a solution.

Thanks

Travers
ITS 19
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If one rotor is going dead surely your feel a difference in power. If not then it's likely the sensor is bad. If you're using narrow band sensors throw them in the trash. They are really as useful as tits on a boar.

One way to easily see if the injection is firing on both rotors is to hook up some noid lights. Grab a spare CAS and creatively attach it to a high speed drill motor. Something that can spin up to >3800rpm. Die grinders and impact wrenches work well. Plug the CAS into the harness and spin it up. Watch the noid light to see if you're getting a trigger signal to all the injectors. If you are and you're still convinced you're not getting fuel take the injectors out and have them cleaned and tested.
 
Good idea Chris that's about where I'm at. The injectors have been cleaned/balanced and moved around with same result.

Also switched the Lambda sensors from pipe to pipe in the off chance the sensor was at fault with same result.

Added new wireing clips, soldered/shrink wrapped and visually checked wireing from injector to right front harness same result.

changed out the leading ignitor and plugs same result.

Changed out ECU with same result.

Changed out the solenoid/ballast pack with same result.

Checked crank angle sensor (for resistance per factory manual) showed ok.

Checked fuel pressure, stayed steady at various rpm's was fine and steady as the reading went away.

This is why I am getting to the end of my technical "skills". Problem with the damn primaries is that they are buried away under the intake manifold and difficult to access w/o lots of disassembly but I guess I'm getting close.

I wonder why you don't like the narrow band Lambda's? My intent with them was not a metric but simply a balance indicator between front and back rotors. Frankly, to identify this exact kind of problem.

My guess is that the car has always been like this but prior I was too new/lousy a driver to notice. I'm a little better now and notice everyone leaving me for dead any time the road straightens out.

I do have access to the little nifty injector lights and will use them. But it's plain to me that something, somehow, somewhere is telling that one injector to back off, especially when in steady state throttle.

The other rotor is steady and fluctuates what looks like in perfect sequence with throttle blips and steady state so the computer CAN tell one of the injectors to be have properly just haven't isolated the variable that affects the other injector.

I' getting "suspicious" of the injector solenoid ballast pack or the crank angle sensor.

Thanks

Travers
 
The narrow band sensors won't give you a real quantitative indication of mixture. The sensor is only telling you if the measurement is over or under 14.7:1. Here is a .pdf file that contains the output signals of wideband v. narrow band signals. http://www.plxdevices.com/InstallationInst...0UsersGuide.pdf

We've found 13.7:1 to be a fairly ideal mixture ratio for maximum power. The narrow band output has already flat lined at that ratio. A narrow band gauge would simply read rich at that point. The user/tuner would see that and have to assume that the mixture was way too rich and would start pulling fuel, missing the sweet spot of the tune. Like wise, in your situation the sensor may simply be seeing 15-15.5:1 and flat lining. Something that's not ideal for power but not outside the varience possible from rotor to rotor if the front rotor is running at 14.7:1 already. Sorry, but my opinion is resolute, narrow band sensors belong in riced out street cars belonging to kids that don't know better or, more appropriately, in the trash.

See if you can find someone in your area that has a wideband gauge. Or buy your own. The PLX M-300 which is a quite capable unit goes for $299 on Ebay all the time. Take the car to a dyno and do some pulls with the sensor in each primary. Even if you have to use the dyno's single sensor/tail pipe sniffer you'll get a much better indication of overall, averaged mixture than what you're getting now. My guess is that there probably isn't a real problem. The car is a little lean over all, way too lean for max power, and you have one primary showing "lean" on the narrow band gauge which is of little quantitative value.
 
On the lean rotor, do the plugs show a lean condition? If you remove the header, does the exhaust port show a lean condition( a whitish residue)?
Where the primary injectors cleaned and blueprinted? and how long ago?
You may have a tired primary injector...
I believe the primary injectors are the most likely to fail or underperform due to the higher temps their subjected to...their covered by so much of the intake and set in the motor itself thats running at race temps! Less than ideal conditions for injectors that are at least 15 years old...
I recently had my primaries sent out for cleaning,one was found to perform at just 80% of spec...

Good luck
Brian B
#70 ITS NER
 
Travers,
One of the unique aspects of the rotory is that if one or both rotors are lean the header will start to glow almost orange instead of the dark red it is normally. Chris is right dump the 1V o2 sensors and if you can't or don't want to invest in the WBand then get the dual EGT gauge.
 
In all honesty the EGT gauges aren't the hot setup for calibrating fuel mixture. Ignition timing can play as big a part in determining EGT as mixture. A proper mixture with radically retarded timing will give a hot EGT reading. Probe placement makes comparing numbers between different cars very hard. WB O2 sensors do one job and do it very well. Use those to calibrate fuel. On a dyno you can use the EGT gauge to dial in ignition timing once mixture has been enstablished. However, our NA engines will run at MBT anyway so there is no need to be too concerned with burning the engine down by advancing the timing. Turn it up until the power doesn't rise anymore and lock it.
 
...However, our NA engines will run at MBT anyway so there is no need to be too concerned with burning the engine down by advancing the timing. Turn it up until the power doesn't rise anymore and lock it.
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Translation please? (Mega Big Temperature sounds accurate, but doesn't fit the rest of the sentence. )

BTW, Chris, do you have any wisdom to share on a safe timing advance. I got some advice from a well-respected RX-7 supplier to not exceed 28* BTDC, but on the dyno last fall I saw power rising with more advance than that. Got a little worried about running it there, though.
 
Thanks to all for your comments and suggestions. Sad to hear such lack of enthusiasm for the the narrow bands. (wasted $$$)

I think I have gained some insight. After replacing everyting associated with the fuel/ignition system I now have a much better working knowledge of the system.

Two, I learned the importance of really good quality splicing. (ie: crimp and THEN solder that joint, shrink tube twice) Fact is that the "problem" more than likely was an inferior splice on one of the Lambda sensor wires that introduced resistance onto the signal.

Visual evidence showed that the lead plug in no.1 rotor was NOT showing signs of extreme lean mixture. Subsequent testing with a lazer temp gun showed very close temps between the two rotors. And the fuel injector cleaning guy said that all 4 injectors flowed great and were all close in standardized output.

So, my wireing got cleaned up as a result of the process, the injectors cleaned and tested and ignition checked and function verified.

I will still use the AFR's to provide an indication of balance between the two rotors but will go to the dyno for timing. All indications point to a generally rich AFR environment and if the dyno bears this out I'll go to step 2 for adjusting that parameter.

Thanks again for the help. This kind of "conversation" is much more valuable to me than the P&M that goes on in this forum regularly.

Travers

PS: John, come to VIR May 12/14 be nice to meet you.
 
Marty, MBT is a an acronym for a couple relavent terms. In this case Minimum Best Timing. Ignition timing will generally cause power to ramp up as it's advanced to a certain point where power will level off and may begin to fall. The minimum advance required to hit the peak power number is MBT. Some engines allow you to run MBT without invading the knock theshold. Some don't.

We found (and I've heard from others) that something in the area of 27* total advance is the ballpark you want to be in. To find that number we set the dyno up to hold the car at 7000 rpm under WOT conditions. We can stand on the gas all we want and the dyno won't allow the car to rev past whatever you program the limit to be. Using a timing light we adjust the CAS to get the number we want. Let the car cool then make a pull and note the results. Put some more adavnce in and make more pulls till you get it right. On 87 octane pump fuel we've ran up to 35* advance without any detonation. The power quits climbing at ~27* and just levels off. All engines are different and port configuration can play into it as well on NA engines. Forced induction is another animal entirely. What works for one guy may not work for everyone.

When I talk about advance I am talking about total advance at 7000 rpm. Not initial advance which is set at idle. I don't even worry about that number as the engine never runs down there anyway. We set the timing up so that after the stock computer has made all it's corrections we have the number we want.

Another comment I wanted to make was on the topic of reading spark plugs. I wanted to look for an article to quote to back me up (I used to have one saved) but you'll have to search on your own or take my word for it if anyone cares. :) Reading spark plugs is not as easy as pulling a plug and looking at the insulator for color. The first problem is that plugs color very quickly. To do a real plug reading for WOT mixture a "plug chop" is required. What that means is that you'll have to run the engine under the condition you are trying to read and then rapidly cut the fuel and ignition and coast to your pit dead stick. At that point you can pull the plugs and read what they are doing at WOT. Letting them idle for even a few seconds can allow deposits to either accumulate or burn off effectively negating any information you may receive about a prior operating condition. Further, modern pump fuels contain many additives that can either color or cleanse the insulator. If you want to read plugs start with new plugs and race fuel that is largely free of additives. The last word is that the area you want to read is actually inside the plug at the base of the insulator. A plug magnifying light helps you see what you need to see. We used to read plugs all the time with the two-strokes. NASCAR teams still do it on race weekends because electronic monitoring isn't allowed. You'll see them coasting into pitlane dead stick quite a bit. Modern electronics (affordable wideband sensors) have rendered this procedure fairly extinct.
 
Thanks. Good info. Does detonation on a rotary sound like a piston engine? Any how tolerant is it to a little detonation? Will I blow it up if I go too far? I never worried about it too much with pistons. Advance it 'till it pings, then back off a little. Don't know how sensitive these rotaries are.

Now that I think about my dyno runs, we were checking timing at RPM, but with no load. The timing maps I've seen put in a lot more advance at light load than at heavy load, so I was probably not nearly as advanced as I thought I was.

Thanks Chris. You're a wealth of knowledge and very helpful.
 
Rotarys are totally intolerant of detonation. With an NA application and stock seals you will supposedly get a few pings warning but I've never heard one ping. With forced induction it's likely the first thing you'll hear is the sound of the engine running on one rotor. And that's the way my carbon sealed engine went last summer. I've heard detonation in a rotary before. Sounds a bit different than with a piston engine but it's distinct. Not as audible though.

You're right about the timing map assumption.
 
Thank you very much. I'm getting there. Hehe, we've got a little joke in our family. When you were 5 seconds faster than me at M-O I chuckled that you had to be finding your way onto one of the bridges and bypassing half the track. So now my quest for speed is referred to as "looking for the bridge".

Travers, sorry for all this thread hijack, but I'll bet you're appreciating this good info too.
 
I agree with Chris about "reading" plugs. This is probably especially true with rotaries due to the added oil in the fuel to lube the seals. Compounding this even more is the use of colder plugs for the "in race" environment that are not friendly to puttering around the paddock.

My observation with my car was that since I thought I had a severe lean situation in no. 1 rotor there would be some observable difference to no. 2

This was not the case and the noids clearly showed the secondary kicking in the same in both rotors.

My plugs have never looked "nice and tan" as plugs did in the good o'l days. Since I usually don't have a crew it's never been convenient to do a plug chop run and I also get very nervous about r&r plugs from very hot aluminum.

Travers
ITS 19
 
The PLX M-300 which is a quite capable unit goes for $299 on Ebay all the time.
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Sorry to resurrect an old thread like this, but I'm in the market for an AFR for our IT7 car. But I want one that records for later analysis. Does the PLX M-300 do that? I've looked at the web site, but either it doesn't say or I'm too stupid to see it.
 
Sorry to resurrect an old thread like this, but I'm in the market for an AFR for our IT7 car. But I want one that records for later analysis. Does the PLX M-300 do that? I've looked at the web site, but either it doesn't say or I'm too stupid to see it.
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No it doesn't. The R series PLXs do. If I were to buy another one, and I will before long, I think I'd have to look at the Innovate unit. The unit itself is a bit clunky but it logs a/f and RPM and can be set up to do EGT as well. The PLX R series can do that to. What sets the Innovate apart is that it can use either the NTK or Bosch sensors. The Bosch sensors, while much cheaper, are not the most reliable things. They don't tolerate race gas well at all. The NTK is said to respond more quickly as well.
 
No it doesn't. The R series PLXs do. If I were to buy another one, and I will before long, I think I'd have to look at the Innovate unit. The unit itself is a bit clunky but it logs a/f and RPM and can be set up to do EGT as well. The PLX R series can do that to. What sets the Innovate apart is that it can use either the NTK or Bosch sensors. The Bosch sensors, while much cheaper, are not the most reliable things. They don't tolerate race gas well at all. The NTK is said to respond more quickly as well.
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Thanks for the info, Chris. I've been looking at the Innovate unit, too, and I like it. But I'm worried about a couple of things, since it's an IT7 car. First, how far back is the O2 sensor going to have to go to avoid the higher heat of a rotary's exhaust? Second, is the premix going to lead to the quick demise of a potentially long series of O2 sensors?
 
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