Maxthe7man

I think I may have stumbled upon something that may be an engine killer on the TII, I wanted to check my fuel pump voltages at various speeds when driving, so I rigged up my voltmeter to the fuel pump harness and went driving, what I found is that with colder air temps, the ecu does not command the resistor switch over relay to give full voltage to the pump at low intake temps, but when its cold, I get massive boost creep, without a boost controller, wastegate only, I hit 14 psi in top gears easily, with a ported wastegate..
Mods are as follows: 87 TII
TID
Straight through exhaust, 2 rear mufflers only
no acv
no air pump
s-afc
walbro 255 lph
3mm streetport
Outside air temp was 25f..
With a temp probe in the intercooler, I had to do alot of low gear boost runs to get the intercooler temps up, I partially blocked off the intercooler to get the temps up and low behold, the ecu switched over to higher voltage at the pump, Once I got to 90f intake temps I was reading 14.8 volts at the pump, previously it held at 10.5-11.00...
I do not know the parameters for the intake sensor, I should check the resistance, but it looks like the ecu holds pump voltage back until the temps get higher in the intake tract, once they hit a certain level, it nails the pump up to full voltage..
Me or my car might be totally screwed here, but it looks like that running highboost with cold intake air, could create a lean condition, by not having enough fuel pump voltage, I am starting to lean towards tossing the resistor package, and running high volts all the time once I replace stock fuel reg with a malpassi or vortech FMU...
If others have some insight on this, feel free to blow my theory out of the water or add to it...
I also found that the stock pressure regulator is actually a 2 step regulator and not a rising rate, it seems to have two settings, 25 and 40 psi and thats it, so with 10 psi of boost, one would only have 30 pounds pressure difference across the injectors, and I think the 550's are rated at 43 pounds pressure difference... Can't wait to go stand alone efi..Max

Maxthe7man

bump

Wankel7

Man that is a very intresting find! Seems like the best alternative is to wire the pump for full voltage all the time.

James

HAILERS

I'm just a newbie, but it always has seemed to me that a person with a turboii should have a fuel pressure gauge as the most important tool to decide if he is running lean or not. That car when not under boost is supposed to have 28.4 psi in the fuel rail. STomping on the pedal removes the vacuum that is controling the regulator to 28.4, and the regulator now goes to its 35.6-37psi schedule. I make no argument against the pump should be getting 12v at boost, its just that it seems to me you should have a fuel pressue gauge to monitor if the fuel pressure drops below the 35.6 to 37psi value. That seems just as if not more important than having a air/fuel meter. But then again, if a fuel pressure gauge was as important as I think, I would have read some post about fuel pressue gauges, and I don't. So I'll keep my newbie status until further notice. P.S I think I'll more or less try duping your experiment for kicks. Don't have the ability to monitor the intercooler, but the manual shows the air inlet temp resistance values for different temps and maybe I can work something out. Have fun. I'm sure I missed something when you were talking about how the fuel pressure should read 40plus psi.

Maxthe7man

I actuallu had a fuel pressure guage hooked up at the same time, but I did not like the idea of driving with it, its just a test guage, not a full time installed monitoring gauge, I was seeing 25 psi at idle, and when I tricked the regulator to close, I would see 40 pounds on the rail..
I think you could see the rail pressure drop off if the fuel pump was still only getting the low volt signal from the ECU, and that's the potential problem I am talking about..
I found the pressures in the FSM, just like the ones you stated, mine read 40 psi, but that could just be my guage, but its close enough, the part about the injectors though is that they are rated at 550cc at 43psi pressure differential across the injector, with 10 psi of boost though,with the mazda fuel pressures in the range of 35 to say 40 psi , you effectivley only have 25 to 30 pounds pressure differential across the injectors, which means you are not going to get near 550 cc worth of fuel out of each injector.. I think a rising rate FPR might be a good thing to do for anyone thinking of running more boost on a TII, along with ditching the resistor pack for the fuel pump and rewiring to get full battery volts all the time..
So with the rising rate FPR, you could set it at a 1:1 ratio and set the base pressure at 43 psi, so you start with actually pressure the injectors are rated for, the increase the fuel pressure 1 psi with every 1 pound of boost, so you could maintain the same pressure differential across the injectors on boost, an s-afc would be needed though to control the fueling at idle, as being in a vaccuum, 43 psi would be to much, and the stock ecu would probably flood the car out..
If you could hook up a variable resistor that you could adjust from the drivers seat in place of the intake air sensor, that might give you and idea of what its trying to accomplish within the stock fuel maps, and how it plays with the fuel pump voltage according to intake temp, when it gets warm here again I would like to see the voltages the pump gets then but, I will probably be running a stand alone by then and it won't matter to much..
I was just trying to see what the stock fueling strategy was like before I went stand alone, as I would like to program the stand alone to adhere to some of the concepts of the stock ecu so that the car remained as docile off boost as it does now. There seems to be alot of ancillary systems in the TII just to control the car off idle while mainting enough fuel capacity for when its on boost, I think all the gizmo's like the resistor pack, 2 step pressure regulator and such was mazda's way of avoiding putting more than 4 injectors on the engine, like putting to 350's on for low speed idle. then another 2 400cc's and then another 2 550cc's for boost.. All this added crap was just a way of taming the size of 550 cc injectors for emmisions and driveability....Max

Scott 89t2

I really want someone another person to test this. I was sure the pump voltage was controled off the tps. and was only at 9v at idle and very light cruising. I'm also positive the stock FPR is raising... but I've never checked. if you didn't have the gauge hooked up for driving you would not know yourself though...

maybe your car is just screwed

HAILERS

It never occured to me about the pressure differential across the injector at say a boost of 10psi vs the 40 or so psi in the rail . Something to chew on. I put a fuel pressue gauge on my car tonite and did a leak check on it and will play around on the hwy tomorrow. I've got some investigating to do first. I'm reading 38 psi at idle and it should be 28. Must have a vac line off the pr or the solenoid is'nt working right. I checked this car out about four or five months ago and all was well then. Oh well.

Maxthe7man

Yeah , if one of those lines came off or the solenoid is no good, you may not be getting the dropped pressure..
Scott, When watching my voltmeter, I saw no connection between fuel pump voltage and throttle position, I know my TPS is good, but it didn't seem to play on it at all...Max

Scott 89t2

this is weird, it almost makes a fuel pump rewire worthless... but I guess in normal weather/ normal conditions the intake temps hit 90? what if you have a nice FMIC? then the problem would be much worse!

Turbo Timmy

I don't know how this is related but this (similar) happened to me this Fri.

I took my car to the track (temps in the 40-50's). I leave my car idling while driving through the staging lanes. Anyway i'm sure my IC was a little warm, but I could barely hit 10 lbs!

As soon as I got my car out on the highway and drove @ 50 for about 5 minutes then stomped it it went right up to 15...

So while IC was hot low boost, as soon as the IC got nice and cold boost skyrocketed. I know it's hard on the engine but man did it pull strong!

Mods are intake (+tid), RB exhaust, ported wg, fuel++++

Keith

Hey, I came to the conclusion that the lower voltage to the fuel pump was unnecessary, so when I rewired my fuel pump, I eliminated the resistor package (actually, the ECU would not release the fuel pump resistor relay, but the above sounds so much more academic, don'tcha think? ). I have been running this way for close to 6 months. Here are the results. On cold starts, the car is normal. On warm starts, I need to use the fuel pump cutoff switch. Idle is perfectly smooth. Low rpm running is closed loop (Oxygen sensor and ECU maintain stoich no problem). Heavy throttle response immediately goes rich, and the car performs very well to over 7000 rpm in gears 1-4 (haven't tried 5th yet, too many jerks on the road here in Atlanta). Plugs do not carbon up or foul. So, I'm happy, and will never wire the resistor back in. Happy New Year All!

Irv, Keith's dad
'87 TII

Henrik

I ran with a voltmeter on the signal for a while and the pump voltage seems to be based on AFM readings which would make sense as fuel delivery should follow airflow. I could keep it at 9v at most rpm's by being light on the throttle and 12v at most rpm's by being heavy. If I gave it WOT at low rpm's, the relay didn't cut over 'for a little bit', ie until the AFM reading got to a certain level (its kinda hard to say for sure as the delay from low air flow to high airflow is rather short )

I have also read that he stock FPR is raising (just not adjustable). Remember that the solenoid will connect the regulator to manifold pressure which with the car stationary is hard to make positive hence the service manual only gives two test points (vacuum applied and 0 pressure, both at idle) Somebody with a fuel pressure gauge can test this by applying a pressure signal to the regulator at idle and tell us what it does (don't go over 10psi).

Henrik
87TII

HAILERS

The Fuel pressure regulator: With the exception of Hot Start conditions, the fuel pressure regulator solenoid puts a vacuum on the regulator all the time you are driving. That puts the regulator on the low schedule which is something like 28psi. When you slam your foot to the floor the intake manifold does not have a vacuum anymore, which in turn removes the vacuum from the regulator. The regulator now goes to its high schedule which is close to 40psi. The moment you let your foot off the gas a vacuum is formed in the intake manifold and a vacuum is put back on the regulator, switching it back to the low 28psi schedule. BOTTOM LINE....Its your foot that controls the high and low schedule more so than the fpr solenoid which does NO switching back and forth during driving. There was a thread on this subject about four months ago.

HAILERS

I tied my fuel pressure gauge to the windshield wiper this morning and went for a ride. After a bit I realize I was incorrect in my understanding of how the fpr works. I thought it had only a high and low schedule. Wrong. Its a variable regulator(I know, you all knew that). As you cruise along at 70mph and gradually apply throttle the pressure increases incrementaly. I was in forth gear at 70. Stomped the pedal. Noticed that when the voltmeter to the pump increased from 9.8v to 11.8 volts, it was the same instant that the boost meter hit b/t 4 and 5 psi. So I figured that the fuel pump was tied to the output of the boost or pressure sensor. Was fat and happy until I turned around for the return trip. Put the car in fifth and stomped the pedal. Pressure gradually rose until the pump switched to 11.8v when it jumped to 45psi as it did previously in forth. The only diff was the boost was 7psi at the switchover. I think I bought a defective gauge by the way. It reads about 35psi cruising at 70 and when the pump comes on line at 11.8v, I read a good 45-46 psi. Brand new 40 buck gauge. I'm going to put my old gauge on it and compare. When at full boost I did not notice any deterioration of the fuel pressure at 45psi, but then again, theres way too many people off work today. Later. Hi there Irv.

HAILERS

HENRIK..... I just pulled 10psi using a Mittyvac on the vac hose to the regulator. The result was an almost perfect 50psi on the fuel pressure gauge. Car idling.

Maxthe7man

That's interesting... I can't get my fuel pressure over 43 psi on my guage, I think my walbor pump exceeds the return capacity of the FPR, thats the only reason I see 43psi.. I applied 12 psi with a hand pump to the fpr, the pressure on mine did not rise at all, even with the fuel pump jumpered to higher volts... My FPR could be screwed, and I had some doubts about it a couple of months ago, when I could not get my car to lean out at idle...
I ran the car a bit with the fuel pump jumpered to battery voltage, it seemed to be ok with it, but noticed I had to trim the s-afc down in the lower rev range a few times, and the car let out some horrific bangs, I am sure it shot some flames out the back, I felt them through the seat..
There may be two or more controls over the voltage switching to the pump, does the AFM have its own temp sensor circuit as well? I am wondering if its a combination of boost pressure and the ais..
Hailers--> When you did your test, what was the ambient temperature??
So yours seemed to respond to being on boost, but the boost pressure was not consistent?...Max

HAILERS

I used a Mittyvac, teed into the fuel pressure regulator AND the Autometer boost gauge. At idle I put 10psi as read on the Autometer gauge, on the fpr. The fuel pressure gauge read 50psi. Just to make sure, I swapped everything over to my 87NA and with 10psi put on the fpr, I got 50psi on the fuel pressure gauge(brand new about 39bucks gauge that had better be working right or else). I know the NA never sees boost, but its the same regulator thats used on the turbo , I am almost sure. It was early morning and the temp was 35 degrees.
The airflow meter has a air temp sensor and its output goes to pin 2J on the ECU. Should read 2~3v at 68 degrees temp.
Did not know that you had a Waldo fuel pump. The stock pump put out 71-92psi so it should'nt matter if the thing had 9 or 12 volts if your only looking for say 50psi on the rail, and idling.
About what causes the Fuel pump relay and resistor to swap to over 9 volts, I came to the conclusion its more than the boost sensor. Must be a combination of the sensor and rpm with maybe a little afm chunked in to complicate things.
Your fpr seems a little odd. On both my turbo and na regulators the fuel pressure rises to 50max when 10psi is applied to the diaphram.
I think I might have a pulsation damper problem with the N/A. The gauge needle has *bounce* to it at idle. I think the pulsation damper is supposed to remove those pulses. Turbo does not do it.

Maxthe7man

Hmm, real intersting that your n/a seems to be rising rate, I never thought of checking my n/a or the n/a fuel rail and fpr I have sitting on the bench....Driving today, I was on boost, temp was about 10-15 deg outside, I was running with the resistor pack back in, and it never saw high voltage to the pump all day long, except for when the car really got cold when it sat for 3 hours, on startup I saw 14 volts for about half a minute, then it went back to about 10 volts.... I am wonder what the range now is of the FPR, there must be a limit to how much it can raise fuel pressure, maybe thats why running more than 10 or 12 psi kills tII's, the FPR is maybe only good up to 50 psi? I was reading the fsm today, by their account it is just a to step reg, they say nothing about tracking to fuel pressure, but that may be outside of the scope of the FSM itself....Max

HAILERS

Just put your testing fuel pressure gauge on the line and start the car and let it idle. Put your vacuum pump on the fpr and the fuel pressure WILL rise. I hit 50psi and it would go no further. When I hit 50psi the pump was pumping 10psi pressure. If its 10-15 degrees outside, I stay indoors. I've been driving the na around today with the fuel gauge tied to the wipers, and it hits a max of 39 psi and a low of 30 if I let off the throttle rapidly. The turbo was hitting around 45psi at boost, 35degrees air temp. I only see a touch below 8psi under boost. Not much in the way of mods. If temp was a factor, I would think that the colder it was, the sooner you'd see the higher voltage. Oh well.