another "OMG I HAVE 3800 RPM HESITATION" thread
11-09-08, 12:30 AM
#1
another "OMG I HAVE 3800 RPM HESITATION" thread
so... I have the dreaded 3800 rpm hesitation.
mods list:
rtek 1.7
safc2
AEM wideband
RECENTLY TESTED 720cc secondaries
actually hesitation might be the wrong word. it's more like an impenetrable wall. I can creep past the 3800 mark, but the second I give her gas over that rpm i get massive fuel cut. I have a wideband and it reads all the way lean when this happens and the car will just surge until i let off the gas.
I already looked around for other threads, and I found this one:
https://www.rx7club.com/showthread.p...rpm+hesitation
I tried regrounding the ECU under the UIM and that did nothing. i tried the LED in the injector clip test and got the LED to flash with the pressure sensor vac line plugged while over 3800 rpm and the engine surged as it is supposed to. I also ohmed out my solenoid pack and it read 6.6 ohms all around. My pressure sensor however seems to only want to read about 2.5v no matter if the car is on or off which I find odd. I also checked my TPS and it doesn't have dead spots, and reads about 1 ohm at idle, and about 5 ohms at WOT.
should I just try replacing my pressure sensor? what else could cause this?
mods list:
rtek 1.7
safc2
AEM wideband
RECENTLY TESTED 720cc secondaries
actually hesitation might be the wrong word. it's more like an impenetrable wall. I can creep past the 3800 mark, but the second I give her gas over that rpm i get massive fuel cut. I have a wideband and it reads all the way lean when this happens and the car will just surge until i let off the gas.
I already looked around for other threads, and I found this one:
https://www.rx7club.com/showthread.p...rpm+hesitation
I tried regrounding the ECU under the UIM and that did nothing. i tried the LED in the injector clip test and got the LED to flash with the pressure sensor vac line plugged while over 3800 rpm and the engine surged as it is supposed to. I also ohmed out my solenoid pack and it read 6.6 ohms all around. My pressure sensor however seems to only want to read about 2.5v no matter if the car is on or off which I find odd. I also checked my TPS and it doesn't have dead spots, and reads about 1 ohm at idle, and about 5 ohms at WOT.
should I just try replacing my pressure sensor? what else could cause this?
11-09-08, 02:35 AM
#3
It's not "3800 rpm hesitation". That's just a slight stumble under partial throttle as the primary and secondary injectors transition. Besides, regrounding the pressure sensor is only supposed to fix the problem on '86s.
I'd try to check the engine codes, and see if it throws one for the boost sensor. A used one shouldn't cost you more than $20, so replacing it can't hurt.
It is fishy that it's happening at or around 3800 rpm though, so I would also check that the secondaries are actually firing.
I'd try to check the engine codes, and see if it throws one for the boost sensor. A used one shouldn't cost you more than $20, so replacing it can't hurt.
It is fishy that it's happening at or around 3800 rpm though, so I would also check that the secondaries are actually firing.
11-09-08, 05:31 AM
#4
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11-09-08, 08:46 AM
#5
HAILERS
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You SURE your getting vacuum on the hose to the boost/pressure sensor? The 2.3vdc to 2.7vdc is with the hose off the sensor, whether at idle or just key On. If the hose is connected, and engine running, the figure should change.
Or put the key to ON and a meter on the brown/red output wire. Put a spare piece of vacuum line on it and suck and blow into the line. The voltage should be changing on the meter as you do so.
Even better, if you have a MITTYVAC, you could put pressure and vacuum on it using that.
If you have that SAFC connected to it, I'd remove that item.
AND a 87 turbo II could easily been built in 1986. Look at the boost/pressure sensor. See if it has two wires in the ground socket. That would be the brown/black wire. Might be two pure black wires. See ALLDATA for the Mazda FIX for this problem (cost dough to do that).
Or put the key to ON and a meter on the brown/red output wire. Put a spare piece of vacuum line on it and suck and blow into the line. The voltage should be changing on the meter as you do so.
Even better, if you have a MITTYVAC, you could put pressure and vacuum on it using that.
If you have that SAFC connected to it, I'd remove that item.
AND a 87 turbo II could easily been built in 1986. Look at the boost/pressure sensor. See if it has two wires in the ground socket. That would be the brown/black wire. Might be two pure black wires. See ALLDATA for the Mazda FIX for this problem (cost dough to do that).
Last edited by HAILERS; 11-09-08 at 08:52 AM.
11-09-08, 02:17 PM
#6
yea there were 2 black wires going to the ground socket, so I checked for continuity with the battery and just spliced the extra ground into one of them.
I did the voltage tests on the pressure sensor with the vac line plugged, so that would explain why the reading never changed. I'll try again tonight and do what you said HAILERS.
and yes i mean kohm...
rotaryrocket may be right though. I think there is something more wrong here than hesitation since I can't accelerate past 3800rpm under load at all. the engine doesn't hesitate, it says no.
I did the voltage tests on the pressure sensor with the vac line plugged, so that would explain why the reading never changed. I'll try again tonight and do what you said HAILERS.
and yes i mean kohm...
rotaryrocket may be right though. I think there is something more wrong here than hesitation since I can't accelerate past 3800rpm under load at all. the engine doesn't hesitate, it says no.
11-09-08, 02:33 PM
#7
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I'd be really, really cool, if you went for a ride with a digital meter backprobing one of the seconday injector wires at the ECU.
You'd see alterantor voltage on that wire until you hit 3800 under load, then the 13 vdc would drop down several volts. Like down to 8vdc as the secondarys came online.
If the voltage stayed at 13vdc, then the ECU isn't putting them online at 3800rpm.
In general, what happens, is you hit 3800rpm under load. The primarys output is cut in half and the secondarys match the primarys voltage at the same time. So if you were hard on it and the voltage on the primarys was 5vdc at 3800rpm, it would then come up to Maybe 7 or 8vdc and the secondarys would now come on and match that same voltage. I'd use the word duty cycle instead of voltage but most common meters don't have that feature. So do. Like Fluke 88.
You'd see alterantor voltage on that wire until you hit 3800 under load, then the 13 vdc would drop down several volts. Like down to 8vdc as the secondarys came online.
If the voltage stayed at 13vdc, then the ECU isn't putting them online at 3800rpm.
In general, what happens, is you hit 3800rpm under load. The primarys output is cut in half and the secondarys match the primarys voltage at the same time. So if you were hard on it and the voltage on the primarys was 5vdc at 3800rpm, it would then come up to Maybe 7 or 8vdc and the secondarys would now come on and match that same voltage. I'd use the word duty cycle instead of voltage but most common meters don't have that feature. So do. Like Fluke 88.
Last edited by HAILERS; 11-09-08 at 02:56 PM.
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11-11-08, 06:19 PM
#9
I tried to backprobe the secondaries while driving and it's just not happening, the probe keeps coming off no matter how much electrical tape i put on it. is there a way to trick the ECU into thinking it's under load when it isn't?
btw, i should see no voltage at the secondaries when the car is idling correct?
btw, i should see no voltage at the secondaries when the car is idling correct?
11-11-08, 06:53 PM
#10
I tested the pressure sensor again and it sits at:
1v plugged in car warmed up and idle
2.3v unplugged car idling
i can change the voltage by sucking/blowing on the vac line between about 1v and 2.5v
if i'm doing this right, and i think i am, i can backprobe any of my 4 injectors at the ECU and get 14v while the car is idling.
does that make any sense at all? or should I try and borrow/buy another ECU and see if that's my problem?
The Rtek that's in there is almost brand new and I was the one who had the chip installed there. What could I have done to damage the ECU if it's broken, or could Rtek just installed the chip wrong?
1v plugged in car warmed up and idle
2.3v unplugged car idling
i can change the voltage by sucking/blowing on the vac line between about 1v and 2.5v
if i'm doing this right, and i think i am, i can backprobe any of my 4 injectors at the ECU and get 14v while the car is idling.
does that make any sense at all? or should I try and borrow/buy another ECU and see if that's my problem?
The Rtek that's in there is almost brand new and I was the one who had the chip installed there. What could I have done to damage the ECU if it's broken, or could Rtek just installed the chip wrong?
11-11-08, 07:15 PM
#12
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No. There's voltage at all the injectors anytime the key is to ON or better. If the engine is running the voltage will be what the alt is putting out.
Injectors work by the ECU putting or pulsing a ground on the injectors. It's the pulsed gnd that makes them open and shut. Voltage is there all the time.
It sounds like your boost sensor is working. If memory serves the voltage goes up as the vacuum goes towareds zero and boost comes online.
What's the part numbers on the Boost sensor? N???
The 2.3vdc sounds as normal as can be. I forget what the voltage is at idle with the vacuum hose on the sensor. I Might look tomorrow.
You can trick the ECU into making the secondarys come online any time you reach 3800rpm. Just remove the vacuum line off the boost sensor and plug the vacuum line at that end. That's all there is to it.
Rev it to 3800 rpm in the driveway and they'll come online. But it'll sutter and sound crapy. Too little air incoming and the fuel from the secondays not getting atomized enough in my humble opinion. But they will come online like that.
Injectors work by the ECU putting or pulsing a ground on the injectors. It's the pulsed gnd that makes them open and shut. Voltage is there all the time.
It sounds like your boost sensor is working. If memory serves the voltage goes up as the vacuum goes towareds zero and boost comes online.
What's the part numbers on the Boost sensor? N???
The 2.3vdc sounds as normal as can be. I forget what the voltage is at idle with the vacuum hose on the sensor. I Might look tomorrow.
You can trick the ECU into making the secondarys come online any time you reach 3800rpm. Just remove the vacuum line off the boost sensor and plug the vacuum line at that end. That's all there is to it.
Rev it to 3800 rpm in the driveway and they'll come online. But it'll sutter and sound crapy. Too little air incoming and the fuel from the secondays not getting atomized enough in my humble opinion. But they will come online like that.
11-11-08, 07:21 PM
#13
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Maybe it's me, but the picture is too dark to tell anything. Get a lamp on the subject and take another picture. Unless someone else can see what the deal is.
What happens if you ease past 3800 rpm and then when you reach, say 4500 rpm and slam the pedal to the floor? Stutter or run halfway decent?
What happens if you ease past 3800 rpm and then when you reach, say 4500 rpm and slam the pedal to the floor? Stutter or run halfway decent?
11-11-08, 08:32 PM
#14
the boost sensor is "N318"
and I tried taping the vac line to the boost sensor closed but it wasn't working so I didn't think it would work. maybe it just wasn't sealed all the way, so i'll give that another shot. or maybe it was working and it ran fine because there wasn't too much gas because the secondaries weren't coming on?
if I try to ease past 3800rpm and then get on the gas the same thing happens. it's like the secondaries aren't coming on at all.
i'll get another picture as soon as i can of those connectors. I swapped my front wiring harness (not the emissions harness that the injectors are on) with that of another s4 t2 because mine was destroyed by the previous owner, and the original harness didn't have those connectors on it.
and I tried taping the vac line to the boost sensor closed but it wasn't working so I didn't think it would work. maybe it just wasn't sealed all the way, so i'll give that another shot. or maybe it was working and it ran fine because there wasn't too much gas because the secondaries weren't coming on?
if I try to ease past 3800rpm and then get on the gas the same thing happens. it's like the secondaries aren't coming on at all.
i'll get another picture as soon as i can of those connectors. I swapped my front wiring harness (not the emissions harness that the injectors are on) with that of another s4 t2 because mine was destroyed by the previous owner, and the original harness didn't have those connectors on it.
11-14-08, 03:05 PM
#16
alright, so I still don't know what is wrong with my fuel system and I have developed a new fuel related problem.
about every other time I let off the gas and change to idling in neutral the revs will bounce like i have a big vacuum leak. I look at my wideband and it will go all the way lean at every bounce. also I can make the car stop doing this by just tapping the gas, which makes me think the only possible culprit could be the TPS. so the car is cutting the fuel at idle now, but only sometimes.
could a faulty TPS cause this? is the TPS "arm" supposed to remain in contact with its lobe on the TB at all times? because even though mine tests fine electrically its "arm" stops extending at about half throttle.
about every other time I let off the gas and change to idling in neutral the revs will bounce like i have a big vacuum leak. I look at my wideband and it will go all the way lean at every bounce. also I can make the car stop doing this by just tapping the gas, which makes me think the only possible culprit could be the TPS. so the car is cutting the fuel at idle now, but only sometimes.
could a faulty TPS cause this? is the TPS "arm" supposed to remain in contact with its lobe on the TB at all times? because even though mine tests fine electrically its "arm" stops extending at about half throttle.
11-14-08, 04:24 PM
#17
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Put the meter on a PRIMARY wire. Start the engine and look at the voltage. Now either rev the engine but even better drive down the street. You'll notice the voltage will drop down. Down in the seven volts give or take. Can't miss that. You don't see a pulsing. You see a voltage drop. The pulses are in Milliseconds, you you can't and the meter cant' SEE that rapid a switching action. If looking at the SECONDARY injectors, the voltage will stay steady. Til you hit 3800 rpm under load and then the steady 12-13 volts will suddenly show what? way down in the five to seven volts area. Meaning they are working.
11-14-08, 04:30 PM
#18
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From your original post, that sounds just like the secondary injector plugs are off or their injector plugs have been spliced to the stock wiring and there is an open wire on each secondary connector. But if you read 12vdc on each injector wire on the ECU's small plug, that can't be the problem.
All four injector wires should have batt voltage on them with key ON. If one is missing, then it's the problem injector/plug/wire.
The injectors turn off when you let off the pedal while driving. Supposed to do that. Turn back on when the revs get down to ??? 13-1400rpm. Sounds like the TPS is not set right. Do not ohm the sucker out. Get the engine HOT. Idle the engine. Backprobe the green/red wire n the ECU. It should read approx one volt. If not, turn the screw til it does. Hot ENGINE. OR backprobe the green/red wire on the TPS connector instead of the ECU.
TPS is at full range just about the same time the secondary thottle plates start opening. Normal. TPS is at one hundred percent then, NOT at full pedal.
All four injector wires should have batt voltage on them with key ON. If one is missing, then it's the problem injector/plug/wire.
The injectors turn off when you let off the pedal while driving. Supposed to do that. Turn back on when the revs get down to ??? 13-1400rpm. Sounds like the TPS is not set right. Do not ohm the sucker out. Get the engine HOT. Idle the engine. Backprobe the green/red wire n the ECU. It should read approx one volt. If not, turn the screw til it does. Hot ENGINE. OR backprobe the green/red wire on the TPS connector instead of the ECU.
TPS is at full range just about the same time the secondary thottle plates start opening. Normal. TPS is at one hundred percent then, NOT at full pedal.
Last edited by HAILERS; 11-14-08 at 04:35 PM.
11-15-08, 03:06 PM
#19
The bouncy idle started happening after I adjusted the TPS and I think it is adjusted incorrectly because the car was not fully warmed up when I did it. I'm going to re-adjust the TPS and see if that solves that problem at least. I knew that the injectors turned off on deceleration, and thanks for clarifying that the TPS is done opening at about half throttle.
I will go test the voltage again at the ECU and see if i can see the voltage drop you're talking about.
I will go test the voltage again at the ECU and see if i can see the voltage drop you're talking about.
11-15-08, 06:05 PM
#20
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Once upon a time I had a bad 3800 hesitation. But it never recovered as I held the pedal down. It turned out the front secondary had a splice in one of the wires pulled apart. So I was hitting 3800 rpm......the primarys duty cycle was cut in half as it's supposed to.....only the rear secondary came on to match the duty cycle of the primary injectors.............so the engine went phhhhhhhhhhhhhhhhht! until the pedal was let off then it ran like the champ it is.
Looking at the small ECU plug with key ON showed three of the injectors had batt pwr but one did not, the green/white one. So it was two hours of ah shucks lifting the upper intake out of the way to see the front secondary injector and eeeek! one of the two wires hanging in mid air. Called poor craftsman ship by yours truly.
That's two hrs from start to job done.
Looking at the small ECU plug with key ON showed three of the injectors had batt pwr but one did not, the green/white one. So it was two hours of ah shucks lifting the upper intake out of the way to see the front secondary injector and eeeek! one of the two wires hanging in mid air. Called poor craftsman ship by yours truly.
That's two hrs from start to job done.
11-20-08, 03:57 PM
#21
so I went to adjust my TPS before I took the UIM off to check my injector wires, and I noticed that depending on if I let off the gas pedal very quickly or slowly there is a 0.300 kOHm difference in the reading. I adjusted my TPS for when I let off slowly, but what is this all about? bad throttle cable? since the throttle cable is covered, is there any way to re-lubricate it?
more to come as I am in the process of removing said UIM...
more to come as I am in the process of removing said UIM...
11-20-08, 05:53 PM
#22
I pulled the UIM and checked both secondaries. They both have 12v, and they both have 2.6 ohms resistance. I think one of the plugs was only half on, and if thats the problem, then i'll be VERY happy.
both of the primaries looked fine as well, plugs secure, and I checked at the ECU and they both were getting 12v as well. No fuel was leaking in the area either, so the injectors aren't faulty. I'm just going to put everything back together since I don't see anything wrong
both of the primaries looked fine as well, plugs secure, and I checked at the ECU and they both were getting 12v as well. No fuel was leaking in the area either, so the injectors aren't faulty. I'm just going to put everything back together since I don't see anything wrong
11-20-08, 07:22 PM
#23
drove her around again after putting everything back together. idle is rock solid except when you go into neutral and let the car idle while cruising to a stop. ONLY then will the idle bounce by about 200 rpms, and even then not until the car is warmed up, and not every time. there is still the impassible fuel cut wall under moderate/heavy acceleration, but not light acceleration, at 3800rpm.
WTF??? I CANT FIND ANYTHING WRONG AND YET ITS STILL BROKEN!
WTF??? I CANT FIND ANYTHING WRONG AND YET ITS STILL BROKEN!
