Fuel pressure during cranking?
#1
Full Member
Thread Starter
Join Date: Jul 2004
Location: Sacramento
Posts: 164
Likes: 0
Received 0 Likes
on
0 Posts
Fuel pressure during cranking?
I tried a search, but I had no luck. I know what fuel pressure should be at pump and when tied and engine off with primer jumped, but what about while cranking under normal conditions?
I see 20 psi while the engine is cranking, is this normal?
Plus, 6 ohms at the injector solenoid is ok correct?
I have a huge flooding problem, I am trying to isolate a cold start issue I have posted in another thread.
Thanks for the help.
I see 20 psi while the engine is cranking, is this normal?
Plus, 6 ohms at the injector solenoid is ok correct?
I have a huge flooding problem, I am trying to isolate a cold start issue I have posted in another thread.
Thanks for the help.
#4
Lives on the Forum
It should have minimum 30psi.
According to the FSM, it should actually spec out to 40psi?
There is an FPR solenoid that clicks open, and the FPR should see "0psi", so you're supposed to be seeing 40psi at the rails.
20psi is just too low...
-Ted
According to the FSM, it should actually spec out to 40psi?
There is an FPR solenoid that clicks open, and the FPR should see "0psi", so you're supposed to be seeing 40psi at the rails.
20psi is just too low...
-Ted
#6
Full Member
Thread Starter
Join Date: Jul 2004
Location: Sacramento
Posts: 164
Likes: 0
Received 0 Likes
on
0 Posts
Well my pressure is fine if I jump the pump. . I have a areomotive FPR set to 36 psi when I jumped the yellow clip, but when I try starting it (with jumper properly removed) I only see about 20 psi .
I thought the PFR solenoid only plays a role when the engine is running and vacuum is present, I'm confused now...sigh.
I thought the PFR solenoid only plays a role when the engine is running and vacuum is present, I'm confused now...sigh.
Trending Topics
#8
HAILERS
Join Date: May 2001
Location: FORT WORTH, TEXAS,USA
Posts: 20,563
Likes: 0
Received 21 Likes
on
19 Posts
Just reinforcing the above. The pressure should be 37 to 40psi during the start. Mostly because there's no vacuum to pull a STOCK FPR down to the 28-30 psi range.
So? Why not start with the jumper installed so you'll have regular pressure???
And if there's a open in the water thermo sensors wires to the ECU, then the injected amount will be toooooo litttttlllllle and cause for a very hard start during cold starting conditions. An open wire will not effect a hot engine start though due to the ECU defaulting to 176 F if the wires are off the water thermo sensor or there is an open to the ECU.
So? Why not start with the jumper installed so you'll have regular pressure???
And if there's a open in the water thermo sensors wires to the ECU, then the injected amount will be toooooo litttttlllllle and cause for a very hard start during cold starting conditions. An open wire will not effect a hot engine start though due to the ECU defaulting to 176 F if the wires are off the water thermo sensor or there is an open to the ECU.
#9
Full Member
Thread Starter
Join Date: Jul 2004
Location: Sacramento
Posts: 164
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by HAILERS
Just reinforcing the above. The pressure should be 37 to 40psi during the start. Mostly because there's no vacuum to pull a STOCK FPR down to the 28-30 psi range.
So? Why not start with the jumper installed so you'll have regular pressure???
And if there's a open in the water thermo sensors wires to the ECU, then the injected amount will be toooooo litttttlllllle and cause for a very hard start during cold starting conditions. An open wire will not effect a hot engine start though due to the ECU defaulting to 176 F if the wires are off the water thermo sensor or there is an open to the ECU.
So? Why not start with the jumper installed so you'll have regular pressure???
And if there's a open in the water thermo sensors wires to the ECU, then the injected amount will be toooooo litttttlllllle and cause for a very hard start during cold starting conditions. An open wire will not effect a hot engine start though due to the ECU defaulting to 176 F if the wires are off the water thermo sensor or there is an open to the ECU.
Well I know for sure my thermo sensor is good. I ger about 2.5 volts at ECU and get 4v when I unplug it, so thats fine. I am going to look for fuel resistor solenoid specs since I cant find it in the manual and go from there. Hopefully I am heading in the correct direction. I might also double check the AFM again...who knows? Some thing just aint right.
#11
I'm a boost creep...
Join Date: Jan 2002
Location: Auckland, New Zealand
Posts: 15,608
Likes: 0
Received 8 Likes
on
8 Posts
Originally Posted by RETed
There is an FPR solenoid that clicks open, and the FPR should see "0psi", so you're supposed to be seeing 40psi at the rails.
Originally Posted by rhythmfunk
Well my pressure is fine if I jump the pump. . I have a areomotive FPR set to 36 psi when I jumped the yellow clip, but when I try starting it (with jumper properly removed) I only see about 20 psi .
Why do you have an aftermarket FRP anyway? Your mod list doesn't seem to justify one. You don't mention an upgraded pump...
#12
Full Member
Thread Starter
Join Date: Jul 2004
Location: Sacramento
Posts: 164
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by NZConvertible
The FPR solenoid is only activated for hot starts if the ECU sees coolant temp over 140degF and intake temp over 149degF, and only has any effect after starting, because like Hailers said there's not enough vacuum during cranking to bring fuel pressure down. During cranking it should basically see static fuel pressure, i.e. 36-37psi.
Measure the fuel pump voltage while cranking. It sounds like there's an issue with the pump voltage dropping during cranking.
Why do you have an aftermarket FRP anyway? Your mod list doesn't seem to justify one. You don't mention an upgraded pump...
Measure the fuel pump voltage while cranking. It sounds like there's an issue with the pump voltage dropping during cranking.
Why do you have an aftermarket FRP anyway? Your mod list doesn't seem to justify one. You don't mention an upgraded pump...
As far as voltage, I still have to check, but I suspect the pump is getting voltage through the pump resistor rather than a full 12v as is should when cranking. I am going to pull the pin at the ECU that grounds the resistor relay and see if I get proper pressure during start.
As for why I replaced the FPR, in the past I suspected the stock FPR was bad and I had plans for a after market pump and higher boost. Now all I want to do is get it running and sold. I have had it with rotaries..clearly they have it out for me as this is my 2nd 7 with no luck, my other a 1st gen with a 13bt that failed.
I am determined to get it running though..I refuse to sell it without taking it for spin after all my hard work!
#13
I'm a boost creep...
Join Date: Jan 2002
Location: Auckland, New Zealand
Posts: 15,608
Likes: 0
Received 8 Likes
on
8 Posts
Originally Posted by rhythmfunk
As far as voltage, I still have to check, but I suspect the pump is getting voltage through the pump resistor rather than a full 12v as is should when cranking. I am going to pull the pin at the ECU that grounds the resistor relay and see if I get proper pressure during start.
See the FSM pages 4B-72 and 4B-73.
#14
Turbo Waggin
iTrader: (5)
Join Date: Sep 2004
Location: El Segundo Sunny State
Posts: 1,166
Likes: 0
Received 0 Likes
on
0 Posts
Can someone link to a basic write up for electronically retards folks like me.... im trying to fix my cold start issue and think i have stumbled across a good answer in the above posts.... What id like to know is how to either check if there is an "open " in the water thermo sensor wires....
then from there... if it does'nt solve the problem, how to check to PSI of the fuel supply at the rail and wherever else makes sense.... Thanks for any help...Also, i have no upgraded fuel system components... it is a 88 NA with a complete rats nest removal.
then from there... if it does'nt solve the problem, how to check to PSI of the fuel supply at the rail and wherever else makes sense.... Thanks for any help...Also, i have no upgraded fuel system components... it is a 88 NA with a complete rats nest removal.
#15
rotorhead
iTrader: (3)
Here's another question (semi-hijack). I've got an aeromotive FPR with 720/1600 and Supra TT pump. I was planning on setting the fuel pressure by jumpering the fuel pump check connector and turning the adjuster to about 40psi. Is that what it should be at without the car pulling vac? Or is it 37psi? Don't most piston engines run at 43psi?
#16
HAILERS
Join Date: May 2001
Location: FORT WORTH, TEXAS,USA
Posts: 20,563
Likes: 0
Received 21 Likes
on
19 Posts
Can someone link to a basic write up for electronically retards folks like me.... im trying to fix my cold start issue and think i have stumbled across a good answer in the above posts.... What id like to know is how to either check if there is an "open " in the water thermo sensor wires....
then from there... if it does'nt solve the problem, how to check to PSI of the fuel supply at the rail and wherever else makes sense.... Thanks for any help...Also, i have no upgraded fuel system components... it is a 88 NA with a complete rats nest removal.
then from there... if it does'nt solve the problem, how to check to PSI of the fuel supply at the rail and wherever else makes sense.... Thanks for any help...Also, i have no upgraded fuel system components... it is a 88 NA with a complete rats nest removal.
The easiest way is to back probe with a meter, the green/white wire at the ECU with the plug connected to the ECU. Key ON, Meter neg lead on a known gnd. With a hot engine the reading should be a half volt i.e. 0.4 to 0.5vdc. If the engine is cold, the reading might be as high as three volts plus. Monitor that reading with the engine warming up and the reading should decrease continually til the car is hot and the reading is a half volt.
If you INSIST on ohming the thing out, pull the middle plug OFF and read the green/white wire to ground. Meter on ohms. Key OFF. The reading should come close to matching the figures in the FUEL section of the FSM.
I assume this is a series four car.
If you had a RTEK2.0 you could simply look at the displayed water temperature on the Palm and see the coolant temp. No coolan temp........disconnected sensor.
#17
I'm a boost creep...
Join Date: Jan 2002
Location: Auckland, New Zealand
Posts: 15,608
Likes: 0
Received 8 Likes
on
8 Posts
Tee a pressure gauge into the line between the fuel filter and the fuel rail. Jumper the fuel pump check connector, turn the ignition on and read the gauge. Should be 36-37psi.
FC's run 36-37psi. Don't care much about other cars. I assume with a fuel system like that you're not using the stock ECU, so set it at whatever you want and tune accordingly. 40-45psi is fine. If you have a stock ECU you need to run stock fuel pressure or use a fuel controller, otherwise increasing the static fuel pressure will cause constantly rich mixtures.
Here's another question (semi-hijack). I've got an aeromotive FPR with 720/1600 and Supra TT pump. I was planning on setting the fuel pressure by jumpering the fuel pump check connector and turning the adjuster to about 40psi. Is that what it should be at without the car pulling vac? Or is it 37psi? Don't most piston engines run at 43psi?
#18
Turbo Waggin
iTrader: (5)
Join Date: Sep 2004
Location: El Segundo Sunny State
Posts: 1,166
Likes: 0
Received 0 Likes
on
0 Posts
The easiest way is to back probe with a meter, the green/white wire at the ECU with the plug connected to the ECU. Key ON, Meter neg lead on a known gnd. With a hot engine the reading should be a half volt i.e. 0.4 to 0.5vdc. If the engine is cold, the reading might be as high as three volts plus. Monitor that reading with the engine warming up and the reading should decrease continually til the car is hot and the reading is a half volt.
I assume this is a series four car.
I assume this is a series four car.
can i test the sensor itself?
this is the sensor threads into the rear or the t-stat housing? green plug?
#19
Turbo Waggin
iTrader: (5)
Join Date: Sep 2004
Location: El Segundo Sunny State
Posts: 1,166
Likes: 0
Received 0 Likes
on
0 Posts
Update... followed the instructions... ran cold at 3v and as it warmed up it slowly dropped... then settled at .45v... sounds good?
So... if my problem is really hard cold starts.. sometimes needing to spray a bit of starter fluid.... where else should i start looking?
So... if my problem is really hard cold starts.. sometimes needing to spray a bit of starter fluid.... where else should i start looking?
#20
HAILERS
Join Date: May 2001
Location: FORT WORTH, TEXAS,USA
Posts: 20,563
Likes: 0
Received 21 Likes
on
19 Posts
Yeah. That's a normal water thermo sensor. BAC plug connected? It holds to the open positon during START. Adds more air.
Welllllll, there is another possibility. Put that meters positive lead in the backside of pin 3B, a black/blue wire on the ecus' small plug. Bottom row, far right. Connector connected up to the ECU. Put the neg lead of the meter on a known gnd. Like a ECU mounting bolt/stud.
Go to START and see if the meter reads b/t 9 and 12vdc when the key is held to start. Let go of the key and there will be no voltage. IF you did NOT see 12vdc as the key was HELD to START, then that might be the problem. Check that out.
The ECU is looking for that good water thermo sensor signal that you know is good. It's also looking for the Start signal when the key is held to Start. And it's looking for rpm's under 500rpm. No 12vdc on the 3B wire means THAT is the problem. IF that were the case, then the ECU will use the afm signal for fuel amount instead of the MAP inside the ECU that is normally used for Starting fuel.
Welllllll, there is another possibility. Put that meters positive lead in the backside of pin 3B, a black/blue wire on the ecus' small plug. Bottom row, far right. Connector connected up to the ECU. Put the neg lead of the meter on a known gnd. Like a ECU mounting bolt/stud.
Go to START and see if the meter reads b/t 9 and 12vdc when the key is held to start. Let go of the key and there will be no voltage. IF you did NOT see 12vdc as the key was HELD to START, then that might be the problem. Check that out.
The ECU is looking for that good water thermo sensor signal that you know is good. It's also looking for the Start signal when the key is held to Start. And it's looking for rpm's under 500rpm. No 12vdc on the 3B wire means THAT is the problem. IF that were the case, then the ECU will use the afm signal for fuel amount instead of the MAP inside the ECU that is normally used for Starting fuel.
Thread
Thread Starter
Forum
Replies
Last Post
trickster
2nd Generation Specific (1986-1992)
25
07-01-23 04:40 PM