Fuel rail pressure when starting? Real Time Help please... (1 Viewer)

[mabrodis]

Regrading this thread: https://forum.ih8mud.com/showthread.php?t=99905

1996 4Runner, 3.4L V6

Long issue about not starting when warm, can someone, anyone verify what fuel rail pressure they get when cranking the engine, either by disconnecting the coil packs so it won't start or by just kicking the starter a few times so it'll spin but not quite start.

We get 21psi, and am just about ready to go buy a fuel pump...but would GREATLY appreciate any firsthand pressure values...I think any vehicle with the 3.4L V6 would give us valid numbers...

Can anyone check/remember fuel rail pressures?

Thanks a ton!
Mark

 

[mabrodis]

i think that if u got any fuel pressure it should fire
21 sounds like plenty to me

Ok...thanks for the response...normal idling pressure is 32-36 and it's sposeto hit I think 42psi with the pressure regulator disconnected...we haven't seen that though...got a bunch of parts to replace now...

Thanks,
Mark

 

[mabrodis]

Hey thanks for the tips toynado!

Just finishing replacing the fuel rail pressure regulator.

While working on it earlier we thought about the wet plugs, but never saw anything wet, all cylinders getting spark (pulled all and had all plugs out while spinning the engine to watch spark).

The starved/flooded question is a very good one, I think it's starved (when this happens, this only happens when engine hot and has sat for ~20 minutes), when cranking it the engine sputters and wants to start.

It sounds like like a vapor lock situation, but ofcourse with a properly functioning fuel injected system vapor lock isn't sposeto happen, unless the pressure isn't high enough...(i.e. pressure regulator isn't working, which is what we're replacing right now).

Putting the meter on the 12v wire at the pump is a good idea, although I don't think we can easily get to the pump, since I think to even get to the wires (other than find them in the wiring harness at a better location) you might have to drop the tank. We have a fuel pump here so if this doesn't fix it we'll drop the tank and go that route.

Thanks for the help!

 

[Jukelemon]

Do you need that ECT sensor?

By the way, I did that trick with the fuel pump jumper wires, completely took care of my issue.

Here is your answer to your spec question.

http://personal.utulsa.edu/~nathan-buchanan/93fsm/engine/87fuelpump.pdf

Your starting psi's, if your measurements are accurate, are 50% of what it should be regardless of being hot or cold. With the pressure regulator hose disconnected, you should see 38-44psi's at idle. 33-37 at idle with the regulator hooked into the system.

So, that would explain your issue I think. Now what is causing that is a different story BUT the FSM should walk you through it AND that link has the entire FSM on it for both the 22re and the v6. I believe it is the same link as what is in the Facts section.

 

[CJF]

Just finishing replacing the fuel rail pressure regulator.

And???

 

[mabrodis]

And???

And...nothing...no change at all...we started replacing the fuel pump tonight...are in Silverton, CO in a campground, actually in my tent right now on a free wifi...kinda sweet, and it's raining...

But no, it's not the FPR, we think fuel pump and wiring to it, since the actually electrical connector into the fuel pump was badly burned...yes burned/charred and falling apart, we we're splicing in new wires, etc...and we'll see tomorrow how it goes...my guess that fixes everything...

Also I found out from Gadget online (dude that is THE source for supercharger stuff on the 3.4L engine) that Toyota's documents are all wrong about fuel pressure, and it should always, ALWAYS be at 43.5psi, and he's seen dozens of trucks, so I tend to believe him...also he said the disconnecting of the vacuum to the FPR is a bunch of crap, that never does anything on any vehicle, ever (his words, not mine)...

Will post again...

 

[CJF]

And...nothing...no change at all...

Damn!

are in Silverton, CO in a campground, actually in my tent right now on a free wifi...kinda sweet, and it's raining

Watch out for lightning!

Good luck,

Curtis

 

[mabrodis]

Wahoo!!!

After many hours of back breaking work (we are doing this in a campground remember), we got the new fuel pump in with the spliced in wires and all that...and started it up and not only did it start, the fuel gauge we put on the fuel rail showed 42-43psi, it has NEVER shown that high when running. It would appear all symptoms are gone and it was either (or both) the wiring to the fuel pump (forsure) or the pump was drawing too much current and caused the wiring problem, but in either case, it appears to all be fixed...

We did notice another odd thing today, the pressure quickly jumps to 42psi when you crank the engine, which is great, but as soon as you shut it off it immediately drops to zero. Which is actually not right, and it did not do that before (it was at a lower pressure but would hold it for quite some time, and would actually climb to about 40psi with the gas expanding and all that)...so that's frustrating and I think the fuel pressure regulator is sposeto hold that pressure (it's not actually the pump holding that pressure is it?), and the FPR is brand new...so we'll look at that later, but doesn't matter alot since it will start up without alot of problems, sometimes have to push the gas pedal down a bit, but always starts. We contemplated leaving the old pump in there since the wiring looked like the problem, but that would have been stupid, even for us after how much work that was to get the tank out...

Mucho Gracias for all the help...and Silverton, CO is a blast.. .

 

[WristPin]

GOOD NEWS!

i am glad to hear this!
woo hoo!

 

[2ndGenToyotaFan]

Right on man!!! I love it when I figure something out and get it fixed. Congrats!

 

[mabrodis]

Update: The fuel pressure dropping to zero right after shutting it off has ceased. After a few e-mails back and forth to Gadget Online (dude with super knowledge about fuel systems on the 3.4L V6, he installs supercharges on them, etc), he said the pressure is held by a checkvalve on the end of the pump, so if the pressure is not holding (and it's not a injector issue) it's probably that checkvalve. However, after a day of driving the pressure is now holding and the 4runner starts beautifully (i.e. crank it with no gas pedal and it fires right up like it should).

Pressure is solid at 42-43 psi ALL the time.

We have a picture of the burned fuel pump wire that we will post, it makes me a bit uneasy thinking others might have a hot fuel pump wire inside of their fuel tank, not a good place for a hot wire, or something sparking...the annoying part is testing the fuel pump voltage at the tank connector would do no good, since this problem was inside the tank on the short jumper wire from the tank's connector to the actual fuel pump, so you HAD to get in there to see/test that (if you had isolated the pump's pressure you could have verified something was wrong, but still wouldn't have known if it was the pump or the interior wiring until you got in there).

Hopefully this thread will be helpful to someone else sometime...

 

[MonkeyJump]

I seem to have a similar problem. 1996 4Runner V6. It starts fine in the morning but when driven and after a few stops it cranks but won't fire. After replacing my starter(it was going bad anyway) and spark plugs and a dealer that can't diagnose it... My key suspects are the ECT sensor and the fuel pump. So I wanted to ask if replacing the ECT sensor had any effect. I also wanted to ask where that sensor is and what it took to change it. My mechanics manual doesn't show where it is and Toyota parts dealer pretends not to know what I am talking about. I also wanted to ask where the bad wiring was on the fuel pump. Was it outside the tank or inside the tank? Thanks for any help here.

 

[mabrodis]

I seem to have a similar problem. 1996 4Runner V6. It starts fine in the morning but when driven and after a few stops it cranks but won't fire. After replacing my starter(it was going bad anyway) and spark plugs and a dealer that can't diagnose it... My key suspects are the ECT sensor and the fuel pump. So I wanted to ask if replacing the ECT sensor had any effect. I also wanted to ask where that sensor is and what it took to change it. My mechanics manual doesn't show where it is and Toyota parts dealer pretends not to know what I am talking about. I also wanted to ask where the bad wiring was on the fuel pump. Was it outside the tank or inside the tank? Thanks for any help here.

I don't remember anything about the ECT, but the wire that was bad was inside the tank. It was the ~12" long piece that went from the tank connector down to the pump. The plastic connector where it clipped into the pump was partially melted away and the wire had clearly gotten hot and was brittle, missing insulation. We spliced (soldered) a new wire for that part and a new blade-style slide-on connector (if doing this pay attention to which wire goes where on the pump since if you ditch the plastic connector entirely you don't have anything that tells you what wire goes where) onto the pump.

Interesting though as when I wrote this I was doing this work on a friend's '96 4runner, I also have a '96 4runner but mine was fine. Now years later, he has long since sold his and I have had some fuel issues with mine. The last time I had the tank out to replace the fuel pump I did this same mod on my wires going to the fuel pump because I wasn't happy with how weak the electrical connection was to the pump, even though mine wasn't melted but the actual metal contact parts still looked oxidized and did not have much spring left in them. Was it causing the pump to not get enough power? Not sure, but it sucks a$$ to drop that tank repeatedly by yourself (I've done it a few times), so I was doing as much as I could while in there.

Good luck...

 

[Tacoma2002PreRun]

Wahoo!!!

After many hours of back breaking work (we are doing this in a campground remember), we got the new fuel pump in with the spliced in wires and all that...and started it up and not only did it start, the fuel gauge we put on the fuel rail showed 42-43psi, it has NEVER shown that high when running. It would appear all symptoms are gone and it was either (or both) the wiring to the fuel pump (forsure) or the pump was drawing too much current and caused the wiring problem, but in either case, it appears to all be fixed...

We did notice another odd thing today, the pressure quickly jumps to 42psi when you crank the engine, which is great, but as soon as you shut it off it immediately drops to zero. Which is actually not right, and it did not do that before (it was at a lower pressure but would hold it for quite some time, and would actually climb to about 40psi with the gas expanding and all that)...so that's frustrating and I think the fuel pressure regulator is sposeto hold that pressure (it's not actually the pump holding that pressure is it?), and the FPR is brand new...so we'll look at that later, but doesn't matter alot since it will start up without alot of problems, sometimes have to push the gas pedal down a bit, but always starts. We contemplated leaving the old pump in there since the wiring looked like the problem, but that would have been stupid, even for us after how much work that was to get the tank out...

Mucho Gracias for all the help...and Silverton, CO is a blast.. .

Yo, I just wanted to say THANK YOU MAN !! All your work saved me so much time and money. My 2002 Tacoma 3.4 PreRunner had the exact same symptoms for 8 months. Your post was the only one that described the Hot Start problem to a tee. So, I decided to work backwards from your solution. I dropped the tank, replaced the entire fuel pump assembly for 115.00, and bam hot start gone and truck throttle response is so much better, running like a champ. 215K on it. I only had a 2.5 hour tank drop ignorance tax too .. You dah man !!


Bobby in Blanco TX

 

[Tacoma2002PreRun]

Yo, I just wanted to say THANK YOU MAN !! All your work saved me so much time and money. My 2002 Tacoma 3.4 PreRunner had the exact same symptoms for 8 months. Your post was the only one that described the Hot Start problem to a tee. So, I decided to work backwards from your solution. I dropped the tank, replaced the entire fuel pump assembly for 115.00, and bam hot start gone and truck throttle response is so much better, running like a champ. 215K on it. I only had a 2.5 hour tank drop ignorance tax too .. You dah man !!


Bobby in Blanco TX