Fuel Pressure issues? Intermittently runs rough, no starts, and then ok

2000 toyota tundra 4.7L I think I have a fuel pressure problem. I have a pressure gauge on it and it reads zero with the key turned on. Reads a steady 25 psi at idle and at 60 mph. When I pulled the fuel pressure relay and jumped the terminals I got 25 psi and 35 psi. Presumably I jumped the hi and low pressure circuits. When I apply 12V to 85 and 86 on the relay it clicks so it seems like its working...Shouldn't I get fuel pressure when engine is not running but the key is turned on? Shouldn't it increase to 35 psi at 60 mph?

(My real problem is it runs rough intermittently and even has no start episodes.)

 

No. More info on that over here.

https://www.tundras.com/threads/2006-crank-no-start.112930/#post-2913141

On the rough idle, can be any number of things. But typically speaking, it's from using non-OEM parts for MAF/O2/spark plugs/injectors for example, accidentally getting counterfeit parts off scAmazon/fleaBay/WalMart online because those places are known to sell 'em, vacuum issues, or leaks, like manifold, or electrical like internally corroded battery cables, failing alternator, or other corrosion problems.

Are you getting any codes?

When was the last time you reset the ECU or had the battery unhooked for more than 5-10 minutes? (latter resets the ECU and often causes running like shit until ECU re-learns).

What maintenance have you done prior to the truck running like ass?

 

Oh and gotta ask:
Do you live in an area where rodents are known to nest up in stuff?
Do you live in the a salt/rust belt area, where metal corrosion is an issue?

I only ask because apparently a lot of the wiring and plastic tubing, like on fuel lines, used soy-based plastics which rodents go bonkers over.

 

Parts generally from Auto zone or advance...Rodents and Rust - Yes

The Long Version

This started as I was driving down the highway about 75 mph for about 45 mins and then started to misfire but would run ok at 60...then 50...then died. Wouldn't start towed it home and it started the next morning but ran rough. Had random misfire codes, and misfire codes 1,3,5,7. Lean bank one. At times it would run rough and I could get up to speed then the CEL would start flashing ( too much Oxygen going by the O2 sensor?) so I'd shut it right down

Replaced upstream bank one O2 sensor, ran a little better but then deteriorated and started misfiring
Moved bank one coils around..replaced one that seemed bad...didn't really help
Replaced all the plugs to no effect - still ran rough
Replaced a few vacuum hoses to no effect
Cleaned the MAF sensor with MAF cleaner - Lo and behold she ran like a champ! Took it out on 3 or 5 ten mile loops that week, it ran great. I let it idle in the driveway for about 15 minutes and it stalled. Started it up and she ran rough again. Next day it wouldn't even start.
A few days later I started it with either and it ran idled nice and smooth but stalled as soon as the either ran out. This was when I really suspected a fuel problem.
Replaced fuel filter to no effect.
Continued to try starting it...finally started about 10 days latwer...ran rough and stalled a few times then magically it cleared up and started to run clean again.
So with her running again I put the fuel pressure gauge and that brings me back to the beginning thread....

So when I turn the key to start but not all the way to ignition the fuel pump isn't supposed to go on? When I turn to key to crank the fuel pressure goes to 25 psi, is this correct or should it be up to 38-44 psi? Even at 55-60 mph and 25 psi it ran with out missing...

I'm going to let it idle till it dies tomorrow and see what the fuel pressures are when running rough or no start. (when ever it was running good, idling for 15 minutes seemed to kill it)

 

Could be an issue.

Usually means misfire on at least one cylinder. Flashing because damage to catalytic converter can happen.

What brand? This is where a denso part is very important. If you're replacing one it's best to do all of them if you can.

Fuel pump goes on while cranking, if engine starts it keeps running if it doesn't start it shuts back off. Pump will not prime when you turn ignition on.
As far as fuel pressure I'm not sure.

Plugs from local auto parts store are better than anything from Amazon due to counterfeit at least. What plugs did you get?

While unlikely it wouldn't hurt to switch bank 1 coils randomly with bank 2 and see if anything changes if you run out of other ideas.

Some of this is out of order but I answered what I could anyway.

 

Your longer explanation makes it sound like the ECU is really trying hard to balance out the air/fuel ratio. That can be due to a number of things, like: Inability to see how much air is coming in (failing MAF), inability to control air input (throttle body), inability to push enough fuel (fuel pump), or inability to read the combustion mixture (pre-cat O2).

I'm leaving spark out of that list because I have a gut feeling this isn't related to plugs or coils, but if you bought plugs off scAmazon and replaced them within the last 10k-20k miles, you should really pull a few and check them to make sure they're OK, if they were branded Iridium, make sure the tip isn't melted, which happens on the fakes.

I would just add:

Swapping pre-cat O2 sensors, plugs, or coil packs between bank 1 and 2 to see if a difference happens is worthwhile to see if things follow, if you don't manage to solve this through other means.

You should ideally replace both O2 sensors on a single bank if one in that bank fails; and typically want to use Denso parts here.

If MAF cleaning helped almost immediately after, it may be time to replace with a Denso (Hitachi is also fine) MAF; it's a cheap part to throw at this.

Beware, you can foul your cats in your current shape, which gets spendy.

FSM may actually give PSI levels for fuel on your truck; I doubt this is actually a fuel pump issue, not enough to convince me. Both banks would've been lean IMHO.

 

Thanks guys

Plugs were from advance or AZ...I forget the brand...not the cheapest ones, not the most expensive.

Forgot to mention I did reclean the MAF sensor after it started running rough again...had no effect the 2nd time around.

The new O2 sensor was a Denso. I didn't think the downstream O2 sensor affected how the engine would run, only how the cats were performing?

Let it idle this AM...started to run rough, threw misfire codes for 3,5,6, and 7. Shut it off and cycled the key a few times (saw that on some youtube video) Started it up and it ran fine.

Maybe time to switch coils and o2 sensors around to see if codes follow...

Do you guys trust Rock Auto or Amazon for Denso parts?

 

As long as they're compatible and you gapped them right, that's the biggie - IF they require gapping - some plugs like Iridiums, explicitly tell you not to gap. I never trust pre-gapping otherwise. Different cylinder configurations and different years use different plugs. I normally go NGK, but bought Denso this last go-round.

Maybe it gave up the ghost. I'd replace it with a Hitachi unit if it's still the original. Consider it proactive maintenance. At worst, you're good for another 100-150k. At best, it solves the problem. The intake and exhaust sensors are probably the absolute most critical on an EFI engine, they basically provide much of the feedback needed to understand how efficiently it's managing combustion. There's an argument to be made for knock/cam sensors too, but without intake/exhaust sensors, that engine isn't running long enough to make a diff.

Upstream measures the output of combustion to determine if reach or lean etc. Downstream measures the output of combustion post-cat to figure out how effective the cat is as you say. While I don't always do it, a lot of people will tell you to replace both on the same bank if one fails. If nothing else, you're busting knuckles one day instead of two.

Interesting, I'm surprised to see something on 6 now.

I'm not sure I'd bother with the coils, really, unless you're gung-ho or bored. I'd be shocked to see more than 2 coils went out at once. Just one going out is shocking, two would be a go-buy-lottery-ticket event.

Never buy auto or appliance parts on scAmazon. Too many people on here ended up with counterfeits because of how scAmazon receives, stocks, and distributes inventory for all merchants who fulfill through scAmazon and don't adequately check incoming inventory for fraud. Same goes for fleaBay and WallyMart, who allow unknown entities to sell through their storefronts, they can't/don't authenticate inventory.

Use RockAuto, Summit Racing, etc. if you can wait for it to ship. But if you have an Advance Auto Parts near you, there's virtually always a 10%-25% discount code for their store on RetailMeNot and similar coupon sites, add that to their already-competitive store prices, and immediate store pickup, it's a compelling option.

Sometimes AutoZone has percent-off coupons too, I never find much for Pep Boys or O'reillys, or however you spell it. PB used to be a go-to for me bitd, I think I've walked out of O'reillys empty-handed every time, unable to find what I need. I legitimately don't know how that chain stays in business.

 

Service manual specs 38-44psi, it should also not drop back to 0 when you shut it off. It should hold some pressure for quite awhile after the key is off.

Before you replace the pump though I'd jump the fuel pump resistor and see if you get full pressure that way.

 

I jumped it at the fuel pump relay and got 35 psi so I'm trying to find what tells the fuel pump to run at hi speed. Driving it yesterday I noticed it would tend to miss some when going up around 60, though not enough to throw a code. Also thinking about pulling the relay and jumping the fuel pump to high. If it still misfires I think that will tell me I have more than one problem.

I think shifty is right when he says sounds like ECU is trying to balance fuel and air.....

 

If true, there's not a ton of things that can cause that condition, and most are pointed out above.

I'd still start with tossing in a Hitachi MAF. I don't know as much about the earlier models using throttle cables vs. my dbw so I can't speak to what to check on the TB assembly. Failing pumps can die a slow death where they intermittently pump low but the ones I've had fail over the years were either a slow-death or instant-death situation. I've seen other guys deal with variable-output failure as the pump is struggling to keep up in certain situations.

Still no codes, though?

 

There's also two paths through the relay, one that will run through the resistor and the other goes directly to the pump bypassing it.

It's all controlled through the ECM so you should be getting 38+psi while cranking since it bypasses the resistor in start.

Here's the FSM page about the circuit.

 

Thanks for that diagram Festerw. Looking at that diagram, tell me if this could be the problem, T2 is not closing or the wire from FPR to the relay is bad and not opening the fuel pressure relay to bypass the resistor to give the fuel pump 12V and into high speed. EDIT or not getting the signal from the crankshaft position sensor...

The fuel pressure gauge always read 25 psi on start or engine under load, I only got 35 psi when removed the relay and jumped terminals. If the relay was bad the pump would alway be on high speed and 35 psi?

 

That diagram is awesome. I didn't realize the crank position sensor played a role in the function of the fuel pump, but it makes sense why they'd do things that way considering the way the pump acts for each key position. Unless I'm reading the diagram wrong.

@partschanger actually, I suck at reading diagrams, but it looks to me like the switch enabling toggle between T1/T2 is centered on the fuel pump relay and its input from the ECU. If T1 active, FP relay supplies low power to FP. If T2 lights up, FP relay toggles direct battery power 12v to FP. Have you tested or replaced the FP relay?

Edit: I don't fully understand the purpose of the "EFI Maing" relay or the "Circuit Open Relay" necessarily, but must assume those are working if (A) you can get full 12V direct power to the relay for the former, and (B) you get function out of the FP due to the latter.

 

PS - the video linked here just helped me visualize the layout and make more sense of the wiring diagram.

 

Shouldn't matter which speed at idle. Both would be sufficient to provide enough fuel for that, I'd expect if what you're suggesting happened I'd expect it to be a repeatable issue every time not just intermittently.

It's really starting to sound like the pump itself is dying, engine off, with the relay jumped it shouldn't have any issue hitting the high side of recommended pressure even running through the resistor. Coupled with the fact it sometimes will and sometimes won't start is exactly how every fuel pump I've ever replaced has acted.

 

So lo speed isnt designed to run at lower pressure, the system is designed to run at 38-44 psi all the time. Low and High speed is a volume thing? I should read the pressure with the relay jumped to high at speed. If it can't maintain pressure I should change the fuel pump.

 

Correct, the pressure regulator doesn't really do much to control the pump electrically. It will basically just dump excess fuel into the return line back to the tank.

 

I had a serious issue I chased for a while, computer was telling me bank 1 o2 sensor along with misfires I think. After replacing many parts it turned out to be the hose from fuel pump to sending unit had slipped halfway off. I’m thinking someone may have been siphoning gas from my truck and pushed on it with the siphon hose?

 

It's really starting to sound like the pump itself is dying, engine off, with the relay jumped it shouldn't have any issue hitting the high side of recommended pressure even running through the resistor. Coupled with the fact it sometimes will and sometimes won't start is exactly how every fuel pump I've ever replaced has acted.[/QUOTE]

 

I was also having hard start, extra long key turn, sometimes a few tries

 

Not that it's necessarily important, but did you mention how many miles are on it?

I'm asking that, knowing I had a fuel pump go out on a '98 GM with under 90k miles on the clock. I've been told many times there are manufacturers who design their fuel systems with pumps immersed in fuel to use it as a cooling agent.

The rumour I've heard numerous times in shops and on forums is, for those vehicles, if you run the tank low all the time, like you constantly run it down to 1/8 tank or less before filling up, the pump is allowed to run hot and will fatigue early.

Do I believe it? I'm not sure, but I've also bought custom fuel cells for LS swaps I've done, where the manufacturer intentionally included a baffled area where the fuel pump sits in which is designed to help keep it immersed in fuel (or so the claim was made).

 

Festerw -That made sense to me so I thought I could jump the relay to high speed and take the truck out for a high speed/load with the pressure gauge on expected the pressure to be low confirming the pump was on its way out. I first started her up with the relay and confirmed the fuel pump was still giving low pressure. I jumped the relay to high, see pic, got upper 30's fuel pressure at idle and took it out on the road for about 15 miles. Fuel pressure went up to 40, stayed there, ran well no missing, no codes. So it seemed the fuel pump wasn't terrible. I pulled the vacuum hose off the pressure regulator thinking that could be the culprit....no change in fuel pressure, couldn't feel any vacuum at all when I put my finger over the hose, and that was with pump on hi and low. Could low or no vacuum be the culprit or is the fuel pump still a suspect? My understanding is at idle the vacuum is high and opens the pressure regulator to allow more flow at the lower pump speed. I tried to follow the vacuum line that comes off the regulator but lost it, it seems to go back to the fuel tank.

 

Shifty - about 415 thousand miles.

 

If it's never been done, swap the fuel pump. The OEM pump has done at least 1.5x a "good" lifetime at this point.

Even if it's not 100% the problem, it's a possible candidate, and it's long as hell overdue. But I'd urge you to just drop the $50-100 to do the MAF too.

Reset the ECU after (leave batt neg cable off 10min) and expect to possible run like ass the first dozen or three miles after. ECU will re-calibrate.

At least doing this, as your name suggests "partschanger", you're ruling out one highly probable suspect. MAF would be the other one, this is an EFI engine after all.

 

I’ve got a brand new fuel pump I didn’t need and screwed up on the return I’d sell for $100
Delphi fe0410

 

Stay tuned....I carelessly left the fuel return line off the pressure regulator and started her up...nothing came out of the FPR.....its in the mail. Should be here monday

 

Maybe it’s the fuel pressure regulator itself

 

Oooh, the plot thickens...

 

I hope so. But I have my doubts since the fuel pressure is only 25-30 psi when the pump is on low speed...and doesn't get kicked up to 40 psi unless I jump the relay. ( I tested the relay and it rings out like it should.