1997 1FZFE Hard Start Only when Cold and Occasional P0172 (1 Viewer)

[blbuck88]

Hello All,
I’ve been chasing a rough starting issue on my 1997 US Spec 80 series along with a random P0172 code for weeks now… and I’m pulling my hair out here! Let me explain: I go out to start the 80 early in the morning (truck has sat all night) and when I start it, it fires up but stumbles, hardly runs and stalls. I restart it and similar response. If I apply throttle while it’s trying to start- there’s little to no response (if anything it makes the hesitation worse). After a time or two of trying to get it running, it finally idles on its own and runs but you can’t move it under its own power (put it in “D” or “R” and it will stall out). If I let it warm up to say 170*F or so it’s completely fine and the rest of the day it runs like a champ except an occasional p0172 code. After the truck is warmed up for the day, it will start every time, just as it should for the rest of the day (zero issues) but let it sit overnight and the starting issue returns like a bad dream.

Now about the code. The P0172 code will randomly come on, sometimes 2-3x a day sometimes only once in 3-4 days. ???

After using “search function” and FSM I’ve gotten nowhere. Per my search & FSM I changed both O2 sensors with New Denso units, changed both Engine Temp sensors (dash and ECM with new OEM units) cleaned Mass Air Flow sensor 3x, changed all vacuum lines with OEM units, new OEM TVV, new OEM Fuel Pressure Regulator, new OEM fuel pressure resistor & fuel pressure relay. When I rebuilt the engine (roughly 25k miles ago) I replaced practically everything with OEM parts. I added New OEM fuel injectors, OEM intake tube and a new OEM Toyota engine wire harness. I’ve cleaned the idle air control valve and new PCV. Even a new break booster valve and lines. The truck runs Amazing as soon as it’s warmed up (it’s my daily driver and it’s driver roughly 5k miles per month). I’ve double checked the torque on manifolds and down pipe/ exhaust manifold, even used a “smoker” to look for intake/vacuum leaks, everything seems fine! What am I missing??

At first it seemed to be related to ambient air temperature; if it was cold outside, say mid 30s it would act up but now it’s upper 80s in the morning when I go to start it and same issue.

Any suggestions? What am I missing?
Thanks!!
Cheers

 

[Malleus]

 

[Malleus]

If the problem was just as bad warm and cold, I'd lean toward a bad, or clogged, Fuel Pressure Regulator. Since it only happens when cold, my first guess would be the Idle Air Control Valve. Failing that, I'd work through the symptom matrix above.

That would be without all the new stuff and work you've done. The only thing you haven't listed are the ECM terminal values checks. That would be my best guess at this point.

 

[blbuck88]

Ok- the idle air control valve makes sense with the hard/rough start and I’d assume it could have an affect on my pesky p0172 code randomly throughout the day. I’ll order a new OEM one and see if that helps.

 

[blbuck88]

Update:
I went ahead and replaced the idle air control valve along with a new idle air control valve O ring with new OEM units. I also removed and cleaned the throttle body, inspecting all ports making sure nothing was clogged, replaced the throttle body gasket and torqued to spec. Next, I reset the ECM by unplugging the battery for roughly 12 hours (I prefer the battery disconnect way VS the efi fuse way: idk why). The result- Absolutely No Change…. I’ve driven it for the past week and It’s still hard to start in the morning, takes 2-3 times of starting and stalling for it to finally stay running and occasional P0172 code. I double checked the timing (with the jumper plug as per FSM) and looked over all vacuum lines. Everything seems in order.

Question: could a clogged catalytic converter be my issue? Here’s my hypothesis: old clogged catalytic converter takes some heat/ temperature to do it’s job (hence, once it’s warmed up it functions properly). Thus, causing issues with starting until it’s up to operating temp? After it’s warm, it starts and idles great (but I still get the random p0172 code?)

Second: less likely but I’ve noticed when I put fuel in the tank, a tremendous amount of pressure is released when I unscrew the fuel
Cap, signifying I have a clogged charcoal canister. Could this pressure be giving me issues?

Last: fuel pump going out??

Thoughts??

 

[LongDuck]

Here's a somewhat random thought, but you've already covered the immediate things; your comment above about the fuel pressurization in the tank has me curious if you've got some kind of problem with the tank venting purge system.

Here's my thinking - under the upper intake manifold on the DS is a solenoid valve which allows fuel tank pressure to vent into the charcoal canister. If this valve gets blocked, it will allow your fuel tank to preasurize to the point that when you open the filler, liquid gas will spray out at you with a full tank. A negative consequence is that your fuel tank becomes a pressure vessel and expands and contracts, exposing the weak spot in the metal structure on the top where the parking brake cable leads. This creates an oil can dent which cracks, and leaks fuel when the tank is more than 80% full or on an incline. I know this, because my 80 ate 2 fuel tanks before we figured out it was the vent solenoid valve up near the firewall.

I'm guessing that when it sits overnight, the tank cools which leads to a vacuum compared to the previous day, and the fuel pump is trying to suck fuel against a vacuum, leading to low or nonexistent fuel pressure at the rail. When you crank it, the pump has more time to strain, eventually getting enough fuel pressure to the rail for the fuel injectors to spray and ignite. Once your engine is running, the fuel tank pressure increases, helping the pump to do it's job, and you're good for the day.

Quick test; try cold starting it with the fuel cap removed and see if that changes anything. This may remove the vacuum from the tank, so listen for a pop or hiss when the cap comes off, even though it's cold. See if it starts right up, as we've removed the vacuum restriction from the pump by venting the tank to atmosphere.

Added; P0172 is overly rich - this might be fuel injector leak-down, or low fuel rail pressure which means the injectors aren't spraying, theyre dripping. Also, check and clean MAF sensor between the air filter and intake. Have you run any fuel injector cleaner ever?

Oh, and pull the dipstick and see if it smells like gasoline.

 

[blbuck88]

Thanks for the reply, I think you are onto something here LongDuck. When I removed the gas cap to refuel the truck earlier today, I paid close attention to the pressure as I removed the cap. There was enough pressure that once the cap was removed, I could see droplets of fuel spraying out from the fill neck. I noticed my hand actually gets a decent amount of fuel spray on it simply unscrewing the cap for removal. I’ll test this fuel pressure theory over the next few days and report back.

As for the p0172 code; I replaced all 6 injectors when I rebuilt the engine, along with plugs, fuel filter, fuel pressure regulator, fuel relay and resistor with all new OEM units. I also replaced the rubber intake tube, and cleaned the MAF several times. Maybe there’s an issue with one of the new injectors? Or possibly the fuel pump is providing intermittent pressure (not consistent) and thus throwing off the fuel map???? I’ve noticed I only get the code when I’m coming to a stop or slowing down. Never under acceleration or when at steady speeds (I drove it 380 miles today on the interstate and it never came on until I pulled off the freeway, slowed down and came to an intersection). I’m baffled. ???

Thank You for helping, much appreciated!

 

[blbuck88]

Bump - Update:

I’m still struggling with this stupid hard start when cold, p0172 code. Since my last post here’s what I’ve done:

-changed out the charcoal canister with a Duralast VC120 (AutoZone) unit. No effect on the hard start issue or my code But I’m very pleased to say I no longer get sprayed with fuel when I go to remove the fuel cap

-next I replaced the fuel pump, along with sock, pump cushion, tank gasket, etc with a new Denso unit. All I noticed from this change was a little smoother idle and the reassurance the old pump wasn’t going to take a crap on me leaving me stranded in the middle of nowhere.

-I did another smoke test to the exhaust and found 2 very small holes in the gaskets between the cats. So, I replaced both gaskets with OEM units, replaced the hardware and tack welded a few spots on the muffler that looked like they were leaking at some point. Zero change….

-finally I went ahead and exchanged the MAF sensor with an OEM eBay special from an 80 that had roughly 140k miles. And the result is the same, no change to hard start/p0172 code but now I’ve also gotten a p0130 & p0133 code a few times!!

Any thoughts on what to do next? Aside from doing another smoke test on the vacuum lines to see if I missed a vacuum leak last time (I’ll perform this tomorrow evening regardless). I’m running out of things to check and replace!!

 

[Malleus]

Since the only thing you haven't listed is the ECM terminal check, I'd look there.

 

[blbuck88]

Ok- so it sounds like you think the issue might be in the ECM?

 

[gripguru]

Bump - Update:

I’m still struggling with this stupid hard start when cold, p0172 code. Since my last post here’s what I’ve done:

-changed out the charcoal canister with a Duralast VC120 (AutoZone) unit. No effect on the hard start issue or my code But I’m very pleased to say I no longer get sprayed with fuel when I go to remove the fuel cap

-next I replaced the fuel pump, along with sock, pump cushion, tank gasket, etc with a new Denso unit. All I noticed from this change was a little smoother idle and the reassurance the old pump wasn’t going to take a crap on me leaving me stranded in the middle of nowhere.

-I did another smoke test to the exhaust and found 2 very small holes in the gaskets between the cats. So, I replaced both gaskets with OEM units, replaced the hardware and tack welded a few spots on the muffler that looked like they were leaking at some point. Zero change….

-finally I went ahead and exchanged the MAF sensor with an OEM eBay special from an 80 that had roughly 140k miles. And the result is the same, no change to hard start/p0172 code but now I’ve also gotten a p0130 & p0133 code a few times!!

Any thoughts on what to do next? Aside from doing another smoke test on the vacuum lines to see if I missed a vacuum leak last time (I’ll perform this tomorrow evening regardless). I’m running out of things to check and replace!!

Did you ever resolve your issue? I’m have cold start issues, but have no codes.

 

[blbuck88]

Update- Issue Resolved:

After replacing and checking multiple different items (see thread for full list) I decided to send my old “original” fuel injectors to to have them professionally cleaned and swap them with the new Denso ones I bought from ebay when I rebuilt the engine. I believe I used InjectorRX in Texas and after a week or so I received the reconditioned injectors with the paperwork showing before and after results.

I was able to swap the injectors without removing the upper intake (I removed the throttle body assembly and slid the injector rail out along with the injectors) then reinstalled the reconditioned injectors with OEM gaskets, reset the ECM (battery disconnect overnight) and Problem Solved! It starts just like it should regardless of temperature and no more code! Beware of buying Denso injectors from eBay! Although they arrived in OEM Toyota boxes, upon closer inspection I believe they are knockoffs.