Fuel Pressure.

[vponomar]

Hi guys. I have noticed a fuel pressure drop after my 91T with 170 kmiles sits overnight in the garage or even after few hours after stop. It takes time to build fuel pressure again and to crank her. Question: what is the most likely cause of the pressure drop? I have switched to AFPR, but it didn't help. What is my next bet?
Thanks.

Vlad.

 

[jetjock]

Some loss in that time is completely normal. If it falls within Toyota's test limits (see the TSRM) it's OK.

That said loss of rest pressure (Toyota calls it residual pressure but I prefer the Bosch term) can be from external or internal leakage. External leakage is self explanatory. Internal can be anything upstream of the fuel regulator on the pressure side of the system. For example injectors (including the CSI), check valve in the pump, or the regulator itself. In other words anything that allows leakage into the engine, into the return line, back into the tank, or into the outside world.

The fuel pump in this car doesn't run until the key is held to start. If you want priming prior to that as many cars have there are a few things you can do to get it. None of them should be necessary however. If you're having hard starts you should look elsewhere

 

[vponomar]

Some loss in that time is completely normal. If it falls within Toyota's test limits (see the TSRM) it's OK.

That said loss of rest pressure (Toyota calls it residual pressure but I prefer the Bosch term) can be from external or internal leakage. External leakage is self explanatory. Internal can be anything upstream of the fuel regulator on the pressure side of the system. For example injectors (including the CSI), check valve in the pump, or the regulator itself. In other words anything that allows leakage into the engine, into the return line, back into the tank, or into the outside world.

The fuel pump in this car doesn't run until the key is held to start. If you want priming prior to that as many cars have there are a few things you can do to get it. None of them should be necessary however. If you're having hard starts you should look elsewhere

Thank you. So, where should I look for hard starts?

Vlad.

 

[Reaper Man]

Thank you. So, where should I look for hard starts?

Vlad.

I could be wrong, but I think alternator

 

[bmoss85]

my car was doing somethng similar and it ended up being the cold start injector

 

[vponomar]

my car was doing somethng similar and it ended up being the cold start injector

How did you find it out? Does anybody sell them (cold start injectors)?

Vlad.

 

[bmoss85]

my check engine light came on and i eventually found a broken wire going to the temp sensor for it. my car would take forever to star until i found what it was, it would run fine once i got it started. it hasnt been a problem since the fix though.

 

[jetjock]

^ That doesn't make any sense because no part of cold start system is monitored by the TCCS in any way but hey, whatever works. I'm guessing it was your EFI coolant sensor wire that was busted. That'd cause it.

Vlad: First determine if the loss of rest pressure is within limits. If it's not it'll only effect hot starts. You didn't say whether the hard starts were cold or hot. If you're having hard cold starts the problem could be the CSI or thermo-time switch. It could also be a bunch of other things. Before the next start build pressure in the fuel system first by jumpering B+ and FP in the diagnostic block and see if that helps. At least that'll tell you if the problem is fuel pressure related.

A leaking CSI could also be causing a loss of rest pressure outside the specified limits. Either pull it out or look though the throttle body with a flashlight to see if it's leaking. Again, do that with B+ and Fp jumpered. On the opposite end of the spectrum they tend to get gunked up and not work at all. Clean it. Don't buy a new one unless you have to. Anyways, check the rest spec first. It escapes me at the moment. The numbers 21 psi after 10 minutes come to mind but I could be wrong. What I do know is a good fuel system will hold rest for much longer than what Toyota specifys.

 

[bmoss85]

im just saying what toyota told me when i called and asked them what the code was for. my car has started fine ever since

 

[cuel]

http://cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=FI&P=73

21 psi or more for 5 mins. Thanks Jet, I was needing that info and forgot until you mentioned it.

 

[Poodles]

the EGR port comes out right in front of the CSI...

my CSI was DOUBLE it's usual thickness in carbon when I pulled it out. Soaked it in carb cleaner until the carbon dissolved off of it and it's been fine since...

A tired battery and the battery cables can also cause hard starts, along with the starter...

 

[vponomar]

Thank you guys. I'll take a look at CSI and wiring. Should I connect B+Fp with a piece of regular wire?

Vlad.

 

[Mr. Sinister]

Thank you guys. I'll take a look at CSI and wiring. Should I connect B+Fp with a piece of regular wire?

Vlad.

Yeah. A small paperclip would also work.