Weird hesitation during cold start, 1993 FZJ80 (1 Viewer)

[andyquoll]

My 80 has a weird cold start issue, hoping someone can advise. This happens when cold out, like fall temps or colder. Never in summer.

I go to start it, it fires right up for a split second, and then takes a little pause (for lack of a better word) and then revs back up into the cold start zone. (1500 rpm or so.) The pause is short enough that I don't have to engage the starter again, and the cold idle is rock solid after it;s running. If it's really REALLY cold (I live in Steamboat so it can be -20 in the morning) it might stumble for a second during the "pause" before it fully catches.

Any thoughts as to what this is? It seems to get worse the colder it is. Generally if it's 60 or warmer this doesn't happen at all. I've gone through the standard tune up stuff, and the intake hose has no cracks.

 

[RAYJON]

Check connections at fuel filter/change it and the copper washers..you are getting a air gap in the line or the fuel pump is getting old and not pressurizing quick.. You can also pull the cover under the back seat and pull the pump and in tank filter and check them.. pump is Cheep even a Supra pump upgrade is less than 100$..

 

[andyquoll]

Thanks for the response. Would either of those issues give me any other symptoms? Other than this startup issue the truck runs perfect and gets great mileage (for an 80)

 

[enox]

Check connections at fuel filter/change it and the copper washers..you are getting a air gap in the line or the fuel pump is getting old and not pressurizing quick.. You can also pull the cover under the back seat and pull the pump and in tank filter and check them.. pump is Cheep even a Supra pump upgrade is less than 100$..

Can you please elaborate on this supra upgrade..

 

[RAYJON]

Fuel systems can bleed back or loose pressure, so the pump has to fill the system before pressure comes up, cooler weather causes things to contract at the same time you may have a week fuel pump not Pressurizing quickly, try this cycle the key twice then start the truck. This way the pump primes the engine twice and see if the problem goes away.

 

[RAYJON]

Can you please elaborate on this supra upgrade..

[/https://forum.ih8mud.com/threads/supra-fuel-pump.1182186/

it’s not needed and is overkill.. was ment as sarcasm.

 

[andyquoll]

Fuel systems can bleed back or loose pressure, so the pump has to fill the system before pressure comes up, cooler weather causes things to contract at the same time you may have a week fuel pump not Pressurizing quickly, try this cycle the key twice then start the truck. This way the pump primes the engine twice and see if the problem goes away.

So, cycling did nothing to change the issue but I realized without cranking the fuel pump doesn't energize. So I jumpered the diagnostic connection, put the key to on and waited a few seconds. I could hear the pump running and the pressure regulator. Lo and behold two cold mornings in a row and the start is perfect.

So it seems to be the system bleeding off pressure is the culprit? Or is it not supposed to hold pressure? Could this be a leaky pressure regulator? Seems to me a weak pump would have other drivability issues? People tend to report bogging and low power when that is going on.

If air is indeed getting in the system somehow would that not also mean fuel is leaking? (no fuel smell happening...)

 

[RAYJON]

Depends, i have seen it where air would leak in but liquid wouldn’t leak out.. that’s why I recommended checking the copper sealing rings on the fuel filter..

pump should run for a few seconds when you turn on the key, check the fuel pump relay, sounds like you found the issue, even If the regulator let pressure bleed off a little(normal) the fuel pump coming on with the key on should fix that. I would figure out why the pump isn’t kicking on when you turn on the key...

 

[enox]

This thread has caused me to have mild anxiety about the fuel pump, so I ordered one to do as PM.

AFAIK mine is original at 245k mi.

 

[andyquoll]

pump should run for a few seconds when you turn on the key

Ah, I did not know that. If definitely is not switching on. I could hear it from inside the cab when I jumpered it and turned the key to "on." So the relay is the first thing to check?

Thanks for the help!

 

[RAYJON]

This thread has caused me to have mild anxiety about the fuel pump, so I ordered one to do as PM.

AFAIK mine is original at 245k mi.

Your ocd(obsessive crusier disorder) is kicking in..

 

[enox]

Your ocd(obsessive crusier disorder) is kicking in..

So real.

 

[LandLocked93]

FWIW, I don't hear my pump run either when I turn the key to on. That doesn't mean it isn't tho. I noticed it had been replaced at some point (had a 2008 date on it) during PM this past summer. I'm guessing it may run during turn over (cranking) which would make it harder to hear. Takes almost 2 seconds to catch and run.
Surprisingly small pump, not much larger than the windshield washer pump iirc.

 

[andyquoll]

FWIW, I don't hear my pump run either when I turn the key to on. That doesn't mean it isn't tho. I noticed it had been replaced at some point (had a 2008 date on it) during PM this past summer. I'm guessing it may run during turn over (cranking) which would make it harder to hear. Takes almost 2 seconds to catch and run.
Surprisingly small pump, not much larger than the windshield washer pump iirc.

Yeah from what I can tell, the pump should only be energized when the engine is turning over, and this is switched by way of air going through the maf. There is also the fuel pump relay, which controls the voltage going to the pump. It should put out full 12v at startup, and then at some point (probably when the engine is warm enough) switch to reduced voltage at idle for less fuel pressure. The theory in my case is I'm not getting the 12v at startup, although I'm not sure this wouldn't manifest itself in other ways, like stumbling whenever I step on the gas.

I pulled my fpr and the contact is definitely pitted. I was able to file this down a bit, and then got three good cold starts in a row. I thought it was all good, but then got kind of a rougher start this morning when it was 12 degrees. I will replace the fpr since filing the contact is a stopgap measure, but I have a feeling the hunt will continue.

 

[LandLocked93]

I pulled my fpr and the contact is definitely pitted. I was able to file this down a bit, and then got three good cold starts in a row. I thought it was all good, but then got kind of a rougher start this morning when it was 12 degrees. I will replace the fpr since filing the contact is a stopgap measure, but I have a feeling the hunt will continue.

Indeed the pitting is concerning. Be sure to check the relay receptacle contact surfaces too. If there's pitting on the relay contact odds are good it's also pitted the receptacle surfaces. Should be a straightforward fix tho in conjunction with a new relay.

 

[Bosozoku]

Hi, I'm having the same problem, when I start the car and step in the gas it would stumbled and hesitate, if I immediately want to drive the car it would do the same as if in Parking, I need to wait to reach temperature and the stumble/hesitation goes away....

Mine is a 10-93 FZJ80...

 

[LandLocked93]

Hi, I'm having the same problem, when I start the car and step in the gas it would stumbled and hesitate, if I immediately want to drive the car it would do the same as if in Parking, I need to wait to reach temperature and the stumble/hesitation goes away....

Mine is a 10-93 FZJ80...

If it starts and idles ok and only stutters on tip-in (stepping on the gas) until warm I'd guess the pump is to blame. If you replace it and the issue remains, well at least you know the pump is good. If it's a vintage '93 pump, it's due for replacement anyway. Easy to do - access panel under carpet under middle row. I was able to get to it pulling only one seat, but it's a good time pull both and get a good cleaning on the carpets.
Search for pics in pump replacement threads.
Also replace the pump sock (thin-filament pre-filter attached to the input of the pump).
My pump had already been replaced, but the sock was not (who does this ) so half of it was missing - presumably in the fuel filter at the engine.

 

[Bosozoku]

I went and pull the fuel pump and found that the whole assembly was cover in rust, pullet and wire brushed to remove all the rust, the pump change by previous owner but looks like a generic one, them pump sock defenitly not OEM, I also notice alot of dirt inside the tank (wonder if that is causing the problem).

The weird thing is that there are some days its more noticeable than other (the stumble when steping the gas pedal). Not sure if this is related but worth a try. The exhaust pipe has leaks (holes thru the whole system).