Popping and a lot of Hesitation When Cold

[LT_Chambers]

Hi all, I'm having some trouble with my 1UZ and I have a idea on what it could be and asked around locally but wanted to get ideas from here as well.

I have a 1995 Era SC400 1UZ-FE in my 1987 Supra. When I start it up cold the engine pops, and if I attempt to drive it, the engine breaks up quite badly very early on in the rpm range. I could maby get 1500 rpms before it breaks up. However the problem does not go away completely after reaching operating temps, when pulling in the upper rpms, 3500 and up, occasionally the engine will break up.

It feels like my friends turbo Supra when he hit fuel cut running a little to much boost. So that leads me to believe maybe the engine has a fuel deficiency when on warm up cycle and at higher rpms. Currently I'm running the original non turbo fuel pump to supply the fuel. Which leads to the question, could the non turbo fuel pump cause this breaking up and popping? Thanks.

 

[BigKriss]

Popping when cold and predominantly through the intake and throttle body is always indicative a very lean afr situation. If your on programmable efi , check out your base maps first, then move on to the cold start and low temp compensation.

If you are on factory efi, I would not have a clue where to start looking for problems !
I would however check components related to the cold starting phase of the management like the auxiliary cold start injector(if fitted, I dont know the Toyota sytem) the water temp sensor,etc.

 

[LT_Chambers]

I'm on the factory efi system, the engines' warm up cycle utilizes all the fuel injectors instead of a loan cold start injector. I purchased a new fuel pump for it, I'm going to install that when I get a chance and with a slight chance of luck it will solve the problem. Thanks for your reply.

 

[BigKriss]

Hi, any positive results yet with the new fuel pump ?

 

[spf_lexus]

How old are the plugs/wires? Do all the problems go away when brought to operating temps?

One thing to consider is the ECT sensor. The motor literally runs off this single sensor until its warmed up and brought into closed loop operation. Maybe try swapping it out for a different one and check for a change.