Longer crank after knock sensor/new injector install

[Noshirtganshirt]

Long story short. Knock sensor or harness went bad last week. Order OEM sensors and harness. Swapped them in. Purchased 6 brand new injectors (OEM brand). Made sure that they all were seated properly before buttoning everything else up.

Fast forward. Car is running great. No misfires, full power (trd Supercharged, stock pulley), and do not smell of fuel.

On a cold start, the car cranks normally and fires up right away. When the car is warm and sits for 15 mins and go to start again. If cranks longer (sputters like it’s getting fuel and then finally fires up.

Pulled the EFI fuse for 30 minutes and then disconnected the battery. Still getting the same symptom.

All vacuum hoses are double checked. Car was firing perfectly before installing new injectors, I just figured I would install new ones while I was down there.

Any ideas?

 

[LittleCaesar]

I'd say to start with your grounds. Can you check fuel pressure to see if it is instantaneous?

How much did that hurt your wallet btw?

 

[thecole1098]

Kinda sounds like fuel pump.

 

[Noshirtganshirt]

I'd say to start with your grounds. Can you check fuel pressure to see if it is instantaneous?

How much did that hurt your wallet btw?

Idk where’d I’d hook into the fuel system to check pressure

Really wasn’t bad for the job. I did the work myself. Both knock sensors and the harness were almost $100 for OEM on eBay. Lower intake manifold gasket was 80$ (cane with upper abs lower gaskets), and new injectors (not needed necesssrily) were 140$ on Amazon (OEM brand).

Kinda sounds like fuel pump.

If it was the fuel pump why is it only long cranking when the car is warm?

 

[thecole1098]

Idk where’d I’d hook into the fuel system to check pressure

Really wasn’t bad for the job. I did the work myself. Both knock sensors and the harness were almost $100 for OEM on eBay. Lower intake manifold gasket was 80$ (cane with upper abs lower gaskets), and new injectors (not needed necesssrily) were 140$ on Amazon (OEM brand).



If it was the fuel pump why is it only long cranking when the car is warm?

This is a known issue with these rigs with age. The valve that is supposed to retain fuel pressure in the rails wears out over time and allows that pressure to drain off almost immediately after running it when hot, hence the extended cranking after the rig has warmed up and the stuttering as it cranks over.

It could also be just something as simple as the fuel filter needing to be replaced.

I'd say to start with checking your fuel pressure while running and watch the gauge after it turns off. It should hold 38-44psi for quite some time before it starts dropping. This test will tell you a lot. If the number is low overall, it's likely a clog in the system, such as the fuel filter.

 

[Noshirtganshirt]

This is a known issue with these rigs with age. The valve that is supposed to retain fuel pressure in the rails wears out over time and allows that pressure to drain off almost immediately after running it when hot, hence the extended cranking after the rig has warmed up and the stuttering as it cranks over.

It could also be just something as simple as the fuel filter needing to be replaced.

I'd say to start with checking your fuel pressure while running and watch the gauge after it turns off. It should hold 38-44psi for quite some time before it starts dropping. This test will tell you a lot. If the number is low overall, it's likely a clog in the system, such as the fuel filter.

Never heard of that valve wearing out. Is that a replaceable part and which valve are you referring to?

Fuel filter is not too old, probably a year old.

Where’s the best place on these to hook up a pressure gauge for the fuel system?

 

[thecole1098]

Never heard of that valve wearing out. Is that a replaceable part and which valve are you referring to?

Fuel filter is not too old, probably a year old.

Where’s the best place on these to hook up a pressure gauge for the fuel system?

No, it's part of the fuel pump unfortunately. On these engines, there's no quick connect fitting so you'll have to disconnect the fuel supply line on the drivers side in the engine compartment and hook the gauge up to that. That's where I've always done it, but there is other areas to connect it, but typically they are harder to get to

 

[Noshirtganshirt]

I’m wondering if it might be a bad fuel pressure regulator.

Still pretty stumped being as the car runs great, no misses, and fires up perfectly when cold starting

 

[19963.4lsr5]

I think you have a injector that is leaking and flooding the engine when hot. You don't notice a dripping injector cold because it's evaporated or ran down into the oil.

If the check valve in the fuel pump is bad a few key on cycles before you tag the starter will prime the fuel rail.

A lot of people here say to check fuel pressure. Not a single one has ever tried to figure out the fittings necessary to check it. If someone actually has the adapters to put in the fuel line at the valve cover post it up.


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[fixxor]

I have had this problem since I swapped my motor. I put in two new OEM injectors and had the rest reflowed at Napa. New o-rings when I installed them. Replaced the fuel pump and still same issue. Going to do the Big 3 wiring upgrade this weekend hoping thats it.

 

[enapa]

I had the exact same symptoms. Replaced fuel pump. No change. IAC valve. No change. Fuel pressure regulator. No change.

Found a leaky injector. Solved.

One tip that I can give you is this. I only found the leaky injector by luck. I had just turned the truck off after driving it and I was pissed and in a hurry so I started tearing down the intake manifold while everything was hot. At this point I had done this about 6 times in a matter of a week or so. So I had it down pretty well. Once I removed the upper plenum I could actually hear the injector leaking.

Note that stuff will be fairly warm, especially the IM bolts/nuts so be careful. But I would put money on a leaky injector and this is the easiest way to confirm.

 

[LittleCaesar]

I think you have a injector that is leaking and flooding the engine when hot. You don't notice a dripping injector cold because it's evaporated or ran down into the oil.

If the check valve in the fuel pump is bad a few key on cycles before you tag the starter will prime the fuel rail.

A lot of people here say to check fuel pressure. Not a single one has ever tried to figure out the fittings necessary to check it. If someone actually has the adapters to put in the fuel line at the valve cover post it up.


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The connector with the little red cap on it is the connector needed to thread into the fuel rail in the front, then use the valve to connect to the gauge.

https://www.amazon.com/Actron-CP7838-Professional-Pressure-Tester/dp/B0009XQUKC

 

[JayRolla]

So you pulled good oem injectors and installed used oem injectors? If you got them new for $140 for all 6 they are most likely knockoffs. Many crappy injectors sold as oem brand but the price is a bit low to be true.

I suspect injector issue maybe.

 

[Noshirtganshirt]

So you pulled good oem injectors and installed used oem injectors? If you got them new for $140 for all 6 they are most likely knockoffs. Many crappy injectors sold as oem brand but the price is a bit low to be true.

I suspect injector issue maybe.

Pulled working OEM injectors and bought new OEM injectors. Thought the price was a little suspect, but they look exactly like the OEM ones that I pulled out.

Ended up having the old OEM ones cleaned and tested by a local shop. All checked out. Just swapped them in. I will check in tomorrow with my results and hopefully solved issue.

Sending the “new” injectors back to amazon next week