Nailit69

So I decided to build my own exhaust since I haven't worked in 2 weeks and have ever dwindling funds. It turned out pretty sweet, sounds really good at idle, a little loud while driving though... I might have to find a way to quiet it down.

The last big problem i'm having is with a sticky/clogged/bad injector. I timed it w/the jumper in the diagnostic and it starts and idles w/no problems but it's still stumbling when I step on it. Otherwise, If i'm real easy on the throttle and keep the RPMs up a little it will do ok and run smooth.

I pulled all the plugs and three of four are burning perfectly and one isn't, looks pretty dark, it's got spark so the plug is obviously working. I can also hear what I think is that injector knocking, it sounds like a valvetrain knock. I put an ear on it and it's not the valves, I can hear it loudest on the intake side if I put my ear next to the plemum.

Will some good injector cleaner remedy the problem or do I need to pull it and swap it or have it serviced? I do have an injector from my old motor that I could try but didn't want to take it apart if I don't have to. Anyone have a clue what could be going on?

Nailit69

I decided to do a compression test before I start chasing gremlins... I did 3 separate tests and #1,2,and 4 held steady but #3 got lower w/every check. On the first check they were all w/in 1-2 psi of each other, but #3 got lower by 10psi or so w/each test.

Engine cold, turned over until start and shut down

#1-150 psi
#2-150 psi
#3-150 psi on the first test, 140 on the second, 130 on the third
#4-150 psi

What could be the causing of the loss of compression on #3? Stuck valve? Cracked head? Or something worse?

I'm thinking about borrowing/renting a bore scope if I can find one and taking a peek in the #3 hole

Any suggestions before I tear into it would be most excellent!

Nailit69

Well it's not a stuck valve, they all move... i took the valve cover off to check out the valvetrain and everything looked fine in there. I did adjust the valves... which were closer to .008/.012 cold, now at .008/.012 at operating temp., a couple of them were a little tight after it warmed up. It still didn't solve my problem.



Everything is nice and clean though, looks good to me but i'm a Carpenter not a mechanic. I need to replace the Tstat anyway so i'm going to look at that injector... actually all of them. I might just send em all in for a cleaning and get new o-rings/seals. It still doesn't explain the different compression readings on that cylinder though.

I really don't want to pull the head but if I can't fix the miss w/an injector cleaning what else could it be? The erratic compression readings are leading me to think it's a bad valve, cracked piston/head, or a bad head gasket, isn't that about all that's left or am I overlooking something or did I buy a POS.

Nailit69

Well I went ahead and pulled the injectors and when I popped the fuel rail you could smell the bad gas... I drained it and put it back together and sure as schmidt it runs like a nascar champion. It's still a little sleepy still but it's alive and kickin

JohnnyCanuck

sweet, well done.

Dirt Driver

Running low-z injectors with an ECU designed for highs will burn up the injector drivers. An ECU with current-limiting drivers for low-z injectors will drive high-z injectors just fine. How well it works will depend on other factors.

That is a myth. Backpressure is nothing more than restriction and restriction doesn't do anything beneficial. Short, open exhaust kills torque for other reasons like changing the exhaust's resonant frequency.

Give that cylinder a squirt of oil after getting initial compression results. if the oil makes compression go up a lot, then the rings are suspect. If not, then it points to a gasket or valve.

If your truck is carbureted, then that's a given. If it's EFI, then it should have an O2 sensor.