Engine issues

homelessduck

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Hey guys :)

I have a '91 suburban with 6.2. I'm having issues with it. From idling to a few hundred rpm's higher it runs super rough, no power, shakes to the point of breaking motor mounts. However, it then clears up and sounds CRISP. It fires right up, no excess smoke once it's warmed up. It does smoke a good amount ( grey) when first started but I have been pulling injectors and messing with fuel lines so it has had a lot of air in the lines, and I don't start it very often. I warmed it up while watching each cylinder with a temp gun and noticed some cold cylinders. I pulled the injectors and tested them. They had horrible spray patterns, weren't atomizing, dribbling .. I took them apart, cleaned and reassembled. They tested much better so I tossed them back in. No change. I cracked each line and every one made a noticeable difference. Fuel pressure at the filter is 8psi.


Any suggestions? ? It isn't super bad at idle but just off idle it starts shaking, a few hundred rpm's more and it's clear.
 

towcat

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low rpm miss to high rpm smooth injectors are highly suspect.
low rpm miss and gets worse at high rpm pump is suspect.
 

homelessduck

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I guess I get to pull them all and see what's going on .. So they shouldn't dribble AT ALL correct? They're suppose to hold pressure then pop? I bought a reman injector to compare mine to and it dribbled worse than mine, haha.

Does anyone know what the p/n is for the needles? Or where to get them? I read somewhere they could be sourced through rockauto but I have no idea what I need to rebuild these or how to figure out the p/n's.
 

79jasper

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Tanman seems pretty knowledgeable on these.

Definitely shouldn't dribble at all.

Are you using a pop tester?


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tanman_2006

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No dribble and should spray a good even mist. No side squirting.

Mel rebuilds 6.2/6.5L injectors. If non turbo ~2000 psi would be good for clean burn and economy. Stock can be 1600-1800 depending on rebuilds and what specs they went for (1500,2500,3500, or military), everyone did their settings a little different.

Scribe a mark and try adjusting timing and see if it helps before ripping it apart, its possible to shear the pump drive key but still run the pump with timing way off. The built in timing ramp of the pump could cover it with RPM change. You will be retiming after injectors anyways so what would it hurt?
 

homelessduck

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Yes, I'm testing them with a pop tester.

I'll give it a shot, thanks.
 

homelessduck

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I decided to play with the timing before pulling all of the injectors. The timing was aligned exactly to the two marks so it was easy to remember where it was without marking anything. I moved in very small increments both ways, it just made it run worse. I put it back to where it was and it still runs worse than before. Now it is knocking and smoking really bad. .. The smoke is grey.

Maybe an injector decided to stick?
 

tanman_2006

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To check for a bad injector, either go through and loosen each injector or pull each glow plug one at a time. If that's the problem the knock will go away when you release compression or remove fuel from that cylinder.

Could be a bad rocker button and I still wouldn't rule out the pump drive being twisted.

Source Unknown
 

homelessduck

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I pulled all of the injectors. I found one stuck open. The best one popped at 1500. The rest were around 1300. They all dribble slightly under pop pressure. What pressure is ideal with a turbo? How do you guys make shims ..? Could I just use a washer the same size or is it not that easy?
I know I could source them from other used injectors but money is tight and I don't have access to any.
 

lindstromjd

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Makes me want to go check my storage unit for the set of rebuilt injectors I got and send them to you, just to see if it makes your problem go away. I have no use for the set since I bought a set of marine injectors to use in my engine.
 

homelessduck

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Makes me want to go check my storage unit for the set of rebuilt injectors I got and send them to you, just to see if it makes your problem go away. I have no use for the set since I bought a set of marine injectors to use in my engine.

I sure would appreciate that! I'll pay shipping both ways and I would send them back nice and clean :)
 

Agnem

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If those don't help you out, give me a call. 717-806-5561 and see what we can do for you. It sounds like your fuel system is getting pretty worn out, and you really could use a pump and injectors.
 

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