I’ve been having a nagging problem that I can’t seem to resolve. I keep getting error codes P1171, P1174 – Additive injector adaptive fueling, lean limit exceeded RH & LH bank. This sometimes is accompanied with P0304, P0305 – Cylinder 4 & 5 misfire and P1300 random/multiple cylinder misfire detected. I get a set of errors about every 20 miles I drive. The truck seems to drive fine; I just get a subtle miss and then the codes pop on. Sometimes you don’t even feel the misfire.

Some history:
@ 91,500 I had the heads rebuilt, installed Bosch 4+ plugs, Magnecor 8mm wires and new coils (one was bad, replaced both) – had coolant leak and misfire on cylinder 7
@ 112,000 replaced all 4 oxygen sensors (from Atlantic British) – had O2 errors
@ 112,200 the O2 errors went away but I’m now getting the P1171 & P1174 errors. Replaced MAF (Bosch one from Atlantic British). No changes, still getting errors. I’ve had the intake system checked for vacuum leaks, as suggested in an earlier post, and did not find any. I’ve always used high octane fuel since I got the truck at 81,000.

I’m now leaning toward possible restricted fuel injectors as the root cause of the errors. In my search of past posts not much talk about fuel injector and cleaning them. Is there a preferred method of cleaning the injectors without taking them out? Has anyone had success using an additive to the gas such as Seafoam? Or, do I need to bite the bullet and pull the fuel rails and have them cleaned by a shop?

 

Seafoam will not clean fuel injectors period, there is so little naptha and alcohol in seafoam that when you dilute it it does nothing (you gas has more alcohol in it). You need to use a PEA based injector cleaner like techron. That is assuming you have clogged injectors and that they are clogged on both banks. Gas has so much ethanol in it these days that clogged injectors happen infrequently though it does happen. Since it is on both banks have you checked the fuel pressure? Maybe your fuel filter is clogged or your pump is going bad. You are probably on the right track though.

 

There is no fuel filter on a DII.
I doubt it is a clogged injector, but you can fill up with a good gas, like Shell and then add 2 bottles of Techron and run till the low fuel light comes on.

 

The filter is in the pump, you know that spike

 

That is not a actual filter though, it is a strainer, all it does is keep chunks out of the fuel pump.

 

Yes there is a course filter in the pump but there is also a fine filter.

 

I picked up a gauge to test the pressure of the fuel pump today. I got a pressure of 54 psi with the engine running at an idle. Looks like the fuel pump is good. I dumped a can of techron injector cleaner into the gas tank even though I doubt this will do any good.

Any other ideas on what may be causing my P1171 and P1174 errors before I give up.

 

You probably need like 3 bottles of techron if the injectors are that bad. Definitely could be the injectors it's just odd that both banks are giving you lean codes, usualy those come from bad O2 sensors or a bad MAF but you cleared those up. If you have the time pull the fuel rail and get it tested though if you know a good mechanic that knows diagnostics (few and far between these days) they may be able to find your problem.

 

Should I put all 3 cans in at the same time or should I spread it out over a couple tanks of fuel?

I really don't know of any place to take the injectors if I take them off. Anyone know of a place to take them in the Los Angeles area?

 

Well depends on how risk adverse your are. 1 can of the "new" techron treats 15 gallons (unless you bought the bigger one that treats 20). Our tanks are 25 gallons. I've put 3 cans in at once and saw no harm (saw no benefit either) but my engine is fairly clean inside. People with stuck fuel senders will put 3 cans of techron in 4 gallons of gas so it will more than likely not hurt anything. Will it help? Depends what your problem is.

Can't help with a shop.