Lost on 99' 3.0L

[offroader83]

The starts right and for the most idles fine. When you try to give it gas it will start to spit and sputter. Gettig 55 lbs fuel pressure. Has new MAF, tps, all new gaskets from the head gasket up, new plugs and wires, cps and syncro. The other day I had unplugged the flex fuel sensor and it ran like a top but then the next day it ran like crap again. Not kicking any codes. Checked for vaccum leaks with can of brake clean all over top half of engine. The iac looks to be fairly new. I have only had the truck for about a month now and still have not been able to figure it out. Had a shop take a look and they did a quick look over and told me it had an internal vaccum leak. The reason why did all new gaskets but not just lost with it. Hate to get rid of it but need vehicle for work pretty bad tho. O did have codes for running lean bank 1 & 2 but when put new maf sensor on that havent came back yet. Thank you to everyone that can help.

 

[RonD]

Unplug IAC, if RPM drops and/or engine stalls you do not have a vacuum leak.
If idle doesn't drop you do have a vacuum leak.

 

[stmitch]

I'm leaning towards a clogged fuel filter or bad injector(s). The fact that it is fine when at idle but stumbles under load, when the engine would need more fuel suggests that it may be fuel related.

Seems to me that a vacuum leak would be more evident at idle or startup when the engine is cold, and might get less severe as the engine warmed up. That sounds like the opposite of your situation to me, so it seems like the less likely option.

 

[JP02XLT]

With it running, pull the injector connectors 1 at a time, you should get a big difference from each one on how it is running, if not then that unit is the suspect injector.

JP02XLT

 

[Rearanger]

When you try to give it gas it will start to spit and sputter.

Under all conditions? From stop and idle and/or at speed when accelerating?

 

[offroader83]

Will try the iac again and see what happens. Can only get to some of the injectors tho because of intake. Will post back with some results. These results are from it sitting in park and when in drive trying to take off. Cant get truck up to any speed.

 

[Rearanger]

The IAC has no effect once you step on the accelerator. Look somewhere else.

 

[offroader83]

When started the truck at first didnt want to stay running. Finally got to stay running for little bit motor would drop rpm then come back up. Unplugged the iac and the rpm dropped really low to was barelly running. Going to try and recheck vaccum line under the phenom

 

[RonD]

If engine idle dropped to barely running with IAC unplugged then you have no vacuum leak, look at fuel pressure as the cause of the problem, i.e. fuel filter or fuel pump.

Also with engine idling check tail pipe you should have good flow coming out, if you don't feel much coming out then exhaust system could be blocked, collapsed cat converter or muffler issue, this blockage won't allow engine to rev up, and it would be hard to start.
Or some one shoved a potato up your tail pipe...............that trick just NEVER gets old, lol.

 

[offroader83]

Last i had the fuel pressure checked they said 55 psi. That the book I have says that is still in good range but not sure. Gonna go ahead and replace filter and see what comes from that.

 

[offroader83]

Checked all the injectors with probe and they all 6 are clicking so not an issue there I think.

 

[offroader83]

Well changed fuel filter and no change. Did some checking tho and everywhere I looked said fuel pressure should be between 55-75. Thinking about blocking off all vaccum lines and see how it acts. When its after sitting its real bad at idle and gets slightly better as it runs some but never stops dropping when idling and cant give it any gas at all with studder and not accelerate up

 

[JP02XLT]

Is it rich or is it lean when it does this? You could easily remove the intake air tube and give it a small shot of carb cleaner while its trying to rev up, if it helps you have to be lean / lack of fuel delivery.

As for the injectors, you checked that they are cycling electrically, there still is the mechanical function of passing fuel, plugging / unplugging them while running will give you an rough indication that fuel is passing & your completely cycling the pintle in the injector, sometimes that will dislodge a blockage on the tip. Trust me I know they are difficult to get to on your 3.0, you should see them with the SC/intake on that motor, they are very buried. Otherwise your other option is to remove & have them cleaned and checked.


As for the fuel pump you checked and had 55 psi, that is only part of the test procedure, you need to remove the fuel line and perform a volume test.

Also have you checked the vacuum line on the fuel regulator to see if it has any fuel in it and possibly leaking?

Do you have the old MAF, maybe retry it and see if anything changes, maybe you have a bad new MAF

Also what do the plugs look like? Pull one of the easy ones to check color.

Dont mean to throw a bunch of stuff at you but there are several things that could be causing your symptoms, some easier to find than others

JP02XLT

 

[offroader83]

Gave intake a direct shot of starting fluid while trying to rev up and it reved up great. Pull connectors off 4 injectors and noticed idling defference. Have to pull top half of intake off to get to the other two.

 

[Rearanger]

Hard to believe multiple injectors are your problem.

The TPS is responsible for telling ECU when to give extra shot of fuel when throttle opened - much like old accelerator valve on carburetors.

It may pay to check that TPS to make sure it's sending signal.