Its been over 6months now, I have not been able to fix this truck or drive it...

Truck
1998 4.6L F-250 LD 118k miles

Maintenance history: UNKOWN (bought "As-IS" told it needed "tune-up")


Symptoms:
Truck shakes BAD at idle, sometimes hard to get running when cold out.

-Throttle seems very responsive, revs quickly and smoothly

-Seems to be skipping/misfiring at idle...

-No check engine lights ( 6months ago I had a few random misire codes I cleared) been sitting in my driveway FOREVER.

-sometimes "popping" from intake

Replaced/checked parts:
Spark plugs
Wires
Fuel filter
coil packs
Hose from intake manifold to PVC

I've checked various vac. sources and even attached a vac gauge to the truck.. I think it was around 17VAC.

I cannot afford to take this into the shop and really need it to start running... I am running out of options... Does anyone have any suggestions?


Do these motors need a complete rebuild at 100k miles or something?
Dead cylinders?

What commonly causes this poo-poor idle that SHAKES the whole truck real bad, barely runs when first started but smoothes out as soon as you give it gas....

Truck feels kinda underpowered (I have a 6.0 Turbo diesel, poor comparison but its feels SLOW)

Any help would be greatly appreciated... this is really killing me

-Brad

 

Any codes now? I would suggest checking the vacuum hose at the rear of the intake manifold from the PVC valve. These tend to rot out over time and produces a pretty good leak. The vacuum guage reading seems a little low.

Speaking of a dead cylinder, have you run a compression test? Typically, the Triton engines won't need a rebuild until upwards of 200k - 300k miles if properly maintained.

What plugs and wires did you use? Good luck!

 

No codes at all

I JUST (half an hour ago) installed a new PVC hose on it, thinking it was it... did not fix it at all - the hose didnt seem to be in bad condition at all-

No compression test yet, do they tend to have cylinders go bad? Why?

 

My truck stumbled very bad and shuddered taking off, skipped etc., I had a vacuum leak at the back of the engine and a custom molded elbow near #3&4 cyls under the hoses that was not leaking but collapsing in on itself. Once I got all of the vacuum issues straightened out it cleared right up and has been running better the more I drive it (I also put a bottle of fuel inj. cleaner in last tank but I am sure it was the vacuum issue. That was my most recent shaking shuddering issue, in the past it has always been bad coil packs, the vacuum issue was a surprise.

 

I had an intake noise popping sound...shudder in over drive between 45 and 60, and it would shudder from a dead stop...
Ended up being moisture in cylinder #1 COP and plug area ...I had a code # p0301...and the check engine light flashing...I blew it out with compressed air and no problems any more...

 

sound like an IAC problem to anyone else?

not that familiar with this engine, not even sure how i stumbled onto this thread, but thats the first thing i thought of.

 

I was thinking IAC too. Not exactly "classic" symptoms, but I'd say worth a try.

 

When driving it if you TURN OFF OD it seems to be better....

I'll check the IAC... I tried once to remove it, afraid I was going to bust the bolts...

Thanks for your replies.

 

IAC needs cleaned or replaced. The poor idle is the hint while it revs fine and smoothly.

 

ok,here is one for you...

got a 97 with a 4.6 lots of miles.. odemeter stopped working a few years ago and shows 129,000. drove the thing every day, its a work truck.

Crossed a set of very rough RR tracks and the truck stalled. Would not start back up, found a bad PCM main fuse was blown. Changed it, truck started and ran like yours, rough, weak. dragged it home and checked it better. found a piece of wire attached to the starter, dunno why, removed it, thinking that caused the arc problem. pulled codes, rear o2 sensors bad. Changed both o2 sensors and plugs (needed them too) and still runs weak and poor. not enough power to pull up a set of ramps or slight incline.

only code flashing is EGR. This runs so poor, we are now thinking that maybe its out of time. Has anybody else had this problem ?

 

You may have a cam follower that has dislodged or a broken valvespring on the cylinder that is misfiring.

 

Jeffdoer, I just finished going through a thread that reaches to the end of the internet on EGR problems. Apparently the 4.6 is notorious for clogged EGR ports when the milage gets up there and there is a possibility of a bad DPFE, emission arent my thing but I think that thread will help with EGR issues.

https://www.ford-trucks.com/forums/2...-egr-flow.html

 

Wouldnt that make all sorts of noise?



UPDATE: I applied vacuum to my egr and the vehicle did not stall, nothing changed at all

So I am thinking...

1. The egr tube is clogged and the vehicle runs like poo due to something OTHER than the EGR BUT the tube is still clogged

2. The egr is stuck OPEN and replacing it will make my idle alot better...


I guess it could go either way, I will test my theory when i get more time...

 

The egr is stuck OPEN and replacing it will make my idle alot better...

I'd try this stuck open would do as you say
bruce

 

The egr was NOT stuck open, applying vaccuum to it still operates it. The TUBE was destroyed at the bottom where it mounts to the manifold... would an exhaust leak here cause this issue?

-Brad