<style> <!-- /* Font Definitions */ @font-face {font-family:Cambria; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:0; mso-generic-font-family:auto; mso-font-pitch:variable; mso-font-signature:3 0 0 0 1 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0in; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-ascii-font-family:Cambria; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:Cambria; mso-fareast-theme-font:minor-latin; mso-hansi-font-family:Cambria; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} @page Section1 {size:8.5in 11.0in; margin:1.0in 1.25in 1.0in 1.25in; mso-header-margin:.5in; mso-footer-margin:.5in; mso-paper-source:0;} div.Section1 {page:Section1;} --> </style> Ok so here’s the deal. I just got my hands on a 1990 F350 with the 7.3l N/A attached to a 5sp manual in it and has 4wd. Bone stock aside from having a utility bed. When it got nice and warm after driving for a while it started to have a really rough idle. It seems like it is intermittent as when I idle the truck long enough it calms down. It’s still abnormal but not nearly as noticeable. The cab rocks a bit and the shifter rattles in my hand excessively. Also you can hear “fwouph fwouph fwouph” sound from the tail pipe as if the truck is puffing out air. The facts:

- Odometer reads 148K
- Tachometer reads 400rpm at idle and warm (Truck in neutral and E-brake on with T-stat gauge with pointer on the left edge of the “N” of normal)
- The IP looks like the original (Still have red epoxy on the screws. Really clean compared to the rest of the engine though)
- No clue if the injectors are original or not. All associated hoses look good and have no visible signs of leakage
- No odd smells out the pipe or under the hood
- Replaced Fuel filter and ran some D-Kleen
- Replaced air filter (Plan to cut off soup bowl next)
- Restricted filter sensor is bad and has a leak
- Fuel heater connector doesn’t stay on
- Seems to drive fine. (Does feel like it looses a little bit of power on hills. I can’t really say for sure because this is the only Diesel f350 I’ve ever driven and when I downshift from 5^th to 4^th it scales them like mtn goat)
- Absolutely no smoke except right at a cold start up where there’s a small puff of white followed by a bigger puff of black. I don’t even recall seeing much smoke in the rear-view when I hammered on it.
- Starts within 3 sec any time every time. (I live in the bay area of CA so the weather is mild right now. 40’s at night 60’s during the day)
- Once warm it cranks over with a flick of the key
- Checked coolant for diesel fuel and is clean and good.
- Was low on coolant when I bought it added a bunch to the system and no change in performance.
- Have not changed oil yet, but it is jet black. Not sure if it is some kind of special oil or what because it doesn’t look like conventional oil when it gets dark from being run too long. Viscosity is good and there doesn’t seem to be contaminents.
- Truck came from a seriously dusty environment. (Lot’s of dust in engine bay and in cab was used on construction sites a lot.)

And that’s about all I can think of. The thing is a beast and great on the highway as with the overdrive 5^th gear I can cruise at 70 and keep the rpms in 2400 range as I hopefully read correctly is the best place to keep the rpm to get good mileage. My next diagnostic plan was to go through and crack the injector lines open and see what it does to performance to maybe isolate a bad injector? I imagine at this mileage it would be best to buy a whole new set of injectors. What should I pay for that? I plan on doing everything myself.

I’m sorry if this is a lengthy and repetitive Noob post, but I have read through tons of information online and have not found anything that points to one specific problem. Plus I need as much information as possible before I spend any more money or time on my hair thin budget or do anything that my disable my truck for too long. This is my workhorse and my business needs to rely on it heavily in the coming weeks. Thank for all the help in advance.

 

Bump the idle to 6 or 7 hundred rpm first, 400 seems way too low. Does it run ok off idle? Like at or just under 1000 rpm?

 

Ok, so I got the idle up and the sensor removed and plugged. To answer the running question, it did run alright. The throttle response definitely got more pronounced at or around 1k though. After the idle rpm tuning the overall idle improved but is still off an on pretty rough and I am hearing some odd groaning sounds in the cabin now. The acceleration after resetting the idle definitely got a whole lot better and the idle tailpipe odor is much more like cleanly burning diesel. After running it up and down the block a few times the idle is at the curb is 750rpm. and there is no roughness. The strange exhaust sound has been reduced to what sounds like a small exhaust leak. I've been under it a few times already for other things but havn't seen any soot marks to suggest a leak. Going to see what happens after letting it sit overnight and see if the rough idle returns. Got my fingers crossed though....Thanks for the fast and helpful response!

 

that 750 rpm is just about right. i can't even imagine what my truck would sound like at 400 rpm. at around 700-650 it sounds weirdLOL. i have mine around 800rpm for my E4OD.