I'm not sure which forum to post this in, but this is my best guess. I've got a '78 F150 with a 351M. It sat for 20 years in a garage until two years ago when I started getting it ready to drive. I replaced the gas tank, all rubber fuel lines, sending unit, fuel pump, carburetor (rebuilt), and cleaned out all hard lines. The truck ran fine until last week when it just died while driving down the road. I towed it home, and replaced the fuel pump again. That didn't work, so I blew out the hard line from tank to pump, and it was plugged. Once I did this, it was fine. The last few days though, I've been having a problem at idle. It seems to run really rough. Like I've got the idle set way too low. Last night I dropped the tank and the sending unit screen was packed with small black "gravel". The wierd thing is that this was on the inside of the screen. I cleaned it out completely, and cleaned the lines out again. Then put everything back, and all seemed fine until this morning. All day long I've had problems with it not wanting to idle. It runs great at higher rpm, but at idle it's like it's starving. I replace the fuel filter again today, and that helped some, but it's still acting up. Could the pump have some of that black crap in it? Would that be affecting my idle only? Sorry for the long description, but the more information I can give the better. Thanks.

 

I'd put a fuel psi gage on and see where your at.

 

good idea, I feel stupid for not thinking of that. But I guess that's why this site is so good. Thanks. I'll try that and hopefully I'll get this solved quickly.

 

Ok, been a couple of days of trying things and testing theories, and here's what I've got. I have replaced the fuel line from the pump to the carb while installing an inline fuel pressure gauge. I'm constantly getting a 6 - 7 psi flow from the pump into the filter. When the idle acts up it starts fluctuating from 2 - 10 psi very quickly back and forth. It almost sounds like it is missing. I am getting fuel now, no problem, but I still have the idle problem. It doesn't happen all of the time, but it typically happens once the motor is warm. I'm wondering if I have an egr issue. I also replaced the positive battery cable, because I had some serious corrosion, and I wanted to make sure that I was getting good connections everywhere. I know this post is all over the place, but I'm just trying to think about everything that I've tried the last few days.
Last night I pulled each plug wire off of the distributor one at a time to see if I could hear a difference, and quite honestly the engine already sounded bad enough that I could only hear a difference with two of the cylinders. I also pulled the plugs, and four of them were white. No ash or deposits at all, just white. And plugs in cylinders 6,7, & 8 were all loose. I have tightened them all down and still have a stutter at idle. Like I said, it doesn't always happen, but it's getting more frequent. Also, for the last few months. Say I'm going 20 mph, and I give it medium throttle, it sounds like a diesel until the rpm's get up there. I know this is a lot at once, and probably very confusing, but any help would be greatly appreciated. I am in way over my head on this old beast. I'd just like to have a good running engine.

 

My guess is a fuel pick up problem. I'm not sure what there is for a filter on the pickup, but if there is one, see if it is varnished up from all that sitting.

Remove the line that supplies the fuel pump and make sure that it is COMPLETELY clear. If the line is restricted, it will draw gas initially, but then not be able to draw enough to keep it going down the road.

 

The pickup sock is completely clean. When I bought the truck, I replaced the fuel tank, sending unit (including pickup) and all rubber lines. I then blew out all hard lines, and have since replaced the hard line from the pump to the carb. That only leaves the main hard line along the frame from the tank to the pump as the original. This past week, I dropped the tank and re cleaned out the sock on the sending unit and blew out the lines again. That doesn't mean that the hard line along the frame isn't still a little plugged, but I'm not sure what else to do. And if that line is what's giving me problems, why would it wait two years of running before it started acting up? Thanks again for the responses.

 

I went back and read the original post carefully. I have a bad habit of quickly perusing posts rather than concentrating properly on them.

If the engine will run at sustained RPM for a reasonable distance, then I can't imagine the fuel delivery from the carb back being your problem. It could, however, be that the crud is moving around in the fuel line. I wouldn't even dream of this being the case except for the fact that you saw the "gravel" in the tank filter after already clearing it out.

Have you tried spraying carb cleaner in the hard line and then blowing it out. Spray and blow out several times from either direction with something over the end to see if anything is coming out.

Sorry I can't offer any more help than this.

 

Don't be sorry, any help or advice is appreciated. It sounds stupid, but I haven't tried it with the carb cleaner. I've just used high pressure to blow it out. What do you think could be causing the problem with it sounding like a diesel? It only happens at mid to strong throttle, but not at full throttle. I'm not entirely familiar with egr systems, but from what I do know, this sounds like an egr issue. My ultimate goal is to go with a weiand intake, edlebrock 600 cfm carb, msd dizzy, coil, and ignition. I'd have the distributor curved for my application without the egr, but for the time being, is there any way to curve the stock distributor to be used without the egr? I have no emissions checks here, and my truck is a non-catalyst to begin with. The only emissions it has is the egr. I know the potential of these motors, I just want to tap into it a little. Any advice from those more experienced out there would be great. Thanks to all who read these forums, and especially those who take the time to respond with help or opinions.

 

The "diesel" sound could be detonation, does it sound like shaking a tin can with marbles in it?. This can be caused by not enough fuel, too much ignition timing, poor fuel quality, or a combination of both. Since your distributor is curved for no egr and you are running egr, I would possibly start there. Egr adds a percentage of exhaust gas in the combustion, but, this shouldn't happen at Idle, only a part throttle, light load. (On these motors I'm not even sure what the egr strategy is, most of my egr experience is on newer cars.) If you suspect the egr to be faulty, you might look into disabling it (that I can't help you with, but I know there are multiple posts on the topic here) or using an egr distributor. Have you cleaned the carburetor since you found deposits in the tank? The filters may not have caught it all, I'd look into cleaning it out really good. What is your ignition timing set to?

 

kettle, I haven't cleaned the carb since all of this began. You're right, the filter probably didn't catch everything, and that does seem like a logical next step. I do think my previous post was misunderstood, however. My distributor is not already curved for use without an egr. It is bone stock. I was wondering how to curve it to be used without an egr. I know that there is a big debate on whether or not to remove emissions for better power, but this isn't exactly my goal. I'm just trying to make this engine as simple as possible. That helps a lot in the troubleshooting department. And there isn't anybody out there that will convince me that emissions equipment doesn't complicate a fairly simple process. By the way, my initial timing is 14 degrees as per the sticker on my valve cover. I know that my mechanical and vacuum advances are also working properly. I've checked these, and everything is good. This is why I'm guessing my egr may be acting up, because it seems like a timing problem, yet my timing is dead on. I know that the egr's functionality is heavily dependent upon proper timing, and vice versa. Thanks again for the help. Looks like my next step is to clean the carb. If anybody can tell me if the stock distributor can even be recurved for non egr use, and how that's done, that be great. Thanks.

 

dilbone56,

You are probably a lot younger than me. With modern cars, you very rarely, if ever, hear detonation because modern FI uses knock sensors to sense it and then retard ignition to prevent it.

With the older cars, preignition occurred under many circumstances. WHEN it occurs, it indicates too much timing and in some cases a coinciding lean condition. Since you hear it at different times under varying loads and throttle positions, you are probably dealing with a distributor timing curve issue. This does not mean the distributor is broken, just does not have the correct centrifugal and vacuum advance characteristics.

 

On you initial timing, I thought the factory setting was around 8-10 deg? You might try pulling some back after you clean your carb and if the issue persists. EGR in not a bad thing and only works under certain situations. That said, failing EGR components could cause issues.

I found this to be a good read.

https://www.ford-trucks.com/forums/8...-a-diesel.html

 

That thread was a very good read. I will clean my carb out and then work on the egr and distributor issue. That kit from crane is exactly what I've been wanting. Thanks.

 

Let us know how it goes. I need to buy that kit too, but I have no EGR system and an EGR set distributor.