This weekend i put in a NAPA reman 351 with comp cams basic replacement cam in my 92 f-150. On sunday I got it in and drove it around 40 miles and evey thing seemed good, maybe alittle doggy but over all ran good. Then I went back home over the mountians about 250 miles and on the hwy and it did not have any power at all. It ran worse than my old I-6 did and on top of it it only got about 9 mpg allot worse than the 16 mpg i got with the old 200k mile engine. I thought it might be timing and was planning on checking it the next day after work. This morning when going to work it was very cold out and it started fine and ran the same. At noon it started and then died and would not start again. it sounded like it was out of time really bad, would try to start but would not grab hold. Later to day i went back to try and get it going. IT started but I had to keep it going for a min or two then it ran like it has been. I checked the timing and it was at 10 BTC with spout diconnected. When gased it advanced to some where around 30 degrees. One thing that seemed strange is when you let off the throtle it took quite a while for it to return to 10 degrees. other than that i dont know any thing else. All I can say it it has no power, firing order is correct and timming is set at 10 degrees. Any other ideas. This has been a pain, after busting my *** this weekend to get the truck done and all the money and it dose not run good
Really appricate any feed back
Thanks

 

Plugged exhaust?

 

I have never thought of that. It did have a really bad exhaust leak when I put it in and i really had to fight it to get it to quit and also this morning when it was cold, it was blowign tons of condinsation out the exhaust, more than i have ever seen. How can i go about looking into this further to see if maybe there is something in the cat or mufler that is causing an obstruction?
Thanks for the idea, any thing else?

 

Perform an intake manifold vacuum check to determine if there is an exhaust restriction

 

Sorry for all the questions but how is that done?
Thanks

 

Attach a vac. gauge to any manifold vac port. break open the thorttle, the vac should go down and then go right back up. Restricted exhaust will give you the lower vac reading when the throttle is open and then will stay low or come back very slowly.Is this motor a replacement for the 6 cyl ?

 

Thanks i will try that, and the truck has always had the 251, the i-6 was in my last truck.
Thanks

 

Don't forget that the timing is checked with the spout connector unplugged and at @ 1200 rpm ( not idle) If you still have the emmission sticker under the hood it should have the exact reference rpm for the timing.

 

can you tell me how to set the timming. I set it at 10 btc with the spout disconnected, but there was no sticker and i had no idea i needed to set it at 1200, Do you just have to have someone rev it up to 1200 while the timing is set?
Thanks for the input

 

Don't hold me to the 1200 rpm. I know it is about that. The EECIV ignition systems with spout connectors still had centrifigal advance in the dist. You needed to time them above a certain speed in order to get the cent. open ( never understood it, Ford did this for several years starting in the EEC III days. ) I used to use a small wedge behind the throttle stop to get the rpm up in order to time it correctly. If I remember correctly if you did time it at idle you would normally be running retarded by several degrees. Helps if you have a light with an advance dial on it. Set the dial for the advance you need, run up the rpm and put the mark at TDC. Been quite a while since I have had to do one but I have done my share and its not something I have totally forgotten.

 

Thansk i will give that a try also

 

Your reading will vary depending upon your altitude. I can't give you "good" numbers but I can give you a fairly good method for checking. Attach the vacuum guage to an available direct manifold port. Start the vehicle and check vacuum reading at idle. Snap throttle open and observe guage, it should drop by at least 4 (inches of mercury). Run the engine up to 2500 R.P.M.'s, hold steady and observe reading. Your reading should be approximately 2 (inches of mercury) higher than it was at idle. If these conditions exist your exhaust is likely not the problem. If your results do not meet this criteria further testing may be necessary. These tests don't isolate the exhaust exclusively. Other problems can cause similar readings but it's a good place to start looking particulary used along with an accurate compression check.

 

This is not correct.

 

Thansk for the info on the testing the exhasut, in regard to Danny's comment, just set the timing at 10 btc at idol wiht spout disconnected?
Thanks

 

I just put a vacum gage on the engine and and it seemed good 17in hg at idol. When i hit the gas it droped to about 5 and when i reved it up it did read higher than at idol around 24 hg.

One problem is at idol the dial jumped around. THe book said is it moved slowley it was the mixture and if it jumped around very fast it was valves etc. I would ay it it was jumping around pretty slow. It also idols a little rough and it had the same problem with the old engine. Have replaced o2 sensor , and EGR sensor and valve. Could the MAP sensor be the problem. IT dose not have any fault codes. If it is the MAP where is it and how can i check it.
Thanks