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83 F150 straight 6 has fire and full but won't start

My friend borrowed my f150 and after a very loud backfire it will not start. It gets a spark, has between 90 and 100 lbs of compression in all cylinders and when cranking around the dampener it appears the rotor is at cylinder 1 at TDC. I have also dumped a little gas in the carb to no avail. The interwebs seem to point to a timing gear skip. What should I look at for this? without removing the timing gear cover?



  • It gets a spark How do you know?
  • How did the plugs look and how did you confirm the spark? The timing gear may have "jumped" but the usual failure of the timing gear is the cam gear strips out and no longer turns. The factory timing gear is some composite that falls apart like saw dust. It usually fails when the engine tries to run in reverse when attempting to start. And the compression should be well in excess of 120 psi.
  • Those inline 6-cyls are near bulit proof.. HOWEVER they are known to blow there head gaskets right around 200-250,000 miles..LOL, I know it seems high mileage to have a known issue, but many of them hit this mark.. So many infact that the head gasket issue is known. This would explain your low compression as well.

    Less likley, You could also have damaged the carb so bad it is flooding the motor and that is why you will not start.. Try this.. Remove the fuel line from the carb and put it into a fuel jug, spray starting fluid into the carb.. Will the truck fire now??
  • I know it is getting a spark cause I put a screwdriver in the end of the plug wire and held it over the valve cover and it sparked,

    The plugs looked like they should according to the photos in the chiltons. The timing gear is turning because if I crank the dampener around I can see the distributor rotor turning. The compression was this low the last time I tested it which was the last breakdown it had 2 years ago.

    I have tried starting directly on gas and carb cleaner to no avail.

    At TDC should the rotor be directly under the #1 plug on the distributor cap? Also the rotor has some rotational play in it. Is that normal?

    thanks for the help

  • At TDC the rotor should be at #1 or 180* from #1. Have you checked the compression with oil in the cylinders? If not check it and also check for manifold vacuum while you check compression. And, prior to this problem, how was the engine running? Possibly losing power!
  • How does one check the manifold vacuum, I assume with a vacuum gauge? I have not done an oiled compression test.

    The truck has always run somewhat poorly but good enough for the occasional wood/garbage/manure/mulch runs I take it on every couple of weeks.

  • A vacuum gauge is less than $20 at most McParts stores or Harbor Freight. But before buying the gauge remove the carburetor and then disconnect and lift the EGR valve and spacer off the intake. It may be broken and causing a massive vacuum leak. If the EGR is broken, remove it from the spacer, cut a soda can to fit at the EGR port and block it. Then try to start.
  • my EGR is already blocked with beer can. when I got the truck the beer can had burned through and I replaced it with some more but maybe it is burned through again, In the past though it had to be warmed up before the EGR opened and killed the engine.

  • A BEER can....... There are some true mechanics involved here. That truck might last forever. The EGR spacer can break apart. If that's the case the beer can would be needed under the spacer plate at the exhaust inlet. Wait till tomorrow to test drive or stay in the yard. BTW, I just popped a Lone Star. Good luck.
  • Unless your computer sets your timing, and I'm pretty sure it did NOT in 83, you should have some rotational play in the rotor. That's your mechanical advance.
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