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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.

After a more thorough check the rotor is about 25 degrees before the #1 plug post in the distributor. My mechanic friend says it should still run like this. What do yall think?


Rotate the damper first forward then backward while you watch the distributor rotor. How far backwards can you rotate the crank before the rotor starts to move backwards.?? If you can rotate it 20 or 30 degrees before the rotor reverses, then there is way to much slop in the timing chain and it probably has jumped time…Another test, reach into the oil pan drain hole with a coat hanger and see if you can drag out any little pieces of plastic. If you can, they are the former covering of the cam gear, which are plastic coated so they run nice and quiet. But once the plastic starts breaking off the engine can easily jump time as the chain slips over the very worn gear teeth…

It is a very very very common thing for the FIBER teeth on the cam drive gear to "chunk out and lose teeth yet still spin things but not at the right times. So, replace them and you’ll probably have this licked. The teeth aree fiber so you don’t have a gear “whine.” There is no chain at all.

KAWASAGA STOLE THE WORDS RIGHT OUTTA MY MOUTH…YOU NOW HAVE A CAM TIMING ISSUE…DO A TDC test and observe where the rotor points within the distributor…I bet it doesnt line up with the #1 cyl any longer…THAT BACKFIRE announced the Timing failure…of whatever nature.

I have owned 5 F-150’s with the AWESOME inline 6…They are known for this issue unfortunately…that is their only known fault actually…that I know about anyway.

YOU MUST check the distributor rotor allignment when at TDC …You jumped time for whatever reason…this is your issue

Caddyman and Kawasaga nailed this one…

Honda Blackbird

After a more thorough check the rotor is about 25 degrees before the #1 plug post in the distributor with the damper at TDC.

Thanks For all the advice. I’ll start pulling the timing gear cover this weekend. Are the replacement timing gears also plastic coated? I really don’t care if they run loud.


I will just add that the compression readings you cite flat suck. It sounds like the entire engine is worn out so I would be a bit antsy about getting too deep into this thing.

You might revisit the compression issue by performing a wet compression test on it. Odds are that you will find the rings are gone.

Let me add one caveat to that. That would be assuming the timing chain has not jumped some teeth. If the chain has not jumped then that motor has problems and at this point I’m still inclined to think it’s just flat worn out.

There has never been a timing chain in the 300 6 cyl. EVER!!..Always gears!!! and often fiber cam gear teeth for noise. The teeth always come off in small groups and allow the cam to still turn but greatly retarded resulting in no-start, poor compression. So, cut to the chase and pull that front cover off. Do NOT hammer on the cam to put the gear on or you will be guaranteed to knock the rear cam plug out and have a major oil leak in the bell housing.

Removing the harmonic balancer will be the toughest part…

When you buy the replacement parts, you will probably have a choice of a fiber cam gear or a metal one. Ask if they have a “Timing Gear Kit” which will contain all the parts you will need, including a new front main seal…