88 Dakota 3.9 issue

My 88 Dakota 3.9 quit yesterday, and I had to drag it home. It had
begun running rough and would only go if I kept the throttle mostly
open, then it quit. Based on what I saw when I was troubleshooting,
I've begun to wonder if it could have skipped a tooth on the timing
chain. The motor has 140K on it, but hasn't been a problem up to
now...

I checked the cap and rotor, and there was a fair amount of wear on
the contacts, so I replaced them. I checked for spark and have that.
It smells gassy when I crank it, and it cranked faster than normal.
Knowing that it had spark, and apparently gas, I shot it with some
ether while cranking and it didn't catch at all. I know that the
distributor is turning because it had changed position when I popped
the cap off. To top it all off, the starter wasn't engaging
reliably. Are there any timing marks that are external to the
engine? Are there any other common problems that can cause this sort
of thing?

 

your symptoms sound a lot like jumped time. there have to be external
timing marks but I don't know where they are.

nate

 

to check for a jumped timing chain locate #1 cylinder on the
distributor, mark it with a felt pen, remove the cap and turn the
engine over until the timing pointer lines up with the TDC mark on the
crank pulley. The rotor should point to the #1 mark you made or 180
degrees from it. If this is not the case you likely have a jumped
chain.

ch

 

If the compression is good then there is nothing wrong with the timing
chain. If the compression is low in all cylinders then the timing
chain has jumped.

 

cranking faster than normal sounds like a jumped timing chain, but the
compression test will tell you for sure.

 

Is it possible that the engine is flooded so that is washed the cylinder
walls down causing a loss of compression making the engine crank faster? If
not Check you crank to distributor timing. If it doesn't line up. It is
possible that the distributor gear bushing siezed caused gear to force
upward and skip a tooth on the cam shaft. It will be easier to remove the
distributor and check the drive gear position in the engine block when at
tdc then to remove the front cover.
Good luck
Bryan

 

It does sound like a timing jump. An 88 3.9 is probably like a pre-92
318 in having a plastic-coated "silent" cam gear, which sheds its
plastic coating and lets the chain go slack enough t0 jump time
eventually. If you haven't touched the distributor other than changing
the cap and rotor, check your timing with a timing light while having a
helper crank the engine. If the timing chain slipped, the distributor
timing will also be way off and that's a dead giveaway. You can, of
course, set the ignition timing back to the correct point by turning the
distributor, but the valve timing will still be wrong and it won't run.

 

Well, I don't think it looks like a jumped timing chain. The motor
has no external timing marks on the crank anywhere that I can see, so
I pulled the number one plug, and felt the piston rise to TDC as I
turned the motor. The Rotor was pointed 180 out from #1 on the
distributor, so that would appear to be good...

I know we've got spark because I pulled the coil wire out and had good
strong spark evident. Rotor is turning.... Next I guess I'll look at
a fuel filter.

 

your timing mark for the crank might be inside on the crank gear, right
where the chain goes on. that's the way it is on the 3.5 but not sure on
the 3.9L

I'd be curious to know what stroke your piston was on when it came up. did
you have a valve cover off to verify the valves were closed or open on the
exhaust side?

Well, I don't think it looks like a jumped timing chain. The motor
has no external timing marks on the crank anywhere that I can see, so
I pulled the number one plug, and felt the piston rise to TDC as I
turned the motor. The Rotor was pointed 180 out from #1 on the
distributor, so that would appear to be good...

I know we've got spark because I pulled the coil wire out and had good
strong spark evident. Rotor is turning.... Next I guess I'll look at
a fuel filter.

 

Chrysler LA v8s (from which the 3.9 is derived) have the timing degree
marks on the timing case at the front of the engine, and a single slot
on the harmonic balancer is the pointer on the crank.

 

I know from my Haynes manual that there are marks inside on the crank
and cam gears, but that is not something I want to disassemble to get
to. Lets see... PS pump, alternator, smog pump, water pump all need
to come off.... Not something I want to undertake casually.

As to how I know what stroke my piston is at, I was at TDC on the
exhaust stroke, since my distributor was 180 out from number 1. It's
got to be one or the other, either TDC at on the compression stroke
with distributor pointed at #1, or as I found it...

Now, that doesn't mean I couldn't be just one tooth off, which could
probably prevent starting. After I validate that I've got proper gas
flow to the carb, the next step would be to pull off the valve cover
on one side and observe how the valves are situated when they come up
on TDC of the exhaust stroke...

 

Its not that bad, really.

But you should still find the slot on the harmonic balancer and make
sure it aligns within a few degrees of the O degree mark on the timing
cover. You'll have to clean away some dirt and grime to find them, but
given that this is an 88 carbureted 3.8, the whole front of the engine
should look EXACTLY like an '88 318 v8.