stutter between 4000 and 5000

[mycastle]

Have a 78 SC with an 82 CIS. Runs strong, but lately has been stuttering as I accelerate through the 4000 range. Rapid acceleration it stutters once, gradual acceleration, it stutters several times. smooth below 4000 and above 5000. same symptoms in 1st, 2nd, 3rd, and 4th gear.

Today i noticed a deep base tone (not very loud) while it was stuttering, almost like it was trying to backfire.

Am I getting predetonation? where to start?

I have vacuum advance, hoses look good.

Read somewhere that the plate in the distributor could be hanging up and that lubricating it would be a potential cure.

Just starting the journey to finding and fixing this problem - appreciate the insight.

[Pato911]

Hmmmm, maybe not the same but I got rid of a stutter by replacing plugs and wires.

[NoYouRelax]

I have the same exact problem and have that deep base sound too on my '83. I might have oil carry over due to adding too much after an oil change, I am checking for fouled plugs tomorrow and see if the timing has drifted. Plugs and wires have 7000 miles.

I will let you know if I find a smoking gun.

[mycastle]

I have about 15000 on this rotor/cap/plugs/wires and the last time the valves were set. Getting ready to commit to checking the valve clearances and replacing the rest. The rotor and cap has some markings but I have seen worse that worked fine before.

confusing as to why it starts at 4000 and is gone at 5000. The low base rumble is definitely attempted backfiring - heard it clearly today - keeping her under 4000 until I figure this out.

[gerben1986]

Did you check for airleaks etc? That could be the cause of this, CIS is very sensible for air leaks...

[mycastle]

Interesting thought on the air leak and I have not checked for any yet - I may be erroneously thinking that an air leak is a low probability cause in this case because I would think an air leak would manifest itself over a wider range of operations.

Right now the symptoms are strictly present between 4000 and 5000 rpm. I am focusing on the distributor for now as I believe there is something mechanical that is effecting the timing. Saw a good thread on distributor cleaning - will walk down that path this weekend and see what fruit that bears.

[DRACO A5OG]

Try this.

Place the engine to TDC and remove the dizzy.

Check for slop as you rotate/spin it. Does it wobble? if so at 4-5K RPMs that may be the cause of the miss-fire. the contact's of te dizzy to cap not making contact.

How does the cap look, any signs of abnormal wear or gouging?

[gerben1986]

Originally Posted by mycastle

Saw a good thread on distributor cleaning - will walk down that path this weekend and see what fruit that bears.

Could you point us/me also to that thread about distributor cleaning?

[NoYouRelax]

mycastle I found my problem to day as I started with the spark plugs....not a fan of ths task! I did the 4, 5, 6, cylinders first and when I got to the other side I found 2 wires backing out, barely connected to the spark plug if at all, but enough contact at low RPMs. So I basically had 4 cylinders firing at 4000 rpm. I hope this helps because that deep base tone is the engine dragge a cylinder or 2 that is just not firing.

I hope you stumble across something so obvious. I wonder if wires caan back out over time or they were never really seated right.

PS.. what a PIa that 6th cylinder plug can be!

[mycastle]

due to life distractions didn't make it to pulling the dizzy yet, but I can slip out and pull some spark plug wires easy enough - I will go check that. I had earlier just checked seating, but I didn't challenge the wires themselves.

[mycastle]

Here is the link to pulling and cleaning the distributor

Distributor service (Clean and lube) real easy without removing the pinion gear!

[mycastle]

Checked timing before I pulled the distributor - appeared to be good - 5 BTDC at idle with vacuum hoses removed - hard to tell where it was at the high end - doesn't appear that there is a mark there - will look closer after I re-install the distributor.

Pulled distributor - wire going to pick up coil has insulation damage and you can see the shield wire - shouldn't be a problem, but will put some tape over it before I reinstall.

HOW important is the felt piece? didn't see one when I pulled roter off.

Had a little scare pulling the three "hex head" bolts out - they were phillips head and one stripped - had to drill and extract - looks like it came out clean, but now i need to three hex head bolts - off to tacoma screw tomorrow.

Overall the distributor looked fairly clean - so it doesn't appear that this is my problem. Will reassemble once I get replace cap bolts and see what I can do with getting the timing set.

While I was in there I traced out the two vacuum lines - both lines appear flexible and in tact.

[mycastle]

Started right up after distributor reinstall (whew). Set timing at 5 BTDC with vacuum hoses removed. brought it up to about 4000 RPM and it stalled, backfired, and died.

Several restart attempts and then repeated the stall/backfire/die trick.

I had the air filter and cover off - could have been the problem - after I installed those it started up and I was able to bring the rpm up to around 5000 with no issue.

So i took it for a test drive - slow moving out of the residential area. got to a 45 mph road and accelerated up in 2nd gear - got to 4000 and it started sputtering and back firing.

Now I am confused - it didn't do it cold, but warmed up it did - I am now looking at components that change state when heated (WUR/AAR/ etc.) - also now looking for a vacuum leak.

Question - I recently broke one of the two tangs that hold the air cleaner cover on - can that create enough air flow into the air box to cause an imbalance? It's all metered air going in so I wouldn't think so, but my initial startup challenges with the air filter removed tells me it might be.

[mycastle]

put new rotor and cap. same basic results. pulled 02 sensor wire - rpm jumped at idle to 1600. Car seemed to run little better. Still had some sputtering. Took it on the highway. it pulled hard from 2000 to 6000, shifted, pulled hard with a little sputter in the mid 4000, shifted, pulled hard.....

Turned around at next exit, sputtered and backfired as I entered highway. Basically, if i give it just enough peddle to accelerate - it goes smooth. to much peddle, it bucks. anything above 5000 rpm is strong and smooth.

Checked all connections (14 pin and lambda pin)

Wire on Distributor is damaged - could that be my problem?

[timmy2]

Post a picture of the distributor wire in question.


Sent from my iPhone using Tapatalk

[mycastle]

Here is the wire to the distributor

[mycastle]

Did some more playing and have two issues.......

1) at idle, pull both vacuum lines - no change in timing location..... is that right - I would have thought that at idle there was a vacuum retard happening.

2) by touching the distributor sensor the engine stutters or dies - I think I have a faulty connection where that wire is frayed.

So I looked it up on the parts line and found the replacement pigtail - only problem is is that mine is not a pigtail - it disappears into the bundle - is there a kit that can put a receptacle plug in that the pigtail connects to?

[timmy2]

You can cut your existing green wire and install a connector.
Lots of detail in this thread.
Read it all.

Distributor Green wire loose and frayed

[mycastle]

Thanks Dennis - did a lot of surfing on the green wire last night and am convinced that that is my smoking gun and it looks pretty straight forward - just need the green wire replacement.

Have you ever rebuilt an old connector? in other words, pull the connector and put a new coax on it?. I think I will include a trip to radio shack today and get some thin guage coax and try to frankenstien the connector back into life as a temporary fix until I get a new replacement one - I really need my car back on the road as it is my DD for the next couple of weeks while my Audi is OOS.

[mycastle]

Started my attempted temporary repair until i get a replacement green wire (need the car running this week)

in case there was any doubt, when I pulled the outer insulation off, here is what I saw.



looks like I just might be able to get some heat shrink over the center conductor to prevent shorting and then wire in.

And this can only be temporary as upon further inspection the connector itself is cracked and deteriorating