Engine Bogs and Misses Under Hard or Mild Acceleration

[CRW-FK5]

I have been having what appears to be a worsening condition in my 440 where under even mild acceleration the car stumbles and hesitates significantly.  If I push hard on the pedal, forget it.  It will kick back hard.  In addition to this, I cannot seem to get rid of a persistent ping.  I suspected perhaps a bad batch of gas, but it has been going on too long for that.  Backing off the timing does not effect the bog or get the pinging to go away either, even when at 8° BTC.  I have checked timing marks on balancer by setting up piston block in #1 and marking when piston stops in both clockwise and counterclockwise directions and confirmed that the distance between marks on balancer equal the factory mark.  I have replaced the aftermarket Edelbrock with another one with no difference.  I have pulled the distributor and checked for things like broken mechanical springs.  I have disconnected vacuum advance.  I have added 2 gallons off 110 fuel to full tank (this seemed to help reduce pinging but not eliminate it).

My engine did not behave this way a year ago, and seems to be getting worse.  I am running electronic ignition with chrome ECU.  Any ideas on what could be causing this would be greatly appreciated.

[c00nhunterjoe]

Lack of fuel pressure or a jumped timing chain.

[68 RT]

Lean, I would agree with above you are losing fuel pressure, fuel pump rod or bad pump.

[CRW-FK5]

Lean, I would agree with above you are losing fuel pressure, fuel pump rod or bad pump.

With a bad pump I would not expect an immediate reaction when I hit the pedal, since during initial acceleration the system should be pulling from full bowls.  If the hesitation occurred a few seconds later (due too bowl level reduction) I could see it being fuel delivery related.  I am leaning towards timing chain.  Is it possible to be able to adjust ignition timing back in with a jumped tooth, ending up with just valve timing off?  And with that, would I end up with the described performance issue?

[c00nhunterjoe]

Is the engine stock? Got alot of age on it?  It could still be a lean shot problem. Could be a wiped cam. Could be alot of things. I would start with fuel pressure 1st before pulling the timing cover. A compression test is another easy test and be my 2nd check.
   And no, adjusting ignition timing will not fix valve timing if it is a stretched chain. While not impossible, it is improbable. I have seen far more small block chevies jump time then big block mopars.

[BSB67]

  I have replaced the aftermarket Edelbrock with another one with no difference. 

Could you please expand on this

[CRW-FK5]

Is the engine stock? Got alot of age on it?  It could still be a lean shot problem. Could be a wiped cam. Could be alot of things. I would start with fuel pressure 1st before pulling the timing cover. A compression test is another easy test and be my 2nd check.
  And no, adjusting ignition timing will not fix valve timing if it is a stretched chain. While not impossible, it is improbable. I have seen far more small block chevies jump time then big block mopars.

Thanks.  I bought the car a little over a year ago so I'm not sure how tired it is.  I did, however, do a compression test on it last weekend and all cylinders are between 170 & 185 psi (cold engine).  The engine has decent street cam (Purple Shaft) and I believe at least 10:1 compression ratio.

Regarding the ignition timing, I did not mean to imply that I could correct valve timing by adjusting ignition timing, as I am aware that valve timing is determined by cam & crank sprocket position.  I wondered if perhaps I had jumped a tooth would I even be able to readjust ignition timing back to correct position.  If a jumped tooth would not allow ignition timing to be corrected then I could confirm that I did not jump a tooth.  Just a possible way to diagnose the problem without digging into it first, that's all.  Thanks for your  feedback.

[CRW-FK5]

  I have replaced the aftermarket Edelbrock with another one with no difference. 

Could you please expand on this

Sure.  I have a 750 Edelbrock on there now.  A friend had a 650 (or 600, not sure) Edelbrock that I put on just to see if the problem was carb related.  I got the same bogging with the other carb.

[68 RT]

You need to richen up the edelbrock, I had to do mine. Same problem you are having. Most edlebrocks are lean from the factory. Buy the strip kit it has everything you need. Mine had to go up 2 jet sizes on the primary and I think down on the metering rods. Also changed the metering rod springs. Very easy to do. Start with the springs. Also have you pulled any plugs to check for lean? 

[BLK 68 R/T]

Bad or loose magnetic pickup in the distributor?

[69_XS29L]

I had a similar problem many years ago on my 440.  Original stock ignition coil was faulty, start and run fine, but stumble bad or die under even light to moderate load. I'd check everything in the secondary ignition or high voltage side for voltage leaks, carbon tracking, opens or potential shorts before I threw any amount of money at the problem. Old school oscilloscope would be a good help.
Good luck, Mike

[CRW-FK5]

You need to richen up the edelbrock, I had to do mine. Same problem you are having. Most edlebrocks are lean from the factory. Buy the strip kit it has everything you need. Mine had to go up 2 jet sizes on the primary and I think down on the metering rods. Also changed the metering rod springs. Very easy to do. Start with the springs. Also have you pulled any plugs to check for lean? 

I do have the kit (#1489) and did try opening up the jets last year.  I also recall changing rods to richen up a bit.  No improvement but may not have been changing the right parts.  I didn't mess with the spring, however, so that's something I could try.  Which way would you go with them?  Towards lower in. Hg?  I've attached a picture of the springs below.  I think I have the colors correct but if you could confirm, that would be great.  From left to right, Blue (3"), Yellow (4"), Orange (5"), Pink (7"), Silver (8").

Regarding the plugs, they don't look lean to me.  Actually look okay.  See pictures below.

Thanks for your help.

[CRW-FK5]

Here is a picture of rotor position at TDC on #1.  I don't know how far off it would be if I had jumped a gear tooth but if it's significant I would think someone might be able to tell me if I'm off, relative to angle in picture.  To me it looks pretty close to where it should be, but would love to get confirmation.

[birdsandbees]

..sorry, that was with timing gear marks lined up.

(I had showed a picture that the rotor tip should point at the #1 cylinder with the timing gear dots lined up)

[CRW-FK5]

Yes.

[XH29N0G]

I think when the others are taking about jumping a gear, they are describing the timing chain and the timing on the cam (affecting valve timing).  This, as you said is different from the spark timing.  

Where the rotor points depends in part on how the distributor is installed so I do not think that will tell you whether the timing chain jumped.  

If the timing chain jumped, the only thing I can think of is either taking a look at the sprockets with the timing chain cover off to see if the timing marks line up or (better) determining where the lobe center is with a dial indicator.  I am not an expert in this and some who have answered already can provide clear information on whether what I have written is valid.  Both of these tests are possible, but fairly involved to do.


That said.  Your cold compression test does not strike me as crazy high though. 

[CRW-FK5]

I checked the play between crank gear and distributor and found it to be right around 7.5°.  Is this too much?

Picture below shows point (from 0° mark) where distributor rotor begins to rotate.

[CRW-FK5]

I think when the others are taking about jumping a gear, they are describing the timing chain and the timing on the cam (affecting valve timing).  This, as you said is different from the spark timing.  

Where the rotor points depends in part on how the distributor is installed so I do not think that will tell you whether the timing chain jumped.  

If the timing chain jumped, the only thing I can think of is either taking a look at the sprockets with the timing chain cover off to see if the timing marks line up or (better) determining where the lobe center is with a dial indicator.  I am not an expert in this and some who have answered already can provide clear information on whether what I have written is valid.  Both of these tests are possible, but fairly involved to do.


That said.  Your cold compression test does not strike me as crazy high though.  

Thanks.  Yes, but since the distributor is driven from the cam, both ignition and valve timing would shift if the chain jumps.  Ignition timing can be brought back in through adjustment to some extent, but obviously valve timing cannot.  I could have inadvertently brought ignition timing back in a while back not realizing I may have had a chain issue.  That was my thinking.

Relative to the distributor installation, the distributor can only be installed in 2 different positions, 180° apart, due to the slot in the bottom that drops into the gear.  So there is really no way I could have put the distributor in wrong without noticing it.

[XH29N0G]

I see your point.  (I mentioned the valve timing because I had a car where a timing belt slipped and it really behaved poorly - not detonation though). 

I do not know about the 7.5 degree play in the distributor, that doesn't seem right to me.  I hope you get this solved quickly.

[68 RT]

You need to richen up the edelbrock, I had to do mine. Same problem you are having. Most edlebrocks are lean from the factory. Buy the strip kit it has everything you need. Mine had to go up 2 jet sizes on the primary and I think down on the metering rods. Also changed the metering rod springs. Very easy to do. Start with the springs. Also have you pulled any plugs to check for lean? 

I do have the kit (#1489) and did try opening up the jets last year.  I also recall changing rods to richen up a bit.  No improvement but may not have been changing the right parts.  I didn't mess with the spring, however, so that's something I could try.  Which way would you go with them?  Towards lower in. Hg?  I've attached a picture of the springs below.  I think I have the colors correct but if you could confirm, that would be great.  From left to right, Blue (3"), Yellow (4"), Orange (5"), Pink (7"), Silver (8").

Regarding the plugs, they don't look lean to me.  Actually look okay.  See pictures below.

Thanks for your help.

Mine has the pink springs, maybe give them a try.

[BSB67]

I keep revisiting this post, and cannot help thinking there is something else we're missing.

Can you step back and give us a little history.  How long you've had it, how much you drive it, when did the problem start, has it always had a problem, what things have you done, are there any operating conditions that are okay, how does it idle....etc.

[CRW-FK5]

I keep revisiting this post, and cannot help thinking there is something else we're missing.

Can you step back and give us a little history.  How long you've had it, how much you drive it, when did the problem start, has it always had a problem, what things have you done, are there any operating conditions that are okay, how does it idle....etc.

Sure.  I have owned the car since February of '15.  I do drive it often, taking it to store on errands, etc...  The car idles okay but does have a higher street cam so some roughness is expected.  The car did not have the problem until around June of that year.  At that time I noticed when I got on it hard there was a significant stumble that only stopped when I backed off.  I had done nothing to the car prior to that that could be linked to it.  Nothing to engine.

The problem persisted and late last year I decided to buy the Edelbrock calibration kit to see if I could play around with jetting on the 750 (#1411) carb to try and cure it.  I tried larger jets in secondaries and smaller rods in primaries (I believe) but problem did not change.

Next I replaced fuel pump and filter, as they were fairly inexpensive.  No effect on condition.

Later on in the season I decided to swap carbs from the 750 cfm Edelbrock #1411 to a 600 cfm Edelbrock #1406 that a friend had laying around, just to see if the problem changed or went away.  It was an easy way to try and find the root cause.  As I mentioned, I did this late in the season so ambient temps were cool.  When I installed this and tested it the problem was gone.  I made sure the car was warmed up and tried several times, each time the bog or stumble was gone.  I then reinstalled the 750 and took it back out under exact same outside air temps and vehicle temps (done within 20 minutes of test with friends 600 cfm carb installed).  Immediately the bog / stumble was back.  I then believed that the issue was in the 750 carb, somewhere.  

Then I took the 750 carb and took it apart and cleaned it, blowing out passages, etc...  I also replaced the jet/rod configuration to what was installed when I got the car and confirmed they were to the recommended configuration in the Edelbrock guide, which they were.  I took the car out again (same day under same conditions) and the bog was gone.  At that point I believed the problem was solved and that perhaps I somehow had some dirt in the carb somewhere that was cleaned out during the R&R.  Since it was late in the season I put the car away for the winter content (so I thought) that the problem was solved.  

So this spring when I got the car out I found that the problem was back, and actually seemed a bit worse.  Outside temps were cool, similar to what they were late last season, so I do not believe that was the variable.  When I say worse, I mean now I just have to accelerate lightly and the stumble is there.  Before I had to really get into it.  So I swapped the same Edelbrock 600 back on, hoping I would see the same thing I did last year where the problem went away.  Instead, the problem continued.  So now it stumbles with either carb on it.

I know somewhere in the season last year (after the problem was found) I messed with the timing (using a timing light).  I just don't recall where it was but thought it was reading "after TDC", which did seem very odd.  I recall readjusting it but later going back in and readjusting again, thinking I may have had the zeroing dial on the light set accidently at some value other than zero when I read it before, causing me to think it was timed at a different degree than it actually was.  I have since confirmed that the ignition timing is set correctly (see above post).

I do have an AFR meter now installed and took the car out a few days ago.  Idling somewhat cold I am at between 12.7 -13.2, although it bounces around some.  At around 2,000 rpm (again somewhat cold) I am at 10.8 - 11.3.  Those seemed to be the ranges.  When warm and crusing maybe 1,500 rpm I am at 11.8 - 12.0, but when I then drop down a gear and accelerate moderately hard it steadily gets leaner peaking at 17.3 before I back off.  Another attempt I felt it begin to bog when it got to 13.8.  I have fairly new gas in it but could be some left over from last season and could be winter blend (although same gas as I had in it when testing late in season last year).  I have added 2 gallons of 110 racing fuel to try and get rid of pinging.  This did seem to help address that.

As mentioned above, I have had distributor out and disassembled.  No broken parts, springs, etc...  I have run compression test with good consistency between cylinders.  I have run leakdown test but believe the gauge was malfunctioning since repeated readings on same cylinder yielded varying results.  I did confirm in this test that valves are tight to the head and only loss is through rings.  I hear strong air hissing beneath the intake manifold area but believe it is the same sound from air blowing by rings and through block.  Leakage sound is identical for all cylinders.  Plugs were checked and seem fine.

I also checked angular play in the valve train, coming up with around 3.5°.  I did this by turning crank while watching distributor rotor and noting crank rotation when rotor just started to move.  At first I was at around 8° but noticed part of that was the play between distributor tab and gear slot.  So rechecking with this rotated to take up play I got around the 3.5° chain play.  This may seem like a lot but not sure it explains the severe bog I'm getting.

So this is pretty much where I sit today.  My next step is to try and go with different springs in the carb but can't help knowing that the car ran fine originally and that something changed, so any modifications to carb set up would either be unsuccessful or masking the root cause.  The timing oddity still makes me wonder about the whole thing.  Does it make sense that the timing light was reading ATDC?  Could that have been an indication that the chain had jumped a tooth?  I may have to explore that a bit more.

I really appreciate the help.  Thanks, all.

[BSB67]

Your problem is in the carb.  Fine tuning is not what is needed at this point, IMO.  You have a problem, you just need to find it.

[XH29N0G]

The others who are advising you know more than me so their comments should take precedence over mine, but in reading your description I have an observation and a question.

The observation:  If your air fuel is going to 17 and staying there on hard acceleration (rather than dropping back to ~13), you could have an issue with the main jets.  That could explain part of the issue with hard acceleration.  I think it should be in the 12-13 range for acceleration.  Also is the miss and bog in a specific rpm range and in all gears?

I also was curious where your timing is set (for idle and for total advance).

I also see you have a purple shaft cam, which one?  Am I correct in inferring that you have a manual transmission? 

[CRW-FK5]

.