1988 5th sputtering, shaking, popping after Lean Burn delete

GamblerSeanAZ

Member
Joined
Apr 14, 2020
Messages
23
Reaction score
10
Location
Phoenix, AZ
Long time lurker, first time poster. The short version is that I bought a $500 1988 5th Ave on FB Marketplace, replaced the computer control and carb, and I'm having some driveability problems. Read on for the long version. Thanks in advance for reading and replying.

Brief history:
The car is a 1988 Chrysler Fifth Avenue, originally with the Holley 6280 electronic carb and electronic spark control on the 318. When I bought the car, it was running super rich, and puffing black smoke from the exhaust. It had no power, and stumbled when you tried to accelerate. It did manage to get up to 65 on the highway, and I successfully drove it 30 miles home. I didn't want to troubleshoot the computer/electronic control systems, so I removed the computer and air cleaner, carburetor, and distributor. I've left all wiring and connectors intact for now. I replaced the factory carburetion and ignition components with the following:

Holley 2300 500 CFM 2bbl (PN 4412) on a Speedway Motors adapter (PN 1351934)
Spectra Premium distributor with vacuum advance (PN CH04)
AC Delco 4-pin GM HEI module (PN D1906)
AC Delco GM ignition coil (PN BS3005)
Standard Motor Products spark plug wires (PN 10117)
NGK GR4 V-power spark plugs (PN 2635)

The ignition module gets its voltage source from the B+ terminal on the alternator, via a Bosch-style relay that is triggered from a wire from the electronic spark control harness (a fat pink or blue wire, I don't remember which) that is hot in key run and key start positions. The carburetor is straight from the box, no adjustments as of yet. The only vacuum lines going to the carb are for the distributor's vacuum advance, and the PCV valve, which I also replaced. I installed the distributor, and set initial timing to 12 degrees BTDC.

The problem:
The car starts and idles fine, and revs nicely through the RPMs IN PARK. On the road, IN DRIVE, it idles fine, and runs fine with the throttle just barely cracked. If I roll onto the gas pedal to accelerate briskly, or try to hold speed up an incline, the car shakes, the engine sputters, and if I don't back off, it will pop and sometimes stall. I believe it's popping through the carburetor, but I'm not sure.

Troubleshooting:

Compression - I did a cold, dry compression test. I held the throttle open, and removed one plug at a time to check compression. I see a 14% difference between the highest and lowest cylinders. I don't think this helps solve the problem. Anyway, here are the results:
1: 163
2: 143
3: 161
4: 150
5: 149
6: 140
7: 150
8: 158

Vacuum leaks - I sprayed all around the carb and intake manifold with carb cleaner with the engine at idle, and didn't notice any changes in the engine idle speed or characteristics. I don't think I have a vacuum leak.

Fuel pressure - fuel pressure stays around 6-6.5 PSI consistently, and doesn't change when the engine starts to sputter. I don't think I have a fuel delivery problem to the carb.

Accelerator pump - I looked down the carb while snapping the throttle with the engine off. I get a nice fat stream of fuel from the accelerator pump discharge nozzle.

Plugged cats - I removed the exhaust at the output of the exhaust manifolds, and the problem still persists. The catalytic converters aren't plugged.

Manifold vacuum - engine pulls 21-22 in-Hg at idle. In park, when I snap the throttle, the vacuum briefly drops, then rises and stabilizes as I think it should. In drive, with the throttle barely cracked, the motor still pulls 21-22 in-Hg. When I roll on the throttle and the engine sputters, vacuum drops to around 5 in-Hg. I don't know if the vacuum drop causes the sputtering, or if the sputtering causes the vacuum to drop.

Timing - I hooked the timing light back up to verify my initial timing. I noticed a few strange things about the way the light behaves. It seems to skip flashes in a random pattern. Also, the tach signal seems to be spotty and sometimes inaccurate. Weird. I noticed this when I first installed the distributor and initially set the timing, too. In an attempt to see if the light itself is damaged, I hooked the light up to my Aspen (1980 slant 6, with same GM HEI module and coil), and it flashes normally, and the tach signal is steady and seems accurate.

Summary:
I can't find anything specifically wrong to explain the sputtering and popping. The strange behavior of the timing light makes me think that maybe something weird is going on with the ignition system, but then why does it run so well in park, and only act up under load? I haven't done any carb adjustments, and I don't have a wideband O2 meter to monitor the true mixture, so I haven't addressed any carburetor or mixture-related possibilities.

Can anybody offer suggestions on what I should check next? Pic for interest.

93237942_224037235682538_8166266614057009152_n.png
 

Mikes5thAve

Well-Known Member
Joined
Mar 3, 2020
Messages
1,375
Reaction score
539
Location
Canada
You might need to adjust the carburetor a bit.
Where do you have vacuum for the distributor hooked up? It should be a ported source that has no vacuum at idle, but you should also leave that disconnected until you have this problem figured out.
The timing being irratic could be a result of the rough running and not the cause of it. A worn timing chain or even something from the power source you have the HEI hooked up to can cause the timing fluctuation. You should be able to connect it directly to one of the keyed power sources in the engine wiring. I think it's a dark blue wire but it's been a while. Or directly back to the starter relay. The HEI can also cause strange problems when there's something wrong with it. I've always used the normal mopar ignition parts.
 

Aspen500

Well-Known Member
Joined
Feb 14, 2015
Messages
7,030
Reaction score
2,759
Location
Rib Mountain, WI
Going by your description, I'd SUSPECT a fuel problem. Sounds like it's starving for fuel. You'd need to put a fuel pressure gauge in line and drive it to see if the fuel pressure stays good (roughly 6 psi). Another possible is the float level is too low. Idle and no load might be OK but with a load on accel, could cause a lean condition. Popping, backfiring, etc usually indicates the mixture is very lean more than an ignition problem. Not saying it isn't an ignition problem, only that you need to verify the fuel system first.

When you open the throttle, especially under load, the vacuum drop is normal. AT WOT (theoretically) the vacuum reading would be zero or very close to it. In reality, it'll be a bit higher than zero but you get my meaning.
 

GamblerSeanAZ

Member
Joined
Apr 14, 2020
Messages
23
Reaction score
10
Location
Phoenix, AZ
Going by your description, I'd SUSPECT a fuel problem...

Thanks for the suggestions. I did check fuel pressure in line to the fuel inlet on the carburetor, and it stayed between 6 and 6.5 PSI. The only carb I've ever played with is the Holley 1941 that came on my Aspen, so looks like I have some reading to do on the 2300. I'll read up on how to check the float level and report back.
 

GamblerSeanAZ

Member
Joined
Apr 14, 2020
Messages
23
Reaction score
10
Location
Phoenix, AZ
You might need to adjust the carburetor a bit.
Where do you have vacuum for the distributor hooked up? It should be a ported source that has no vacuum at idle, but you should also leave that disconnected until you have this problem figured out.
The timing being irratic could be a result of the rough running and not the cause of it. A worn timing chain or even something from the power source you have the HEI hooked up to can cause the timing fluctuation. You should be able to connect it directly to one of the keyed power sources in the engine wiring. I think it's a dark blue wire but it's been a while. Or directly back to the starter relay. The HEI can also cause strange problems when there's something wrong with it. I've always used the normal mopar ignition parts.

Thanks for the suggestions. I hooked the vacuum advance to both timed and manifold vacuum to see what would happen, and it didn't change anything. Regarding the possibility of an erratic power source for the HEI, that's why I grabbed its power from the B+ terminal on the alternator - it should be the best place for it. I'll put a DMM on the B+ line, and also the relay trigger and watch the voltage as I road test. I do have a new spare HEI module that I can try out also. Maybe the one bad apple in the bunch is the one they sent to me :D
 

BudW

Moderator
Staff member
Joined
Mar 4, 2012
Messages
5,121
Reaction score
1,485
Location
Oklahoma City
Two things jump out at me.
First is the port for vacuum advance. It should have nothing at or off idle and good vacuum at higher RPM.
You said you already checked that – so I will go on.

Timing jumping around concerns me. All but the cars with HD engines (which mostly means better bearings inside torque converter and roller timing chains) came with plastic (single roller) timing chains – which are quieter and cheaper to make. The bad side is they wear out – quicker than expected.
I would bet your timing chain is not in good condition.

It is not hard to check. Remove the distributer cap and push away enough to see the rotor. Get a 1¼” socket and ½” drive ratchet and insert onto the crankshaft balancer bolt. It might help to have a second set of eyes, at this point. Rotate the crankshaft one direction about ¼ of a turn and Stop. Set the ratchet direction to the other direction - but don't rotate yet.
Now, with someone watching both the ratchet and the rotor, when you turn the ratchet - the rotor should also turn at exact same time. If it doesn't, then you have timing chain wear.
The amount of wear can be measured by how far the ratchet turns before rotor moves. 1-2 degrees is not much. 15-20 degrees is WAY WAY TO MUCH! Much more play more than that = timing chain is about to jump time. “Jump time” means you will need to get the sneakers out of the trunk and start walking home (if you catch my drift).

Hardly anyone sells the plastic timing chain gears anymore – because of they wear out too fast. Get a good quality double roller timing chain and you will be set for a long time. If you are going the trouble to change the timing chain, I would also spring for a timing chain tensioner.

2843610 Plastic TC.jpg

Plastic single roller camshaft sprocket (plastic teeth on an aluminum gear)
318 Plastic TC a.jpg

This is one on a small block. I have seen teeth worn to dimples OR where teeth break completely off.

318 DR TC.jpg

A all-metal double roller timing chain. You get what you pay for (ie: levels of quality)– so budget accordingly.

small block tensioner.jpg

A simple bolt on timing chain tensioner – available through Mopar Performance or aftermarket. This is well worth the investment - if you plan on driving the car much. This will work with any double or single roller timing chain or even (gasp) plastic.

BudW
 

GamblerSeanAZ

Member
Joined
Apr 14, 2020
Messages
23
Reaction score
10
Location
Phoenix, AZ
Two things jump out at me.
First is the port for vacuum advance. It should have nothing at or off idle and good vacuum at higher RPM.
You said you already checked that – so I will go on.

Timing jumping around concerns me. All but the cars with HD engines (which mostly means better bearings inside torque converter and roller timing chains) came with plastic (single roller) timing chains – which are quieter and cheaper to make. The bad side is they wear out – quicker than expected.
I would bet your timing chain is not in good condition.

It is not hard to check. Remove the distributer cap and push away enough to see the rotor. Get a 1¼” socket and ½” drive ratchet and insert onto the crankshaft balancer bolt. It might help to have a second set of eyes, at this point. Rotate the crankshaft one direction about ¼ of a turn and Stop. Set the ratchet direction to the other direction - but don't rotate yet.
Now, with someone watching both the ratchet and the rotor, when you turn the ratchet - the rotor should also turn at exact same time. If it doesn't, then you have timing chain wear.
The amount of wear can be measured by how far the ratchet turns before rotor moves. 1-2 degrees is not much. 15-20 degrees is WAY WAY TO MUCH! Much more play more than that = timing chain is about to jump time. “Jump time” means you will need to get the sneakers out of the trunk and start walking home (if you catch my drift).

Hardly anyone sells the plastic timing chain gears anymore – because of they wear out too fast. Get a good quality double roller timing chain and you will be set for a long time. If you are going the trouble to change the timing chain, I would also spring for a timing chain tensioner.

View attachment 39957
Plastic single roller camshaft sprocket (the part of which is plastic, on an aluminum gear)
View attachment 39958
This is one on a small block. I have seen teeth worn to dimples OR where teeth break completely off.

View attachment 39956
A all-metal double roller timing chain. You get what you pay for (ie: levels of quality)– so budget accordingly.

View attachment 39959
A simple bolt on timing chain tensioner – available through Mopar Performance or aftermarket. This is well worth the investment - if you plan on driving the car much. This will work with any double or single roller timing chain or even (gasp) plastic.

BudW

I commend you on the very thorough explanation. Thanks for writing that up. I'll add timing set wear to my list of items to check, and report back.
 

Aspen500

Well-Known Member
Joined
Feb 14, 2015
Messages
7,030
Reaction score
2,759
Location
Rib Mountain, WI
I double the tensioner thing. My Dakota (3.9L Magnum) has an timing chain rattle at idle since the beginning of time (meaning since new). A couple years ago at around 160,000 miles I decided to replace the chain just as mental insurance. At the time, I added the tensioner and it's dead silent at idle. The 3.9 was infamous for the chain rattle, which is why it became standard production in 1997. Mines a '96 so, didn't have it. Best part is, since Chrysler doesn't change things for no reason, it retrofits V-6 and small block V-8 back to very early (guessing to the '57 318), including LA and the old poly head 318, and possibly even SOME Gen 1 Hemi engines of the 1950's, which use the same chain as the poly, LA and Magnum engines. Another reason to love Mopar's!
 

AJ/FormS

Well-Known Member
Joined
Apr 26, 2016
Messages
1,291
Reaction score
305
Location
On the Circle of the earth, Southern Man,Canada
If your timing light is jumping around,
AND dropping sparks,
AND sparking at the wrong times,
AND,your timing chain is not that bad;
Then;
of your D has a magnetic pick-up in it, then;
I'll bet the polarity of the trigger is reversed.
When this happens, the coil gets fired on the falling side of the signal, which at idle seems to work. But as the Rs rise , the signal becomes highly unstable, and the erratic timing light strobing is the proof..
 

GamblerSeanAZ

Member
Joined
Apr 14, 2020
Messages
23
Reaction score
10
Location
Phoenix, AZ
If your timing light is jumping around,
AND dropping sparks,
AND sparking at the wrong times,
AND,your timing chain is not that bad;
Then;
of your D has a magnetic pick-up in it, then;
I'll bet the polarity of the trigger is reversed.
When this happens, the coil gets fired on the falling side of the signal, which at idle seems to work. But as the Rs rise , the signal becomes highly unstable, and the erratic timing light strobing is the proof..

The distributor indeed has a magnetic pickup. I swapped the trigger leads on the ignition module, and the car wouldn't start. Should I assume that I had them hooked up properly in the first place? Or is it more complicated than that?
 

GamblerSeanAZ

Member
Joined
Apr 14, 2020
Messages
23
Reaction score
10
Location
Phoenix, AZ
The distributor indeed has a magnetic pickup. I swapped the trigger leads on the ignition module, and the car wouldn't start. Should I assume that I had them hooked up properly in the first place? Or is it more complicated than that?

Quoting and replying to myself o_O

I don't think I can simply swap the trigger leads and expect the car to start. If indeed I'm triggering off the falling edge of the tooth, and then I swap the trigger leads, I've advanced the timing by the number of degrees that the tooth is wide, and now the timing may be so far advanced as to cause hard starting. I need to swap the leads and retard the timing to test this theory. Hopefully I have time to play with it today.
 

Mikes5thAve

Well-Known Member
Joined
Mar 3, 2020
Messages
1,375
Reaction score
539
Location
Canada
I don't remember magnetic pickup ever making a difference if the leads are reversed. It works or it doesn't.
I'm still thinking it's at least partially a carb related problem. It could also be a defective HEI unit. Did you check the air gap of the pickup in the distributor? usually that doesn't cause problems as long as it's not set too wide.
 

Camtron

Well-Known Member
Joined
Apr 25, 2019
Messages
1,814
Reaction score
1,376
Location
US
Sounds like general retarded timing and/or a lean carb by the symptoms mentioned in the OP, but the erratic timing is an interesting point. Wonder if your ignition module is bad if not a blatant worn out timing chain. Sure you don’t have the #5 and #7 spark plug wires mixed up or something like that? That would also cause the symptoms you’ve described.
Best of luck.
 

BudW

Moderator
Staff member
Joined
Mar 4, 2012
Messages
5,121
Reaction score
1,485
Location
Oklahoma City
Reversing the pickup coil leads will cause issues, As the reluctor rotates to/from the pickup coil, a small bit of A/C electrical current is produced. The ECU looks for a rise in voltage to trigger the ignition coil. By reversing the leads, the A/C current generated by the pickup coil will have voltage reversed thereby not triggering the ignition coil until later the in crank/distributor rotation (40 degrees crank rotation later?).

The wires in harness going to ECU will have one wire gray (or black) and other wire will be orange (or yellow or red).
BudW
 

GamblerSeanAZ

Member
Joined
Apr 14, 2020
Messages
23
Reaction score
10
Location
Phoenix, AZ
If your timing light is jumping around,
AND dropping sparks,
AND sparking at the wrong times,
AND,your timing chain is not that bad;
Then;
of your D has a magnetic pick-up in it, then;
I'll bet the polarity of the trigger is reversed.
When this happens, the coil gets fired on the falling side of the signal, which at idle seems to work. But as the Rs rise , the signal becomes highly unstable, and the erratic timing light strobing is the proof..

YOU WIN!!! That was the problem! I swapped the leads at the ignition module, and got it started. Timing was way far advanced after swapping the leads, so I hooked up the timing light (which now flashes rock solid) and retarded it to 12 BTDC initial. Runs like a top now, and does nice 1-wheel peels from a dig :D. Thanks AJ/FormS! Also, thanks to everybody who offered tips and suggestions.
 

AJ/FormS

Well-Known Member
Joined
Apr 26, 2016
Messages
1,291
Reaction score
305
Location
On the Circle of the earth, Southern Man,Canada
Chit I forgot to tell you about resetting the timing; glad you got it figured out.

Now, about those one-wheel peels; that's a bad idea and enough of 'em will kill your rearend. Little by little and then, often, catastrophically. Get some bigger tires or a SureGrip, or whatever it takes.
 
Back
Top