GamblerSeanAZ
Member
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.
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.