Need help! 280SE 4.5 stumbles and won't go over 20mph

[Bezant]

Hi guys,

Re: timing, I timed it by vacuum and choosing the point with highest vacuum. It ran for 6000 excellent like that. This is with the dizzy advance connected.

Just to check when I reinstalled the dizzy I advanced to 5btdc, the issue remained. Actually the video is taken at that timing.

When I did pertronix I replaced the coil and disconnected the transistorized ignition.

The plug wires are

Karlyn-STI Spark Plug Wire Set; Push-On Style
P/N: 1161500018

The plugs are

Bosch Spark Plug; SuperPlus Heavy-Duty; Yttrium Electrode
P/N: 7900

[Graham]

Originally Posted by Bezant

Hi guys,

Re: timing, I timed it by vacuum and choosing the point with highest vacuum. It ran for 6000 excellent like that. This is with the dizzy advance connected.

Just to check when I reinstalled the dizzy I advanced to 5btdc, the issue remained. Actually the video is taken at that timing.

When I did pertronix I replaced the coil and disconnected the transistorized ignition.

The plug wires are

Karlyn-STI Spark Plug Wire Set; Push-On Style
P/N: 1161500018

The plugs are

Bosch Spark Plug; SuperPlus Heavy-Duty; Yttrium Electrode
P/N: 7900

I have also used vacuum to set initial timing. I would advance to max vacuum at idle, then back off slightly. Then check with light at idle and at 3000rpm. If you don't get advance to about 27 BTDC, then there is something wrong with the centrifugal advance in the distributor. Could be something preventing it from rotating or the weights are stuck. If you do get advance to ~27BTDC, then your problem is elsewhere.

If your car ran OK before, presumably Pert installation is good. It should be something like this (depends on switchgear type):


Have you removed and checked plugs are not fouled? Overly rich mixture could carbon them up. Those are resistor plugs. Some will say that is bad, but I ran with those for years with no problem. You can get NGKs without resistor if you ever change. Hopefuly Pertronix hasn't failed. They can.

[Bezant]

Originally Posted by Graham

I have also used vacuum to set initial timing. I would advance to max vacuum at idle, then back off slightly. Then check with light at idle and at 3000rpm. If you don't get advance to about 27 BTDC, then there is something wrong with the centrifugal advance in the distributor. Could be something preventing it from rotating or the weights are stuck. If you do get advance to ~27BTDC, then your problem is elsewhere.

If your car ran OK before, presumably Pert installation is good. It should be something like this (depends on switchgear type):


Have you removed and checked plugs are not fouled? Overly rich mixture could carbon them up. Those are resistor plugs. Some will say that is bad, but I ran with those for years with no problem. You can get NGKs without resistor if you ever change. Hopefuly Pertronix hasn't failed. They can.

Hi Graham,


I did get advance while revving.


The several of the plugs do get some carbon on them, nothing horrible, as I run rich (been chasing that for a while) but I cleaned all 8, no difference.


Would a failed Petronix still idle smoothly?

[Graham]

Originally Posted by Bezant

Hi Graham,
I did get advance while revving.
The several of the plugs do get some carbon on them, nothing horrible, as I run rich (been chasing that for a while) but I cleaned all 8, no difference.

Would a failed Petronix still idle smoothly?

Not saying this is your problem. Just theorizing :
A failing Pertronix could work better at lower rpm. At say, 700rpm, there may be enough time to energize the coil for a full spark but at 3000rpm there may not be enough time to get to 100% coil energy each time. So you get a weaker spark at higher rpm.

Do you have the original Pertronix 1885?

If your car won't go more than 20mph, there is something seriously wrong. Even something like not having all the plug wires going to the proper cylinders! (BTDT)

As mentioned before, you run on a different mixture circuit at idle that does not use the MPS. So make sure MPS checks out (test figures in manual). Also make sure it is getting manifold vacuum. In fact, you should do all the sensor and other tests in the manual (Section 07.4 - Part B of this link:http://www.oncebitter.com/r107/r107CD1/Program/Engine/107/M117_45/074-040.pdf )

When you set your timing, do you have the A/C switched on or off? The standard setting at idle is, as Fonzi said, 5deg ATDC. This is with A/C OFF. If it is turned ON, vacuum to the distributor is automatically turned off. If you then set to 5deg ATDC, you will actually be retarded about 10-13deg more. Not good! For your car, I would set timing to TDC with vacuum on and A/C OFF. This assumes your vacuum switch (between throttle body and distributor) is working.

Fuel supply. You might try a test of your fuel pump (Do you have the original Djet pump or an aftermarket type?) Disconnect the fuel return line that exits the fuel damper (just after the fuel pressure regulator under hood) and lead a hose into a container (something with volume markings). Then attach a 12v supply to the pump in a way that you can supply 12V for 30 seconds. You should get close to 1L of gas in the container. If you don't the pump could be faulty or the filters are dirty.

I have been where you are - It will all come right, but it takes a lot of checking.

[Bezant]

I have Pertronix 1885, yes. Not sure how I would test its functionality at high rpm.

I did double check my firing order when I checked all the plug wires and spark plugs.

I'll check the MPS vacuum and do some sensor tests again.

The timing is AC off. I had it 10btdc as I had read 5atdc was an emissions setting that hurt fuel economy, and 10btdc was giving me highest vacuum. It ran 6000 miles like that so I'm doubting that is it, but I'm happy to set it back to 5atdc just for the sake of testing it.

I tested fuel PSI but not total supply.

[Graham]

Originally Posted by Bezant

I have Pertronix 1885, yes. Not sure how I would test its functionality at high rpm.

I don't know how either. Probably need a scope or something. By the way, do you have the Pertronix Flamethrower coil?

Fuel supply flow is important of course and you never mentioned if you have the original Djet pump.

Another fuel issue can be a partly blocked return line (usually inside tank) It can affect fuel pressure and therefore mixture too.

[Bezant]

I do have the original pump I believe.

Wouldn't a fuel pressure issue show up on my fuel rail with a test gauge?

[Bezant]

Clue or just quirk of my timing light? #1 and #2 go dark at higher revs. It seems to change slightly depending on where on the wire I'm at.

[Graham]

Originally Posted by Bezant

I do have the original pump I believe.

Wouldn't a fuel pressure issue show up on my fuel rail with a test gauge?

It would if you could run the engine at high rpms for long enough. Hard to do, I would think. If fuel pressure on rail is not affected when you rev engine up and down to say 3000rpm then this is not likely your problem. Getting enough fuel could be though.

If you can rev engine to 3000rpm to check advance, then question is - why won't it rev when on the road under load? Have you checked that the linkage from pedal does fully open the throttle plate? (grasping at straws here!)

[Graham]

Originally Posted by Bezant

Clue or just quirk of my timing light? #1 and #2 go dark at higher revs. It seems to change slightly depending on where on the wire I'm at.

Is distributor cap new or at least good? The Pertronix magnet can sometimes prevent the rotor from going fully down and it can score the contacts in the cap. Had this happen on one aftermarket cap I had.

[fonzi]

Originally Posted by Bezant

Clue or just quirk of my timing light? #1 and #2 go dark at higher revs. It seems to change slightly depending on where on the wire I'm at.

Looks like you have identified you’ve got a spark issue.


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[Bezant]

Ignition Coil!!! I put my old bosch on on a whim and it runs perfect.

[meltedpanda]

PM me and Ill send you some DJet diagnostic info. May help

[Benz Dr.]

Originally Posted by Graham

It would if you could run the engine at high rpms for long enough. Hard to do, I would think. If fuel pressure on rail is not affected when you rev engine up and down to say 3000rpm then this is not likely your problem. Getting enough fuel could be though.

If you can rev engine to 3000rpm to check advance, then question is - why won't it rev when on the road under load? Have you checked that the linkage from pedal does fully open the throttle plate? (grasping at straws here!)

I hook a fuel pressure gauge to the cold start line and then I run it outside of the engine bay where I tape it to the windshield. Easy to see and read.

I run about 10 degrees BTDC or 4.5 engines run like mutts.

[Graham]

Originally Posted by Benz Dr.

I hook a fuel pressure gauge to the cold start line and then I run it outside of the engine bay where I tape it to the windshield. Easy to see and read.

I run about 10 degrees BTDC or 4.5 engines run like mutts.

My fuel pressure gauge is permanently installed. See below. The other gauge is the wideband AFR gauge (for setting and monitoring mixture)

For timing, I set at about 0-5 BTDC to start, then adjust so I get about 27 BTDC at 3000rpm. I forget what it is at idle then, but probably about 5-8BTDC.