Need ideas to diagnose lack of top end power 4.5

[vandor]

OK, to clear it up, it seems like it's both rpm and load related. The higher the rpm, the sooner it happens. Of course I would not say 'high' rpm, as I'm sure at 60-65 mph the engine is below 3000 rpm, and it seems to be worst there.

No progress yesterday or today, as I pulled the AC compressor and today bought a new one and my free time was gone with that.

I'll try to answer everybody:

>By dwell method, I presume you mean the angle that each set of points stays open or closed?

Yes.

>I presume you wired Pertronix just as a points replacement if you are still using a Bosch Blue coil? That would mean that the MB switchgear is still in place.

Yes, but it's no longer getting a signal from the points. Pertronix instructions do not mention removing them. I checked and there is 12V at the coil.

>Have you checked vacuum at idle?

No, as I am mostly interested in getting the ign timing right at higher rpm, not at idel.

>What would happen if car has a vacuum leak. Would that affect high speed performance?

At wide open throttle the intake manifold is at nearly atmospheric pressure, so a vacuum leak would have little to no effect, IMO.

>Sounds like your trigger points may be "Floating" at higher RPMs.

But it's not only rpm related, it just gets worse the higher the rpm.

>Are both valve springs installed on each valve and are they broken or weak at all

They are there and not broken. Can't say if they are weak or not.

The plugs are NGKs that were recommended here. I'm 99% sure they are resistor plugs. It's cheap enough to try some non-resistor ones.

>If there was an ignition problem there would be backfiring as the unburnt fuel in the exhaust system ignited.

True. There is no backfiring.

> Maybe your fuel pressure is dropping.

Both pressure and volume tests were fine, and the pump does not 'know' that the engine is under more load - simply less fuel gets back to the tank. It does feel like that kind of problem, tho.

>Does the problem happen in every gear at a certain RPM?

It seem like the higher the gear the lower the rpm where it happens. Of course in the higher gears the engine has to work harder just to move the car, so there is more load on it to begin with.

>Speaking of rev limiter, do you maybe have a rev limiter rotor Csaba?

I changed it out to a non-rev limited one during the rebuild.

>You're positive that your coil is up to snuff with the pertronix?

No, I'll have to swap in another coil. We carry the Pertronix ones at work, so that'll be the easiest.

>So, this problem is not related to rpm's, but speed?

Seems both.
>Have you tried revving up in parking?

Yes, it's fine. I revved it quite a bit when I was checking max advance.

> Why dont you get the pert coil and bypass the switchgear?

Will do.

>is it a proper D-jet pump?

It looks like one.

>Hopefully the injectors are clean and not the problem.

I had them cleaned/checked while the engine was apart.

Thanks guys! It may be Thursday before I can make more progress as tomorrow is a busy day.

Csaba

[Tony H]

I know it seems extreem but time is money and it might be worth a dyno session to diagnose the problem.

[Graham]

>I presume you wired Pertronix just as a points replacement if you are still using a Bosch Blue coil? That would mean that the MB switchgear is still in place.

Yes, but it's no longer getting a signal from the points. Pertronix instructions do not mention removing them. I checked and there is 12V at the coil.

The instructions that came with my Pertronix were not correct. You should be using the Pertronix I part 1885 (not the II or III)

If installing as just a point replacement, all that is needed, is:

Red wire to ignition switch side of 0.4ohm resistor (12v supply)
Black wire to connecter that green distributor wire used to connect to.
Add a ground from distributor body to any good ground point
Make sure the Pert magnet is properly seated and allows the rotor to go fully down. (others had problems with this)
Pictures here (Pert wires are ones with blue connector insulation):

If you decide to eliminate MB switchgear and install Pert Flamethrower coil (Part 40011) wiring should be per pic below:

[vandor]

Hi Graham,

Is it now enough that I verified that the coil (and therefore the Pertronix) is getting 12V while idling? BTW, it is kit 1885.
What if I just connect the wire coming from the ignition switch directly to the coil + with the Pertronix connected to both sides of the coil?
We sell the kit for Fiats and all one does it connect the black to the coil negative and the red to the coil positive terminal.

Good idea on the ground wire for the distributor, I'll have to do that.
Thanks,

Csaba

[Graham]

Originally Posted by vandor

Hi Graham,

Is it now enough that I verified that the coil (and therefore the Pertronix) is getting 12V while idling? BTW, it is kit 1885.
What if I just connect the wire coming from the ignition switch directly to the coil + with the Pertronix connected to both sides of the coil?
We sell the kit for Fiats and all one does it connect the black to the coil negative and the red to the coil positive terminal.

Good idea on the ground wire for the distributor, I'll have to do that.
Thanks,

Csaba

The coil is the wrong place to connect the Pertronix. By the time you get to the coil, you have gone through two resistors and the Switchgear transistor circuit. See attached diagram.

If you don't have the red Pertronix wire connected as shown in pics (to wire from ignition switch near 2), and the black wire to where the green wire was (terminal 7), change them and see what happens. Your problems may go away

[vandor]

So the Pertronix is used to signal the original module?
I had lengthened the Pertronix' wires so they reach the coil.

Csaba

[Graham]

Originally Posted by vandor

So the Pertronix is used to signal the original module?
I had lengthened the Pertronix' wires so they reach the coil.

Csaba

I may have misunderstood just how you have the Pert connected.

If you retain the switchgear then yes, Pert does same job as points did.

If you have bypassed the MB switchgear as in the hand drawn diagram a few posts back, the Red goes to coil + and Black to coil negative. But then you should use the Flamethrower coil.

[vandor]

This afternoon I changed the wiring so the coil gets full voltage from the ignition switch. I test drove the car and while the problem is not totally gone, it's not nearly as bad.
I was able to go 60 mph (~100 km/h) in 2nd gear, which would have been
impossible before. I was also able to accelerate uphill to over 80mph on the highway, while before it would start to miss around 70 on level ground.

Then I installed the Pertronix Flame thrower coil, replacing the Bosch blue coil. It did not make a difference.

The car runs well enough to drive safely now, so before I dig much further I will have to check the mixture, either with a wide band sensor, or on a dyno.
Thanks,

Csaba
72 280SEL 4.5

[Adv_rider]

Did you removed MB switchgear?

[Oskar]

at the firewall is a device to messure MAP.

On both my '71 W108, this device was drawing air. The seal between the 2 body halfes of that thing was the culprit.

It can be taken apart and the seal replaced ( some have screws, some are riveted. In case os rivets drillem out and put screws back )

Oskar

[vandor]

Hi Guys,

>Did you removed MB switchgear?

Bypassed it. It was not working before either, as it was not getting a signal, but the coil was getting voltage through a resistor.

BTW, I just read that the 3 ohm coil is not recommended for V8s, so I'll be getting a 1.5 ohm one.

>On both my '71 W108, this device was drawing air. The seal between the 2 body halfes of that thing was the culprit

Thanks Oskar, I will check that!

Csaba
72 280SEL 4.5

[Palolo]

Originally Posted by vandor

>Did you removed MB switchgear?

Bypassed it. It was not working before either, as it was not getting a signal, but the coil was getting voltage through a resistor.

Typically, once the pointless points are removed from the system, the resistors are not needed.

It is my opinion that they (the resistors) were introduced to lengthen the points' life and make the ignition "more reliable", since by then, the points were the weak link in the automotive chain.

Others may disagree and keep them in the system after upgrading the ignition (depending on the system used), but why lower the voltage at that point?

Good luck! Sounds like you are much closer.

pat

[WANT '71 280SEL]

With Pertronix installed, and the Pert coil, you shouldn't need the resistors.

Best Regards,

David

[Alastair]

One thing to remember with the D-Jetronic.....

Timing alterations will affect the Mixture of fuel supplied from the FI.

Make absolutely SURE the timing is correct throughout the rev-range from 1K to 5K or the fuel mixture will be incorrect.....

The D-Jet monitors the VACUUM in the manifold--and alters the Injector 'on' time to supply the correct amount of fuel--According to the amount of Vacuum present.

Timing --at any engine-speed if wrong, will seriously affect the Vacuum in the Manifold--and therefore, the Fuel to air Mixture.

The MPS is nothing like a 'standard' manifold/map sensor....

--Its basically a variable transformer --with the iron-core attached to a diaphragm. Its fed with pulses from that extra set of 'points' in the distributor....
--Mess about with the MPS--At your peril!

As you have altered the Ignition-system, I suspect That is the cause of incorrect Timing at different engine-speeds, hand hence, Wrong mixture. (Your 'lean' plugs)

[Graham]

Originally Posted by vandor

BTW, I just read that the 3 ohm coil is not recommended for V8s, so I'll be getting a 1.5 ohm one.

The 40011 coil I linked to just above the hand drawn wiring sketch in earlier post, is the correct one. It is 1.5 ohms.

Don't forget about adding a proper ground wire from distributor body.

Make sure your 12V source is from the front side of the 0.4ohm resistor - that is the wire from the ignition switch.

Check your idle vacuum - that will give you quick method of determining if you have vacuum leaks. Car should idle at about 16"Hg +/-. As previous poster said - recheck timing once you get Pertronix properly installed.