Thread: 92 Classic 3.9 Running Rough under load

Thanks for the input. I am stuck now until the weekend and hopefuly will have the 'bits' delivered tomorrow to fit Saturday. Will run through your suggestions whilst I am at it.

BTW, I believe a 5AM MAF will work on a 92 but not vice versa i.e. mine is a 3AM and a mate has offered to pull his 5AM so that I can test it on mine ?

Regarding the timing chain being a tooth out - no work has been done in this area prior to it deteriorating to its current poor performance. Maybe a bit of stretch in the chain ? Not sure that this explains the sudden drop in power after 3 weeks of not being used - sounds more like an electrical problem to me.

I will also pick up a compression tester and try that out over the weekend.

Thanks again. Maybe this is the excuse I need to start looking for a 4.6

Sounds like you have checked all the basics but have you checked the ignition module & pickup inside the dizzy? also could be the coil or a combination of both producing the exact same symptoms as my old Vogue 3.9. Basically was a VERY weak spark that sometimes could not detonate on some cylinders. would not start sometimes also

Ordered new ones an installed a Bosch GT40 coil & she purred after that

Ordered new ones an installed a Bosch GT40 coil & she purred after that

I hope you didn't as GT40 is a coil for points ignition. It will run with a amplifier but not as well as a correct coil.
Regards Philip A

Originally Posted by chang

Sounds like you have checked all the basics but have you checked the ignition module & pickup inside the dizzy? also could be the coil or a combination of both producing the exact same symptoms as my old Vogue 3.9. Basically was a VERY weak spark that sometimes could not detonate on some cylinders. would not start sometimes also

Ordered new ones an installed a Bosch GT40 coil & she purred after that

Not really sure how to check these......I am more than a little challenged in the electrical department ! I am looking at an ignition module for $75 although I am sure I can get this a little more cheaply? This will be fitted remotely for insurance. I will pull out the RAVE manuals and take a look at the other components in the dizzy. Coil might be the next option as these are relatively inexpensive.

Ultimately I want to refurbish as much as is practical. Old working bits can be kept as spares.

This is probably a good time to mention my Bosch ignition amp upgrade. Seems to fix many weak ignition problems...

Lucas ignition amplifier replacement by Bosch 024

Not a bad upgrade by the looks that one. Gt40 did work fine an I did not notice any difference between it an the Lucas coil when the Lucas was working but I'd have to agree with going genuine after I found out by using a non Gen ignition module an lasted about 2 weeks! Was not very happy. Genuine may be 200 but just think your original one lasted 20 odd years in a lot of cases so its well worth it. There is a way you can do it using a commodore 5l v8 ignition module to save money but once again I say don't touch it.. Buy a bosch oe coil an a genuine ignition module if you do

Thanks for the PM Bee Utey. I will look at this if my other remedies fail.

Received most of the new parts on Friday but not plugs & leads. As I had the new vacuum advance and replacement 3AM MAF (second hand but tested) I decided to strip down the airbox, remove the plenum for inspection and remove the dizzy.

I took the dizzy cap off, photographed the rotor position and removed the dizzy to inspect and clean. Stripped the amplifier and heat sink and got to the reluctor.

Firstly every external surface is covered in a rubbery film so I guess someone has given it a good waterproofing treatment in the past. Secondly there was no plastic cover under the rotor arm (& 3 screws missing) so everything was exposed. I'm not sure if this makes much of a difference, however what was immediately obvious is that I could see the rubber 'O' ring obove the reluctor meaning the circlip and washer had not been re-fitted previously.

So now I am trying to remove the reluctor (as per Hayes instructions) but it is stuck fast. I don't want to use too much force in case I bend/break something. Hayes suggest leverage with a small screwdriver tip but I think I am in need of a puller (any suggestions ?)

Also, as I am cleaning the outside casing I see an exposed hole big enough to poke my little finger in allowing me to view the mechanical advance mechanism (not the one for th evacuun advance). Should this be covered with a rubber grommet or something?

Lastly, as I downloaded the photos to my computer the picture is corrupt !!! this is the first corrupt file that I have had in over 6000 photo's !!!. As I will not be turning the motor at all I guess that the worst that can happen is that I am out by 180deg on refitting and I can pick this when the timing mark is close to TBC and the rotor arm is pointing to the opposite of no 1 cylinder lead ?

Originally Posted by bigdog

Thanks for the PM Bee Utey. I will look at this if my other remedies fail.

Received most of the new parts on Friday but not plugs & leads. As I had the new vacuum advance and replacement 3AM MAF (second hand but tested) I decided to strip down the airbox, remove the plenum for inspection and remove the dizzy.

I took the dizzy cap off, photographed the rotor position and removed the dizzy to inspect and clean. Stripped the amplifier and heat sink and got to the reluctor.

Firstly every external surface is covered in a rubbery film so I guess someone has given it a good waterproofing treatment in the past. Secondly there was no plastic cover under the rotor arm (& 3 screws missing) so everything was exposed. I'm not sure if this makes much of a difference, however what was immediately obvious is that I could see the rubber 'O' ring obove the reluctor meaning the circlip and washer had not been re-fitted previously.

So now I am trying to remove the reluctor (as per Hayes instructions) but it is stuck fast. I don't want to use too much force in case I bend/break something. Hayes suggest leverage with a small screwdriver tip but I think I am in need of a puller (any suggestions ?)

Also, as I am cleaning the outside casing I see an exposed hole big enough to poke my little finger in allowing me to view the mechanical advance mechanism (not the one for th evacuun advance). Should this be covered with a rubber grommet or something?

Lastly, as I downloaded the photos to my computer the picture is corrupt !!! this is the first corrupt file that I have had in over 6000 photo's !!!. As I will not be turning the motor at all I guess that the worst that can happen is that I am out by 180deg on refitting and I can pick this when the timing mark is close to TBC and the rotor arm is pointing to the opposite of no 1 cylinder lead ?

Ya should'a used a texta to mark the dissy. The dist will engage the cam gear but only engage the oil pump in a couple of positions, give or take a cyl or two... back to basics, remove no.1 spark plug, put timing pointer to TDC, determine firing point by blowing into no1 plug hole with a piece of heater hose. back pressure = firing, no back pressure = 1 revolution out.

To remove the reluctor use two screwdrivers and rock it gently. Never failed me yet.