Thread: Help with 3.5 V8 Ignition

Hello Michael,

If when you turn the ignition on (engine off) and measure the voltage at the ignition coil you see essentially 12 volts, then you do not have a ballast resistor and the Bosch GT40 is the correct coil. If on the other hand you measure anything from 6 to 9 volts, then there is a ballast resistor in the loom and the Bosch GT 40R is the correct coil.

If you use a 12 volt coil...the GT40 with a ballast resistor then the coil will not receive the voltage that it should to function correctly, so your plugs will deliver a weak spark.

If you use a 6 volt coil which is essentially what a GT40R is, and you use it without a ballast resistor, then the coil will work very well but only for a short time until it fails.

So, the GT40 is used without a ballast resistor, while the GT40R is used with a ballast resistor.

Hope this helps,
Ron.

Originally Posted by Michael2

My wifes 88 RRC [3.5V8] recently developed a fault where it fails to start when hot, but starts okay once it's cooled down.

She called me while I was at work, and with some over the phone diagnostics, I determined that the coil was very hot, so I bought a new one on my way home.

I replaced the coil GT40 (which I'd put in some months earlier) with the GT40R, which according to the pack, suits all RRs.

Which is the correct coil for the RRC?

I thought I'd fixed it, but it did it again. This time I turned up in the Defender and was able to ascertain that there was power to the coil, but no spark.

I replace the Ignition Module, but I could only get a 2nd hand one on a Saturday. Yes, I used plenty of heat paste.

Again the car stopped as soon as it got hot. Eventually my wife started it again and got it back home, where I was unable to start it. I ran the garden hose over the ignition module, and then it started fine.

It could be that the 2nd hand module is faulty, or that I'm using the wrong coil and heating it up.

I found the thread on using a remote ignition module, so this may be my next fix, but if I'm using the wrong coil, it would be easier to just get that right one.

Thanks in advance for your help.

- Michael

Please don't use a points type coil with this kind of electronic ignition. They are not designed to work there, their inductance is incorrect with your amplifier. The last person I told to do this didn't believe me because the local auto shop lackey (17 and pimply) said it was OK. Next time he came in and whinged about poor running I ripped it off and put the correct coil on, no further troubles!

I suggest you get an original coil, second hand if needed.

If you want an easily fixable High Energy Ignition conversion look at my post Lucas ignition amplifier replacement by Bosch 024

Originally Posted by RoverP6B

Hello Michael,

If when you turn the ignition on (engine off) and measure the voltage at the ignition coil you see essentially 12 volts, then you do not have a ballast resistor and the Bosch GT40 is the correct coil. If on the other hand you measure anything from 6 to 9 volts, then there is a ballast resistor in the loom and the Bosch GT 40R is the correct coil.

If you use a 12 volt coil...the GT40 with a ballast resistor then the coil will not receive the voltage that it should to function correctly, so your plugs will deliver a weak spark.

If you use a 6 volt coil which is essentially what a GT40R is, and you use it without a ballast resistor, then the coil will work very well but only for a short time until it fails.

So, the GT40 is used without a ballast resistor, while the GT40R is used with a ballast resistor.

Hope this helps,
Ron.

Thanks Ron, That seems to make sense. I get 12V at the coil with the ign on (motor off). But the Bosch Catalogue stipulates the GT40R.

I've never seen a ballast resistor in an EFI RR, and the voltage reading would suggest it's not there.

Could the GT40R perhaps better suit the electronic ignition?

Originally Posted by bee utey

Please don't use a points type coil with this kind of electronic ignition. They are not designed to work there, their inductance is incorrect with your amplifier. ...I suggest you get an original coil, second hand if needed. ...[/URL]

Is the GT40R soley a points type coil?

The Bosch Catalogue http://www.bosch.com.au/content/lang..._B_Sect(2).pdf
stipulates it for the electronic ignition Lucas EFI.

I'll check if I still have the original coil, but after 22 years and 450,000km I had thought that I should replace it to try to sort a rough idle problem some months back.

Originally Posted by Michael2

Is the GT40R soley a points type coil?

The Bosch Catalogue http://www.bosch.com.au/content/lang..._B_Sect(2).pdf
stipulates it for the electronic ignition Lucas EFI.

Michael ..... Just go with the flow ..........

Originally Posted by bee utey

I suggest you get an original coil, second hand if needed.

If you want an easily fixable High Energy Ignition conversion look at my post Lucas ignition amplifier replacement by Bosch 024

Mike

Michael2 wrote,..

Thanks Ron, That seems to make sense. I get 12V at the coil with the ign on (motor off). But the Bosch Catalogue stipulates the GT40R.

I've never seen a ballast resistor in an EFI RR, and the voltage reading would suggest it's not there.

Could the GT40R perhaps better suit the electronic ignition?

Hello Michael,

As you have 12 volts appearing at the coil, then the GT40R is not the correct coil to use as the R in the name advises that it is to be used with a ballast resistor. With a ballast resistor, 6 to 9 volts at the coil in the same situation is normal.

I think the best course of action is to either obtain a genuine Lucas coil of the specification that was originally fitted to your RR when new or compare the specifications to ensure compatibility.

Does your engine run a Lucas 35DLM8 distributor? If so, the matching coil is the Lucas DLB198.

Ron.

Just looked up the Bosch catalogue, I think the reference to GT40/GT40R coils is a publisher's mistake, very typical in Bosch catalogues. The reference is valid for the points RR entry only, the OE Bosch number changes for the EFI but not the stupid GT40 entries. Look above at the Discovery entry, never had pionts fitted and therefore no points coils recommended. Same ignition system!

This is just another example of dumb outsourcing. The last reasonably accurate Bosch catalogue came out in 1996 or thereabouts, I guard my copy jealously.

[QUOTE=bee utey;1180686Look above at the Discovery entry, never had pionts fitted and therefore no points coils recommended. Same ignition system!....[/QUOTE]

The 1988 RRC had Lucas Ignition and I think the 1989 came out with Bosch Ignition. That would mean that the Disco would have the Bosch system. I understand the points Vs electronic coils are different, but would there also be a difference between the Lucas Vs Bosch electronic units?