Lads:

Still working on my TR7 breaking up above 3500 RPM. I had previously mentioned that I have replaced the plugs, wires, rotor and cap in the ignition system. I have also gone through the carbs in great detail - diaphragms are good and the plugs are pale tan color, indicating the mixture is lean as expected. Ignition timing is spot on, and the mechanical advance is working well. I did a crude back pressure test on the exhaust system, where I hooked up my compression gauge to the air injection rail (air pump disconnected) and measured 0. I am sure it is not zero, but the markings are close together so it was less than would register. I may try again with my vacuum gauge which is much more sensitive, since it measures pressure as well as vacuum.

The engine starts to sputter above 3500 RPM, but if I accelerate gently enough I can delay the onset of the breakup to about 4000 RPM or so. The car starts and idles perfectly, and has decent power below that RPM.

Here is my question: The ignition system is the stock French Delco system - all original. High RPM break up is sometimes a symptom of a coil failure. I don't have a coil to swap in, so I am looking for some good information on diagnosing the Delco system. Anyone have any good links or other references to troubleshooting the Delco system? If it is the ignition, it seems that it must be the coil or the control module.

At one point I thought perhaps the dampers were incorrect on the carbs, but they are the correct dampers, and I have changed the oil so that the dampers are moving up and down freely, although a bit stiffer than I expect. The air valves do not hang, open fully, and the needles are in the center of their travel.

Please post any good links or references I can use to bone up on the Delco system.

Thanks,

Vance

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1980 Platinum Metallic TR8, frame off restoration, complete.
1980 Vermilion TR7 Sprint replica, in progress.

Hi Vance,

Does it break up above 3500-4000 only when under load, or does it even when sitting in the driveway? Have you done an ignition cut when it breaks up, and try to read the plugs then? Have you checked fuel pressure/flow when it starts to break up?

Sorry, can't help with the ignition question, though.

-Darrell

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Darrell Walker
66 TR4A IRS-SC CTC67956L
81 TR8 SATPZ458XBA406206
Vancouver, WA, USA

The best I have been able to find is for the US version of the Delco HEI. The US version mounts the amplifier in the distributor, and the coil on the distributor cap. The TR7 version mounts the coil and amplifier remotely, on the left inner fender.

Here are the best links I have found: Hemmings HEI troubleshooting and Autozone HEI diagnostics.

I like the second one because it gives the specs on what you should measure, but I cannot be sure that the TR7 unit will measure the same, and the wiring is completely different so the diagram showing where to test are useless.

OK, so if I ASSUME that the guts are the same, but the physical layout is the only difference, then I have found a major problem.

Autozone says the pickup resistance should be between 650 and 850 ohms. Mine measures 777 ohms, There should be an open circuit between the pickup and ground, and indeed mine is open circuit. They also specify that you should operate the vacuum capsule while taking the measurement, to make sure the pickup connection is not intermittent. I did this, and found no issues.

Next, you should measure the primary side of the coil - this would be the spade connectors on the bottom edge of the coil. There are two pairs of spade lugs, each pair is shorted together, and each pair connects to one end of the primary (I think). One pair is labeled "+", and the other pair is labeled "-". The Autozone article says I should measure less than 1 ohm primary resistance. I measure 0.85 ohms between those two terminal pairs. Spot on.

OK, the secondary resistance between the high voltage tower and the "-" terminal (ground) should measure 6,000 to 30,000 ohms. This is where things get fuzzy for me. The directions say that you should measure between the HV tower and the tach terminal. There is no tach terminal on the dizzy, but the tach signal would be pulled off the "+" primary terminal, correct? So I measure an open circuit, which on my meter means that the resistance is greater than 30 Meg Ohms (30,000,000 ohms). Autozone says not to replace the coil unless both primary and secondary readings show open. It does not matter which primary terminal (+ or -) I use, I get an open circuit on the secondary.

This does not make sense to me (Like Buddhism and politics, which don't make any sense either). If either primary or secondary show an open circuit, the coil is bad, yes?. Why would they say that both the primary and secondary need to be open? Perhaps it has to do with the circuit differences between the GM HEI and the French unit?

It seems possible that what they mean is that you should take two readings on the secondary, one to the + terminal and one to the - terminal, and both of those secondary coil readings must be open, instead of both the primary and secondary measurements must be open. But a careful reading of the instructions say that both the primary and secondary readings must be open. Hmmm.

OK, if it is indeed the coil, this looks like a replacement coil: ENA UF-88 coil for Renault. The primary terminals are arranged slightly differently, but that is trivial to deal with. The Delco D525 us also a replacement, but it requires a different High voltage lead to the dizzy.

Anyone tried the Renault coil? It is a bit pricey, but if it is a drop in....

Vance

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1980 Platinum Metallic TR8, frame off restoration, complete.
1980 Vermilion TR7 Sprint replica, in progress.



Edited 1 time(s). Last edit at 2019-01-08 07:37 PM by Darth V8R.

Wedge-heads:

I just took the Great Pumpkin for a spin after replacing the original coil with the Delco D525 coil. The Delco D525 coil was too cheap to pass up, $18 and free shipping.

I had to modify the high voltage lead to the coil to get everything to fit. I removed the existing boot, crimped the ferrule a bit tighter to grip the male terminal on the coil, and added five layers of heat shrink to insulate it.

My high RPM break up issue is totally resolved. So it was the coil, even though the car would start and idle just fine, it would sputter and refuse to rev much higher than about 3,500 RPM.

I have attached a photo of the coil assembly (painted, and the new coil in place) for your amusement.

Cheers,

Vance

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1980 Platinum Metallic TR8, frame off restoration, complete.
1980 Vermilion TR7 Sprint replica, in progress.

Xlnt. news.
It's my experience that the 1980-81 Delco distributor/coil combo is as bulletproof as you can get.

My '79 Coupe came today, but I didn't check to see what dizzy it has.
If it isn't the Delco, it soon will be.

Vance,

The end result looks fantastic. For the non-expert/Concours judge, it looks original. Well done! Yes, these Delco coils are typically reliable, but it is now great to see that both electrical components can be soured fairly easily if they do fail. I think TWOA would be happy to have an article written up to publish on that TR7 coil.....

Vance, great research and application on using that coil. Should save yourself a lot of time when looking for a replacement.

In looking over the directions for mounting the module you posted it says to use silicone lubricant, I'm pretty sure it should be "White Thermal Grease Silicone Compound Paste", that is quite different from a silicon lubricant. There's other thermal greases that are not silicone.

So, at best, those instructions seem a little daff.



Edited 1 time(s). Last edit at 2019-01-13 10:26 AM by Mr. Nuts.

Vance,

Congrats on successfully diagnosing and fixing the problem, now that it's running great you can tear it down to the bare block to start your Sprint project. Any reason you didn't just skip the last step and go right to the tear down?

Dave:

I did indeed submit a write up to Jim Tencate, along with some photos and part numbers should one need to replace the pickup coil or the amplifier module. I just sent it in yesterday, so I have not heard back if he wishes to accept it.

The coil is listed as a substitute on this web page, so I did not come up with that one but I did track down the UF-88 as a replacement which requires fewer modifications to install.

Vance

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1980 Platinum Metallic TR8, frame off restoration, complete.
1980 Vermilion TR7 Sprint replica, in progress.

Kevin:

They are more than a little daft, aren't they? Yes, it should be heat sink compound, not silicone lubricant. The instructions also claim that both the primary and secondary must be open before the coil can be considered bad, which I whined about in a previous post.

There were a couple more pages to the write up that were equally jumbled. I like their write up though, because it gave actual measurement values to determine the pass/fail state of the components, something the Hemmings article lacked. Best I can tell, their test limits are correct for the TR7. The illustrations are useless though, because of the physical differences.

Well, it all worked out in the end, and the engine is running well. Took it on a brief five mile jaunt today to see what else needs attention.

Here are some of the issues I spotted today; squealing brakes, sticking tach, notchy shifts...

Cheers,

Vance

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1980 Platinum Metallic TR8, frame off restoration, complete.
1980 Vermilion TR7 Sprint replica, in progress.

I'm just wondering if the idle speed has become a back shelf issue but great work on the ignition. Did you ascertain where the failure was in the coil ? As other's have mentioned they are considered 100% bulletproof. Basically unheard of any failing. Until now, presumably.

Idle speed was solved by oiling the throttle linkage. The butterflies were not returning to the fully home position. Details matter, as we all have learned personally.

All I can say for certain was that the coil secondary measured over 30 million ohms, and the spec is 6,500 to 30,000. My guess is that there was an open and the high voltage was able to jump whatever gap there was, at the expense of greatly reduced secondary output voltage. Enough to fire the plug at low engine speeds, but not enough to deal with the increased demands of higher RPMs.

Vance

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1980 Platinum Metallic TR8, frame off restoration, complete.
1980 Vermilion TR7 Sprint replica, in progress.

Here in Canada the Delco system has a very bad reputation and nearly all have been swapped out

I did have misfiring at high rpm.

Threw the delco away . Istallled crane cams flame thrower set up
No more problems at all

I am curious what parts of Canada have determined the TR7 Delco ignition to be poor quality. Out here in the east, it is the earlier "hopeless" OPUS that fail at a high rate. The 1980 onward TR7's with Delco ignition are reliable around here. Maybe it's that Pacific Ocean effect?