After four years of "trouble free" performance, the cat left me stranded at a stoplight the other day. It was running fine, but died while waiting for the light to turn green.

Anyway, it's back home now. Breaking open The Book, it didn't take long to isolate the potential problem as the ignition control module. A quick trip to the auto parts store and I've now got it running. It took some coaxing and no small amount of backfiring before it ran smooth. I let it warm up and...feeling apparently more proud of myself than the cat felt justified...I took it for a test drive.

As long as I didn't want to go over 15 MPH it worked great. Anytime I'd try and give it more than idle throttle, the engine would "surge"...the RPM would jump up and down from 500 RPM to 1500 RPM. I've never had that happen before.

I'd noticed in the past that when at idle it would infrequently do something similar. The RPM would just drop for maybe 1 to 2 seconds. It would never die, but would recover. I never noticed this behavior when driving it.

Palm mentions that one has to "keep trying" in order to get an ignition module that is reliable. But does this new problem...not being able to give it any throttle...sound like something a funky ignition module would cause? Something tells me it's a fuel flow issue, but the coincidence is very difficult to believe.

Thanks,

John
1987 XJ-S V12
65,000 miles

 

sounds like fuel to me, check out the fuel pump, filter, and regulator. I have had 2 pumps die, so fuel issues seem like a typical problem to me, and they act just like cars do when running out of gas, running but not allowing revs and having the idle jump about a bit, its worth checking out.

 

Did you replace both coils?

 

I have had module duds down here.

I use Echlin brand for a very long time, but not available here anymore, and they were fine, always.

The Tridon brand last week appears OK, as of typing this.

The coil/s could be iffy now, as that module controls coil voltage (among other things). Run it for a few minutes, shut it down, feel the coil, noting if it "feels" hotter than the surroundings. Warmer would be "normal", but hotter indicates either a coil or a dud module.

You guys up there have access to the GM brand, I think, we dont.

Lift the distributor cap (I know its a fun job), turn it over, ensure the carbon contact brush is still there, and not burned away. That is one I have seen/experienced a number of times, and it gives the EXACT symptoms you mention.

 

Got a chance to inspect "the dizzy". No evident damage that I can see. The shiny spot where the carbon contact touches looks clean. The edge is a bit ragged in my less-than-perfectly-focused photo, and the carbon contact inside the cap looks good.

So....tomorrow it's back to the parts store to get another ignition module (lifetime warranty, so no cost), and I suppose it's time to replace the coils anyway since they look original. If that doesn't fix it, time to look at the fuel flow.

I did away with the supply fuel regulator a few years ago. If the filter and pump are ok, I guess I'll need to replace it which, given its cost, I hate to do if it's not the problem.

Is there a way to test this regulator?

Thanks,

 

That cap and rotor look just fine.

The RH FPR removal is a permanent fix. It is not needed, full stop.

The fuel filter, and the one in the sump tank are #1 on my list, then the pump, IF that module is deemed OK.

 

Our weather hasn't improved enough for me see of the solution to my problem lies with the fuel filter, pump or sump, but I did get a bit of time today to try something else.

Not being a huge believer in coincidences (why would I suddenly have a fuel delivery problem at the exact time my ignition control module went out) I picked up another control module today and put it in. No joy...still idles great but cant get any power out of it.

I did take a video that illustrates the problem better than my words. Please note that my hand is steady on the throttle turntable...something else is "revving" the engine.

For a quick experiment, I pinched the vacuum line running to the return fuel regulator. I then took the vacuum line completely off the regulator. Nothing changed.

Any new thoughts?

Thanks!

John
1987 XJ-S V12

 

Weather and time finally allowed me some bonding time with the cat. Sadly, problem remains.

What I did this weekend...

New fuel pump.

New fuel filter.

Removed and cleaned out fuel sump. My car has the late model larger filter screen. Cleaned it.

Rewired the fuel pump ground connection. Checked voltage at the pump terminals, getting over 13 volts at idle.

So...what am I down to??? Fuel outlet regulator, coils? I took my inlet regulator off a year or so ago, so that's no longer a factor.

A clue that may mean more to you experienced types. Back when it ran properly, it could be a bit difficult to start when it was "cold", but since this problem has cropped up starting it cold is a 5 minute ordeal (and by "cold" I mean 40 or 50 degrees F). It cranks fine, but goes though no small amount of hesitating and a bit of backfiring before it will start. After letting it warm up a bit, I can shut it down and it'll fire up just fine.

Short of replacing it, is there a way to test the outlet regulator?

So to summarize, very difficult to start when cold, easy when warmed up. Idle is great, but anything above idle power quickly drops out. Pretty much everything fuel related in the boot is either new or cleaned out. Problem began after replacing ignition control module.

Thanks,

John
1987 XJ-S V12

 

OK, fresh bottle opened, so here goes what I have had over the years.

Your list of items is good and assists greatly.

The cold starting is odd, as they usually fire right up, and the hot side is the issue.

Have you checked the TPS?. It is old now, and they are a mongrel and do cause the fluctuating revs you are seeing, AND, the cold start, and the lack of oomph.

Using a DCM (digital volt meter) probe the TPS at the 3 pin connector. I forget teh 2 colours now, but itis easily found, Red and Green I THINK??. Set teh DCM to the lowest DC Volts, usually 5V, and turn ON the ignition. You should see 0.32 - 0.36V at idle. I have a Word doco on this if you want it.

If its too low the fuel circuits of the ECU are confuded at best. If its too high, the ECU will overfuel the engine.

If you got that V reading, then slowly OPEN the throttle, and watch teh readings rise SMOOTHLY to about 5V at full throttle. If there is ANY fluctuation of the readings whilst doing this, the TPS is highly suspect.

Another quicky. Ign ON, rotate the throttle capstan QUICKLY, and LISTEN. You should hear the injectors "fire". If so, the TPS is talking to the ECU. If no "fire" then the TPS is again suspect.

Another, I am boring. The Resistor Pack, mounted inside the engine bay, hehind the RH headlamp, is also causing grief of late. Greg in France has done a TOP write up of this and its effects, and the FIX, and I think its in the "stickies" at the top of this section.

The sychronising of the throttle crossrods is also critical for smooth "off idle" rev rise. If they are out of sync, the 2 engines will fight each other until about 1200RPM.

 

The "new" ignition modules available today are pretty much crap IMHO. The NOS ones have a specific grounding "Lug" where the one mount screw gores through that is missing on the new ones, even the newer "echlin" ones from NAPA. My car will not run on one of the new ones, I found an NOS GM one on eBay and my car runs/starts fine now. I went through three newer ones with no luck. Remember theses things are designed to fit in a GM HEI distributor where the newer design may not be an issue with the grounding lug.

 

Here's a proper NOS one. http://pages.ebay.com/link/?nav=item...d=231425978488

 

Thanks for that.

The latest update isn't so good...new ignition module (the "new" style), new fuel outlet regulator, and new coil, the single DAC6093 that Jag recommends. No change in engine performance.

I've not yet tried Grant's suggestion on the TPS, will do that tomorrow.

Just went to the link you provided and bought two of what hopefully will be the NOS ones, at least that's what the picture shows.

Oh, just for laughs, I did try running a grounding strap from the mounting hole that, in the NOS versions, has the bolt. Ran it to the manifold right under the ignition module housing. Didn't make any difference.

Just curious, when you say that yours will not run on a new one, do you mean it won't start at all? Just curious how it behaved.

Grant, I can hear the injectors fire.

Thanks,

John
1987 XJ-S V12

 

It would not even start, literally in minuets I'd put the old in and it'd fire right up, go down to a different parts store, get a different brand, no joy, old one back in fire right up. I went through a wells, standard and echlin. I'm up against similar problem with what I hope is coil/amp, also ordered one from the link that shipped today.

 

Just had a thought.

I get these flashes from time to time. Old age and JD does that.

Inside the ign AMP, and tucked in one corner, held down with a small screw, is a "capacitor/condensor" that is plugged into the module on 1 of the +ve spades. These things leak to earth, and I remove them ALWAYS.

I have never had an issue with the Zenor diode imbedded in the casing, although some have. If it is in doubt, unplug it, and see what happens. Dont leave it unpugged, as it is a protection item for the system in the event a spark plug fails to fire and feedback from the coil spikes the module.

 

Grant
Here is a photo of the inside of the amp. Could you please identify A, B and C for me, so I am sure what I can remove and what not?



(an "Orangeblossom system" edited photo)

Greg

 

Greg.

It is C that is removed.

Long time since I seen inside one of them. Soooo reliable with that C removed.

A is the Zenor diode.

B is the "blob" containing 2 resistors. One is for the tacho drive, the other is for the "shielded wire" to the ECU. I have never had issues with the blob, but some have.

 

The zener diode is in the upper right of your photo (A).

"C" is the capacitor or condenser depending on your preference of terms.

There are some resistors buried in "B".

I'm going to play with these this morning and see what results I get.

Thanks,
John
1987 XJ-S V12

 

In my case, removing both the capacitor and/or the zener diode had no effect. I've put the zener back in.

I did test the resistors in the blob, both are ok.

Wondering...if there is a vent line blocked somewhere (sump???) would it show similar symptoms?

Thanks,
John
1987 XJ-S V12

 

Another days experimenting over, with no new results.

I did pull the two front spark plugs to see if they might reveal any clues, but as far as my limited experience can tell they look normal.

As mentioned above, I disconnected the capacitor and zener diode in the ignition module. No difference.

The fuel tank had only about three gallons in it, so just to try something different I drained that and put in about three gallons of super unleaded. I went though the five minute starting process, got it running, and let it idle for about 20 minutes just to see if water or fuel contamination might have been the problem. No change.

Oh...when it finally "starts", it can only be running on one or two cylinders. If you've ever heard a airplane radial engine start after it's been hand cranked you get something of the idea, except that instead of all the cylinders lighting pretty quickly it will take it several minutes until all the cylinders are running. During this process, if I put any pressure on the gas pedal at all, the RPM (which is around 400 or so) will drop and it sounds like it's going to die. When I get off the pedal it goes back to chugging away. Eventually it gets up to 1000 RPM and sounds smooth. But opening the throttle results in power loss.

If I shut it off and crank it again after a few minutes, it starts right up. But still can't get any power out of it.

Thanks,

John
1987 XJ-S V12

 

Being Sunday here, and BBQ is heating up, I will touch on some suggestions. Ignore whatever you have covered.

Is the spark a FAT BLUE CRACK of a spark, or a weak as water yellow affair. The HE requires the former. The coil/s are the prime culprit here. Teh actual engine straps are 2nd culprits. They must be 100%+, and I always run a dedicated engine to chassis earth cable whenever I am under one of these beasts. Even my 2 X200 S Types now have MORE earth straps, engine to chassis, and the mystery mis-fires in the Black Beast have GONE.

Disconnect the fuel inlet hose at the rail. Insert said end (extended as needed) into a container OUTSIDE the engine bay, and turn ON the ignition. DO you get a GOOD flow of fuel into that container during the "prime cycle"?.

Have a GOOD look at the fuel return line running under the LH side of the car on its way back to the tank. This pipe is easily damaged, as in crushed, and that prevents fuel returning to the tank, and the Domino effect is that the fuel rail over-pressurises, and the engine over-fuels, and "chugs", "lacks power". The HE hates too much fuel, unlike its sister, the PreHE which has a real love affair with fuel.

Some markets, and I have NO idea what your market has, have a fuel valve/reducer JUST INSIDE THE ENGINE BAY on the RH side, where the metal fuel pipe enters the engine bay, where our RHD brake booster is located. This is well documented as a problem item. My '85 had one. I removed it, and fitted a suitable EFI reducer (10mm to 8mm) and some of that cars running issues vanished.

The rubber grommet at the front of the distributor has the 2 wires passing thru it for the amp. These wires have a habit of breaking INSIDE that grommet. My '87 drove me nuts with that one.

The actual reluctor inside the distributor have been known to go AWOL, but I have never had that happen. That would give a definate flaky signal to the module, so spark would be a hit and miss affair.

BBQ is ready, back later.