I have been working on the engine of my car for a couple of years now and the only thing left to do is to get rid of some misfires that occures once the engine gets from cold to hot (after approx 5min after first ignition, in idle). I have just finished an compression test and a leak-down test and there seems like there is no issue with leakage. (Wohoo!) I have also readjusted the throttle potentiometer, synchronized the throttles and changed spark plugs from NGK BR7EFS to NGK BR7EF which should be correct for the -92 year model.
Since the misfires only happen when the engine gets hot, I am starting to think that my ignition amplifier needs some attention. Inside the amplifier, there is this GM ignition module and I would like to replace this since it is quite cheap. According to a previous reply by Dr. Gregory Andrachuk from aug. 2009, the correct GM part no. would be 10482820 or 19180771. I have googled for pictures of this module and can see that there is a slight difference between those ones and the one in my amplifier.
Picture of GM 10482820:
Picture of my module:
At one of the mounting holes of my module there is something that looks like a ground connection to something inside the module. This is not present on the other GM modules. Was there an update from 19180771 to something else or do I have the wrong kind of module?
The ground connection might not look the same but it certainly has to be there for the module to work - and yes the module relies on the bolt or rivet that goes through the mounting hole to ground it to the case.
I googled GM 10482820 and saw both images in the results.
Suppliers may use a stock photo and the item you receive may not look identical to the photo. I have a few spare GM 10482820 modules and they all look like the one in the hand.
If the misfire occurs early in the warm-up, but engine runs OK fully warmed up, Mattias - the fault is not the ign amplifier module…
The module is just an electronic switch, and inside they are virtually identical, external differences are rather immaterial. As Andy says, the module body must be grounded to work - ‘tab’ added may just be an extra ground ‘assurance’. I’m more surprised by the lack of heat sin features…
If the engine works OK after warm-up; the problem is most likely associated with fuelling changeovers during warm-up. Warming up the engine by idling is a very long process, 5 minutes idling doesn’t heat up the engine very much. You should check actual temps around sensors when the misfiring occurs, just to get a better temp picture.
Generally, fuelling switches from cold to hot gradually as does the effect of the AAV, but perceptible may occur during the slow idle warm-up as the various sensor are not in perfect sync with engine requirements…
Be aware that the expected driver behaviour is to start the engine, then drive off - which will quickly heat up the engine, reaching normal operating temps after some 5 minutes of driving. In this situation there should be no perceptible adverse engine reactions - if engine management systems works as it should…
Thank you for the reply Andy, now I can order a couple of modules without any doubts. Unfortunately it is hard to get a hand on those here in Sweden, I have to order through Ebay from either USA or Canada. Strange.
Frank, sorry for this misunderstanding. The misfires occurs AFTER the engine has been warmed up, after approx. 5min of driving. During the actual warm-up there is no misfires. I suspected that there were misfires even when the engine was cold and that the effect was not noticeable since the fueled mixed air did not explode in the exhaust manifold when the exhausts still were cold. Then this fault would have been caused by a leaking valve but since my leak-down test and compression test showed no such thing I believe that I can search for other faults…
Also; I have restored my AAV and it works without any problem.
My throttle potentiometer should have been set at 0.32V in idle but I noticed that it was set at 0.11V. This is now corrected but I have not started the engine after the change.
I will order a new ignition module and see what happens!
PM me if you can’t get one. These modules only found their way into a few European cars so aren’t as widely used as they were in the USA.
Critical step when you replace one is to use heatsink grease between the body of the GM module and the aluminium AB14 case. This helps to conduct heat away from the module.
Every GM module I’ve bought came with a little packet of heatsink grease, but you can buy easily online if you don’t have any. Computer stores stock it too.
Interesting from afar. The module is indeed, a GM product. Developed by Delco. Used in many GM vehicles as a component of it’s HEI. High energy ignition. To remind me of it’s component use, I visited Google. The Wikipedia article was detailed and informative.
The somewhat different HEI in my somewhat different car uses a
similar module. Mounted on a “hear sink” and is replaced using a heat transfer “grease”.
In essence, the module uses electronics to perform the function of earlier “point and condenser” ignition.
I’ve never tried it. but a means of testing one,. is a simple test lamo to see if indded it is “making and breaking” the distributor
circuit.
I have been working on the engine of my car for a couple of years now and the only thing left to do is to get rid of some misfires that occures once the engine gets from cold to hot (after approx 5min after first ignition, in idle). [/quote]
Out of curiosity as much as anything else could you describe the misfire for us? Do you hear it in the exhaust of just one cylinder bank or the other? Is it like one or two cylinders occasionally dropping out? Or general idle roughness? Or…?
[quote=“Cadjag1, post:7, topic:354483, full:true”]
In essence, the module uses electronics to perform the function of earlier “point and condenser” ignition. [/quote]
Exactly!
[quote]
I’ve never tried it. but a means of testing one,. is a simple test lamo to see if indded it is “making and breaking” the distributor
circuit. [/quote]
Right. And unless a full, outright failure has occurred the testing must be done while the symptom exists
The most common scenario with these modules is failure after absorbing quite a bit of heat…typically after an hour or so of driving. The ignition system shuts down, sometimes preceded by a couple moments of very rough bucking and misbehaving from the engine. After cooling down a bit…30 minutes or so…operation returns to normal. Until, that is, enough heat is once again absorbed.
Of course, and to emphasize the obvious, “most common scenario” is not the same as “only scenario”.
However, if a running problem can be isolated to specific cylinders consistently giving trouble then the module can probably be eliminated from the suspect list. It is well upstream in the ignition system. A fault with the module would cause a problem with all of the cylinders, equally randomly…if that makes any sense !
Gotta catch it in the failed mode and then test there.
A bit ago, I “think” I fixed a somewhat similar issue with my daughter’s V6 powered VW Passat. I could not catch it in a fail mode. But a OBD II scan indicated 5 of it’s 6 cylinders misfired at times!!
My attack was a full on. New spark plugs, wires and coil pack.
A bit tricky to make the install, I was super careful to get it right., I did. it fired immediately and sounded oh so much better. That part quite subjective, yet indicative.
Alas, or mebbe not, she traded it in… No longer trusting her “space ship”.
My first “real job”, decades ago, was working the parts counter at the local Oldsmobile dealership. The parts department was large and, in the sense of physical layout, a logistical nightmare. To save steps and time we kept a inventory of the fastest moving parts right at the sales counter itself rather than in the stockrooms.
The infamous HEI module was one of those parts. We’d always keep them close at hand. The original part number, 1875990, is forever etched into my memory. Years later the part number was changed to xxxx466 (I can’t remember the whole number) and later was changed a couple more times, as we know.
If your module is stamped “990” it’s either an original or was replaced many years ago when stock of the original part number still existed. In Mattias’ case I see “466”, suggesting the module has already been replaced.
A change in part number generally corresponds to a change in design and/or change in supplier. I think one of the part number changes in the GM module corresponds to eliminating the use of beryllium…but I’m a bit foggy on that at the moment.
**
To clarify further, Mattias - there is no misfire while driving, but noticeable while idling after warm-up…?
Any odds that the ignition module is perfectly innocent. It simply switches coil-to-ground on and off, and the ECU uses this to trigger the injectors, but is not involved in fuelling computations. If the module fails; symptoms are usually, as Doug implies, more dramatic than ‘some misfires’…
As he also says; detecting if the misfiring is on one bank or the other is part of the diagnostic process. The V12 is very forgiving to ‘single cylinder’ anomalies - the multitude of cylinders smooth out faults - so the character of misfiring is of interest.
There are the usually two avenues; fuel and ignition. Mixture leans out as engine warms up. An interesting factor is if there is any unevenness/misfiring while idling semiwarm. Ie, does it misfire while the mixture is ‘cold rich’ or is it only when fully warm and 'lean. If warm only; the engine may run too lean - which Jaguars don’t like. A plain ignition problem would be mainly unaffected by mixture…
Mixture is controlled by the ECU based on coolant temp, manifold vacuum and throttle position/movement. I’m unaware of throttle pot adjustments made by measuring current - but assume you have access to manuals describing this. I’m only familiar with procedures involving ohming - after due mechanical pot settings…
It may be worth while to measure CO to verify if fuelling is correct - and adjust the manifold vacuum sensor accordingly. I assume you have verified that there is manifold vacuum at this sensor…
As an aside; while the ECU feeds both banks identically - sensor pick-ups are taken from one bank, and the other bank has to take what is given. Have you verified that both banks are running at the same temp - the dash gauge only shows one bank. A further reason to check if misfiring is related to both or one bank…
AndyBlakey: Thank you for the offer. I will get back to you if I see a problem with the ones I´ve ordered already. There was absolutely no trace of heatsink grease under my old module but I will be sure to use some when I install a new one.
Doug: I think the easiest way to describe the misfire is to attach a video from a cold November day in 2014:
The misfires only took place on the left engine side and got noisier after a couple of minutes during warm-up, as you can hear from the video. The misfire then was just as obvious in idle as when the gas pedal was pushed down.
But if we rewind time to a year earlier, to September 2013, similar noise from misfires could be heard from the right engine side:
As you can hear the misfires was not as intense as in 2014, just as if there was only one cylinder that misfired compared to a couple of more cylinders in 2014.
I cannot find a solid reason for the misfires to alter banks from right to left but since 2014 the misfires occurs on the left engine side and still does. Something tells me that this could be the effect of throttle synchronization failure but since there is a large air balance tube rear of the two banks this kind of problem would not be unless the synchronization was set severely wrong, right? The throttles were carefully synchronized (by myself…) one of two times between 2013 and 2014, maybe this was the reason for the change in misfires but unfortunately I cannot tell for now.
Doug (again): It´s much appreciated to hear from your past work. Each time my friends ask me how I solve all the problems with my Daimler I say that I get help from experienced guys like you and I am not shy to tell them some of your background stories and explanations. Maybe sometimes just to impress on my friends and to build up interesting stories around my own car.
Are you sure that the three digits on the module corresponds to the last three numbers of the GM module part number? I did just receive a module from Ebay (Canada) described as a GM 1875990 / Delco D1906 and it was also labeled “466” on top, just as my old one.
Frank: Thank you as well for all your detailed replies. I read all of them a couple of times just to make sure I have not missed any of your valuable thoughts.
I think your reply regarding fuel mixture leads me in the right direction. I took the car for approval at the motor vehicle inspection last fall but it failed due to a couple of reasons: weak parking brake power (now fixed), low-beam set to high (now fixed), ABS fail light not turning off (now fixed after a couple of weeks of ABS modulator- / ABS sensor- / wheel bearing- / ABS relay restoration) and also: TOO HIGH OXYGEN LEVELS in exhausts (now working on to be fixed).
As you say; since the engine runs rich during warm-up and more lean after warm-up (when the misfires start) it becomes clear to me that I could approach the misfires as a lean mixture problem. The coolant temp sensor has been checked OK as well as manifold vacuum. And as mentioned earlier in this thread the throttle potentiometer was recently adjusted (to 0.32V at idle position and 4.5-5.0V fully open as described somewhere, even by Doug Dwyer if I am not mistaken) although I have not tried to start the car since. Maybe all the problems are gone once I start the car… For other sensor checking, I bought and downloaded a useful manual for the V12 that I would really like to recommend: “XJS engine performance – Publication S-58” from 1987. This manual explains functions and adjustments of the V12 in very simple words and makes Jaguar-life much easier.
No, I am not familiar with the manifold vacuum sensor that you mention but would be really interested to know where I can find and test this one. Is it inside the ECU or somewhere inside the engine compartment?
Bank temperatures, yes. For a while ago I measured engine bank temperatures (by temp-sensor mounted on each side of the engine block and also be reading temperatures on each exhaust manifolds) but I could not get anything out of it. Maybe I should try to make new readings…
I will get back to you all again once I have started the car again. Then I will know if some of my adjustments have made any difference or not.
**
You have to run the car to see if there is any change after what’s been done, Mattias - then comment as required…
The manifold vacuum sensor is by the ECU - it is an essential item fur fuelling, and adjustable for mixture as well. Used in conjunction with a gas analyser, the mixture is set using CO as a tracer - to somewhere between 1 and 2%. Oxygen levels are not used for adjustments - there should be no oxygen present in the exhaust.
However, oxygen may be present due to a misfire on one or more cylinders - but with separate exhaust for the banks; measurements can be done for each bank to clarify. As said; I’m not sure if manifold pressure sensing is done from one or the other bank, or both - but fuelling is plenum, identical for both banks. If both banks are running lean; adjusting mixture at the manifold pressure sensor is the first step.
But if only one bank is showing oxygen; it is probably a one bank misfire - are still absolutely sure that the ignition sequence is correct - crossed leads will allow free oxygen to the exhaust.
The ign amplifier serves both banks identically - it cannot cause a single bank problem…
Your vide won’t play - I haven’t got the ‘new tab’ option…
**
Sorry, Mattias, still no joy - might be finger trouble in the long string…
However, I doubt if listening will clarify anything - just ‘that’ it misfires, but not ‘why’. The procedures for fixing a misfire is the same in all cases - a process of elimination. But have you started the engine again…?
