45 Second Timer

(Robert King) #1

On my ‘88 5.3L, the 45 second timer has apparently died. When I was diagnosing I found that the connector pin out does not match the circuit shown in the V12 Focus Manual. Wire colors and function match; however the wires are not in the correct number cavities. As the connector does not appear to have been tampered with, and I can actuate the SAV and vacuum solenoid by grounding the pink/white wire, I am ordering a replacement timer.
I also checked the Electrical Data chart that came with the car, but cannot locate either the timer (not indicated in the legend or schematic) or the SAV (which is called out in the legend).
Incidentally the symptom is a low idle for the first 30-45 seconds- only if parked overnight. After first start of the day, idle is fine with subsequent starts. I recently have rebuilt the AAV and checked out it’s calibration, so that is not the issue.

(Doug Dwyer) #2

I’m not exactly sure which data chart you are referring to. Both my V12 Jags had/have wiring diagrams in the owners manuals. Is that what you mean?

If so, I suspect that not every possible market-specific build configuration is included


(Robert King) #3

Yes, that is what I am referring to, genuine Jaguar document that is the size of the owner’s manual when folded.

(baxtor) #4

If you search “jaguar xjs 1981- 1988 engine performance PDF” you should find the timer shown in schematics at the tail end of that document. Not sure if it is what you are looking for.
There seem to be quite a few discrepancies in the jaguar wiring diagrams.

(John) #5

This sounds strange… actually if your timer is not working or it is disconnected, your idle should be fine as you should get vacuum advance from the start. What timer does it disables vacuum advance for first 45sec. after startup ( no matter if it’s cold or hot) and activates supplementary air valve because retarded timing will cause idle to drop. If you experiance low idle at startup I would guess that your vacuum switch (that disables vacuum abdvance) is working, but supplementary air valve doesn’t, so you get low idle for 45sec. after startup. Although it should be the same no matter if it is hot or cold. Also if your car doesn’t have cats anymore you can just disconnect the timer and forget about it.

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(John) #6

I would start by checking vacuum lines if they are connected as according the scheme (there should be a sticker under the bonnet) The only thing that comes to my mind that operates only when engine is below 45c is vacuum valve for air injection system, but that shouldn’t cause idle drop unless someone was messing with vacuum lines and somehow connected them wrong.

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(Robert King) #7

The document you refer to is the same document with a different title. Just a discrepancy in the cavity numbers I will assume.

I did find the timer available new from Martin Robby; about $15 US- probably the least costly part on this car!

(Robert King) #8

I have verified that the air pump diverter valve is working; it is controlled by coolant temp only and is functional longer than 45 seconds from cold. I can ground the pink/white at the timer and the idle will increase, although I have not tried it from dead cold. Timer is on its way, as I have confirmed that it is not working and will see if it helps. Thanks to those who responded.

(Robert King) #9

I already thought of that and verified correct vacuum line connections, but you may be on to something- I wonder if the vacuum advance unit has failed. I will check it…

(Robert King) #10

Well the plot has thickened; vacuum advance is still good and working, bench- tested the 45 second timer and could not get it to work. Ordered and received new 45 second timer from Martin Robey and installed it, but the supplemental air solenoid and vac solenoid still are not working. Have not had a chance to bench-test the new one…but as been pointed out, with vacuum advance not blocked, shouldn’t need supplemental air.

Now that temps in the morning are 20 deg (F), engine starts easily but starts to load up almost immediately, and I have to hold at 2000 rpm for about 30 seconds, then it clears and idles fine. Subsequent starts during the day have no issue. Runs fine otherwise. Coolant temp sensor values seem correct.

Ideas anyone?

(Doug Dwyer) #11

Can we clarify ‘load up’? Is it actually loading up, that is, running too rich? Like a stuck choke on an old carburetor? Chugging, black smoke type of thing?

Or is is actually running poorly due to lack of mixture enrichment? With the extra RPM masking the condition?


(Doug Dwyer) #12


This may be of no interest to you…

I have a 1988 engine in my 1985 car. I have removed the AAV, the EAV, the 45 second timer, the idle control relays, and the regulator to the vacuum advance capsule.

The engine starts easily and idles perfectly when cold, even after sitting overnight and with ambient temps at freezing or below. Start engine, drop trans into gear, drive off.

I do, however, have the base idle set a bit higher the normal. The S58 performance/focus manual calls for 750-850 RPM, hot, in “P”. I have my base idle set to about 900.

On cold mornings I’ll pulse the injectors once for an extra-easy start. In freezing temps, I’ll give two pulses. Key ‘on’, jab the throttle smartly.


(Robert King) #13

Yes, by loading up I mean running rich, smoking at the exhaust, and rough. As I open the throttle to hold at 2000 it misfires, runs ragged, and then clears and starts firing on all cylinders. Funny thing is that when it is first started from overnight, with no throttle it starts and it runs smooth at about 1100 rpm for a few seconds before it starts to foul out the plugs.

(Robert King) #14

My hot idle is about 850. I did today check that the MAP sensor on the PCM does hold vacuum and that there is no condensation in the line from the intake manifold crossover to the PCM.

(Doug Dwyer) #15

For a few moments the cold engine likes the extra fuel, I reckon.

I wonder if you have some injectors leaking down overnight?

A poor connection at the coolant temp sensor could cause a problem even if the sensor itself is OK.

Excessive fuel pressure can cause over fueling…although I’m a bit hard pressed to imagine a pressure regulator giving a problem for only 30 seconds and only when the engine is cold.


(Scott Horner) #16

My car had a similar cold start issue. It would start on half a crank of the starter, but then be overfueled for the first 3 minutes, but not enough to stall out. Once the ECU detected some heat in the engine via the CTS (around 50 degrees C), it would reduce the amount of fueling. I replaced and tested the CTS both at the engine and in the trunk to validate whether or not I had an issue with it, or the wiring, to no result. I also tested my AAV and modified it to get more air when cold.

In the end, I fitted a 2K (I think) ohm resistor in parallel across the CTS signal, which makes the ECU think it’s warmer than it is on start-up. It also makes it think it’s warmer across the entire range, but this is an inverse scale, so while the difference at cold is around 20 degrees C and when hot is only around 3 degrees C.

This has made my car much easier to drive when cold and more economical all around. Although it does have to crank for about 2 seconds to start now.

I have an AJ6 Super Enhanced ECU fitted and I just figured my cold start calibration table must be out. fitting the resistor was easier than sending the ECU to England.

To figure out the resistor I needed - I used this website - https://www.allaboutcircuits.com/tools/parallel-resistance-calculator/ and then used the reference table from the Workshop Manual to determine the resistance at a given temperature.

Hope this helps.


(Robert King) #17

Thanks Doug and Scott, injectors might also account for the occasional rough idle when hot. Scott’s idea would be easy to try. Today it was near 50F; didn’t load up on start, but idle dropped from the initial 1100 to about 350 for the first minute, then steadied at 1000 until hot.

(Robert King) #18

Well, I have identified the issue, at least in part. I made up a short test harness that plugs between the EFI harness and the temperature sensor that has an additional plug that I can use to add a resistor in parallel with the sensor and measure the voltage that the ECU is seeing.
First I measured the coolant temp sensor resistance; it was 5660 ohms at 32 deg F- nearly exactly what the V12 Focus manual says. Then I checked the voltage with the key on; which was over 3.8v(should be 3.1v). The 3.8v would make the ECU think the engine was somewhere below 0F degrees, which in turn would cause the over fueling.
I calculated a 5000 ohm resistor in parallel would put the voltage at 3.1; closest I had was a 4.7K (which actually measured a tad over 4.8K). With this in the circuit, the voltage was just over 3.0V at 32 deg F, and the engine started and idled fine.
It appears that the ECU is at fault, as high resistance in the wiring would cause a lower voltage at the sensor. Anyone know if this sensor is supplied through the same 5V regulator on the ECU board as the TPS?
The other thing I noticed is the idle fuel pressure is 32 PSI at 17” of vacuum, and rises to 40 if the vacuum line is removed from the regulator, which seems about 3 PSI high, probably not helping. Could be my gauge…


Do I follow that you feel you are getting more than 5v to the CTS? Because you have correct resistance in the CTS, but more volts out than you have calculated 5v through 5660 ohms should be?

Should be 36 psi ( 2.5 bar ) without vacuum. Surely not helping.

Have you checked the setting of the ECU trim pot? Is it possible the PO has adjusted it?

(Robert King) #20

I guess that is the direction indicated; that the regulated 5V is too high. I have not checked the feed to the TPS, only the signal at idle.

There seemed to be insufficient range to adjust lean. It was at limit of adjustment and still above 2.0v, which indicates rich. Idle is pretty good though, with 16 to 17” vacuum and adjustment up or down with idle speed screw.

I also disabled purge and PCV; made no difference other than a 600 rpm idle.