About us
Our Car
Chassis & Suspension 1
Chassis & Suspension 2
Engine 1 - Mechanical
Engine 2 - Electrical
Engine 3 - Cooling
*Misc Tech
*Misc Tech 2
*Misc Tech 3
Apollo Tank
Differential (LSD)
*Alcon Brake Upgrade
*Hellier Performance
*1.6k Repair
*1.8 Engine Upgrade
*Freestyle Motorsports
*Rolling Road 1
Rolling Road 2
Bullet Cam
Seven Re-build
L7C Dunsfold Slalom Day
Contact Us

See, now you would think that a Caterham 7 is one of the more simple cars on the road today, but here we see Peter C plugged into Mark's Vx 7 with a LAPTOP!!!

In my opinion electrical problems are the most frustrating problems to have. If a spigot has broken or a grommet seized, I can see it and understand it. It seems that any electrical problem I have had 'could have been a number of things' - or even more frustratingly - has been 'intermittent'!! ggrrrrrr

I shall try and explain a few issues we have had with our car - forgive the laymans terms - I am not an electrician. These problems/issues/solutions may well be unique to our car, but this is all from real experiences! If anything here saves you 2 days of hunting for that dodgy earth or loose connection by narrowing down your search, then it will have been worth it!!

For a period of about 6 months we had an occasional missfire from our engine. Nothing drastic, just a quick cough. The single miss seemed to be more apparent under acceleration at higher revs. First acceleration away from the drive would also produce a cough or two. As the weeks progressed this miss did seem to start to get more common.

The problem was that this 'missing' could actually be as a result of more than one fault, which made diagnosis harder. Earlier investigation had shown that when the engine missed, a click could be heard from the MFRU (Multi Function Relay Unit) - a relay tripping perhaps? This was hard to qualify simply because the miss was so intermittent.

Swapping an MFU box from Mark's old SLR seemed to fix the clicking, so I bought a new MFU and fitted it. Previously we had taken our old MFU apart to find a slightly dirty interior (seal had gone) and obvious pitting on some of the relays, which we cleaned up. This seemed to help, and we thought the problem had been solved.

However the single miss/click soon made itself apparent again. I took to carrying both new and old MFU's around in the car, indeed our hectic blast round France in the summer was all with the old MFU connected. Was a dodgy MFU a red herring or one of a number of problems? I don't know but the old one was pitted, so a new one may have eliminated one potential problem. There are pictures of the MFU at the bottom of this page, for your interest.

After changing this inlet manifold gasket the car would not start...

After the work on the inlet manifold gasket (which is detailed in the Cooling section elsewhere) had been completed I re-assembled the manifold and went to start the car. Nothing. The car did not even fire. Eventually it fired a little in a very lumpy way, but was certainly not going to start.

Logically it was due to something I had changed or moved. I checked all the connections and hoses to the inlet manifold, in case I had not reconnected something - all looked OK. Eventually after a lot of turning over, I managed to get the car started, but it had a very rough idle and the MFU was clicking away as the engine missed and eventually stopped. The frustrating thing was that the engine had been running fine 1 hour previously until I touched it! It was time to call in Peter C!

Peter suspected an earth problem - one of the first things he suggests checking in these situations. We looked at ours, and established that the local earth for the ECU was perhaps not brilliant. It was screwed directly into the aluminum scuttle, which had become oxidized and a bit dirty. We moved it directly to the negative battery terminal. Another possible problem fixed, but the engine still would not start, or if it did would hardly run. This was going to be a process of elimination! Next on the list was the IAVC.

IAVC - Idle Air Control Valve. This little valve sits on top of the plastic Rover manifold, and is used to regulate air into the engine when it is idling. Its really a relic from when the engine was used in a normal Rover. If for example the air conditioning is turned on when the car is idling, the engine needs a few more revs to power it. The IAVC opens a little and allows air into the engine, by-passing the throttle valve.

IACV - Idle Air Control valve -mounted on the k-series inlet manifold.

The valve consists of a stepper motor which winds a shaft in and out (controlled by the ECU) to block/unblock and air inlet that bypasses the throttle valve. These can become dirty/old and stick, thus allowing too much air into the engine and making starting difficult. It seemed that our engine was getting too much air when trying to start. Peter could get the car started by blocking the bypass air inlet a little bit with his finger, whilst simultaneously fiddling with the throttle valve! Engine would very lumpily start and idle, but without this fiddling it simply would not start. We spent a lot of time with this area. Taking the valve off we gave it a clean and a bit of WD40. We tried unplugging it once the engine had started, and although the engine would start this way, it still missed and ran erratically.

Again, the IAVC may have been a contributing factor to our problems, or another red herring, but it was good practice to check and clean it.

Throughout this exercise we had been re-setting both the ECU and immobilizer many times, as this seemed to help - something may have been causing the ECU to reset itself - perhaps a dodgy earth or power supply?

At one point the car was sitting idling away lumpily and I was fiddling around with wires under the inlet manifold. I touched the low tension wires on the coil and the engine stopped instantly. Umm...we checked these small wires and found the connectors to be very dirty and corroded - could this be the cause of our problem? Ironically these wires being corroded and having bad connections had caused us to become stranded at the side of the road on the very first day of owning the car. These wires shorting/sparking and generally not working correctly can also confuse the ECU - which could lead to other problems. At the time Caterham swapped our ECU and immobilizer entirely just in case. A little problem here had caused bigger ones. These wires are pretty exposed to the elements and worth checking.

Low tension wires mounted to the coil. Taking this plastic connector apart revealed corroded contacts. Incidently, you can also see signs of the coolant leakage above, where it had leaked from the inlet manifold and run along the head/block split line - details of this particular problem can be found in the 'Cooling' section.

We cleaned the low tension wire connectors up, and it seemed to help - the car started OK, and idled OK, but still missed occasionally. I carried on fiddling with wires. I touched the HT lead, and again the car stopped. This was very repeatable. With the car running if I pulled the HT lead very gently the engine missed, stuttered and then died, unless I let go in which case it would recover. BINGO!!

Hooking a finger around the high tension lead and pulling gently caused the engine to cough, splutter and stop. (This picture would provide a clue for the final solution - see later!)

I borrowed a coil and HT lead from Mark Collins and swapped them for mine. Car started first time, perfect idle and no missing.

High Tension lead attached to the coil. Pulling gently on this lead caused the engine to run lumpily, stutter and eventually stop. Pulling on the lead caused the lead to pull the coil connector in the direction of the arrow. I think it may be the internal connection with in the coil that is the problem, as I could not replicate this affect with Marks coil and my HT lead.

Putting my leads and coil back together again, the car worked. I suspected an internal connection in the coil (which is sealed) as a slight pressure on the HT lead seemed to cause the engine to miss. The connector out of the coil is male, and about 3 inches long - I think the engine misses when pressure is put on this. To be sure I replaced the coil and HT lead.

Early test drives revealed that the missing of the last 6 months had gone. The car felt much sharper - though this is not surprising considering it has probably been running on 3 and half cylinders with the coolant leak for quite some time.

So - in conclusion - it seemed that all our problems over the last 6 months could all be down to a dodgy/dirty connection to the coil. It COULD be that the MFU and IAVC issues were red herrings, or they could have been related. Certainly it has been good engineering practice to check and clean these components, but the coil problem was very repeatable (I have a very small video clip which shows this in action if you are interested) and all symptoms seemed to have gone now it has been looked at. Removing the inlet manifold obviously disturbed some already faulty connections and caused the car to not start at all.

I cannot remember how I actually discovered this, but here was the problem. The crank sensor is plugged into the engine block below the air filter. Its metal tip sticks into the flywheel, where it reads slots in the flywheel rim as the flywheel turns. The crank sensor tells the ECU exactly where the crank is, so obviously this is vital for smooth running.

Now it seems that this crank sensor and the signals it sends is a sensitive beast. Consequently the cable is shielded from other electrical interference with a sleeve - the textured black section shown in the picture below.

Red line circles the shielded section of the crank sensor lead. You can just see the actual wires coming out of the shielded sleeve under my thumb. The yellow circle shows the HT lead clip.

Now, it just so happens that the HT lead which runs from the coil to the distributer, and obviously carries strong impulses of electricity to produce the spark at the spark plugs, passes pretty close to where the crank sensor lead also joins the main loom. The HT lead is SUPPOSED to be clipped up away from the crank sensor lead by the clip, shown in these pictures with a yellow circle, which is fixed just below the throttle body on the Rover plenum.

Small plastic clip which should hold the HT lead away from other cables, such as the crank sensor lead. My HT lead was not in this clip, and so had dropped too close to the crank sensor wires.

Now my HT lead may well have been unclipped for a while, but one thing is for sure, when I removed the inlet manifold to fix the gasket, I certainly did un-clip the HT lead. In fiddling with all the cables and wires, I must have pushed these two cables together, which is why we could not start the car. The strong signal from the HT lead was confusing the signal from the crank sensor, and the ECU could not get a clear signal telling it where the engine cycle was. The ECU relies on the signal from the crank sensor to operate the fuel pump (amongst other things) so if this was corrupted it would explain why the the fuel pump in the MFU was clicking away.

Another clue can be seen in the picture below. This was supposed to be showing me pulling the HT lead and causing the engine to stop - I thought it was because the HT lead had a bad connection to the coil, but what it actually shows is me pulling the HT lead even closer to the crank sensor cable, which would cause the engine to stop altogether.

Photo shown earlier - green line shows the HT lead, red shows the crank sensor cable - you can clearly see the HT lead is not in the clip it should be, and that the 2 cables are pretty close.

This problem is easily and 100% repeatable. Un-clip the HT lead, bring the two cables together, and the engine stops.

So - the solution was easy. I clipped the HT lead into the clip, having first re-routed it as far away as possible from the crank sensor lead. I then re-routed the crank sensor lead in the same way. I also re-positioned the shielding shroud on the crank sensor cable, which is really a bit too short and was not in an ideal position.

Needless to say, the car has not missed a single beat since - phew!

See - we got there in the end! If nothing else it has shown that you need to look at everything, check every cable, every connection and every possibility! Check earths - there are more than one. If something goes wrong or stops working, think about if anything has changed - what did you touch or move. In our case our missing problem was exasperated by me when I was replacing the inlet manifold gasket, when I inadvertently moved and unclipped all the cables below. Our missing problem COULD have been caused by any of the other issues listed on this page, so all are worth knowing about, but I am confident that the main cause was the interference between the HT lead and the crank sensor cable, and that it is now all fixed. I'll keep you posted!

The MFU contain fuel pump, starter, lambda and main relays on MY car, which is a '95 1.6 k series. Later ones may be different. When I say 'OLD' MFU I mean mine. 'NEW' refers to the later MFU's found on newer engines. The 'new' one illustrated here is from Miraz's 1.8 SV engine.

My MFU is on the right. A later model is on the left. The physical difference is highlighted as an easy way of identifying the different models.

My engine is a '95 1.6k - a pretty early model.The later MFU does not work on my engine.

Showing the part number for a later MFU, as found on Geoff's SV. Attaching this to my car resulted in a load buzzing from within the MFU.

Only part number on mine is inside on the circuit board!

MFU pulls apart. It should be sealed with a gasket - mine was not, suggesting it had been taken apart in the past.

The four relays. Clockwise from top left: Fuel Pump, Main, Starter, lambda.

The highlighted area shows the contacts that had visible pitting on our MFU - this was cleaned with a small piece of emery paper.