Granted, this strategy might no be very scientific, however it deserve to sometimes bring you close.

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With this one I need to define a little an ext than usual around the car history. This automobile was a 1999 Ford Escort 4 cylinder 1.6 litre and also had to be bought by the new owner from a dependable used vehicle lot with no apparent problem whilst at the lot. After ~ a couple of weeks in the hands of the new owner, the auto had second inventory of lower springs, alloys, up-rated stereo, and two huge holes in the behind parcel shelf all set for some speakers. One morning the automobile owner involved start the car and also it cranked however wouldn’t fire.

The vehicle was went back to the sales lot whereby they invested some time on it yet had no luck. It then acquired referred come a local garage where they managed to build a bigger snapshot about the fault. They found the car had spark at all four plugs, all 4 injectors to be firing, fuel push was good, compressions to be good, and it had a secure gas flow through the tailpipe; it seemed to have actually everything. There to be a clue in that occasionally the engine would backfire together with a suddenly crank rotation lock-up; both indicative of one ignition timing issue. The garage traction the timing belt sheathe to inspect belt condition and mechanical time marks, but all seemed OK. They changed the CKP sensor, equipment a different CMP sensor and a different coil pack, and a new ECM was next on the list. The was here that ns got referred to as in.

The garage additionally queried even if it is the OEM PATS immobiliser was having any influence. Lock were certain of a spark existing at all plugs and the injectors were undoubtedly firing. This, coupled v the fact that the PATS MIL wasn’t flagging a fault, didn’t at this stage give any cause because that concern, for this reason I moved on come other an ext likely areas. A suggest which everybody was sure about was that the car ran perfectly before the customer got his hands on it.


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Figure 1


I felt the the garage was appropriate on track with an ignition time issue, however just hadn’t managed to accurately decide the fault yet. If there’s one thing I preach it’s constantly start at the beginning. If us are managing a timing issue, we need to look at when ignition is occurring and also compare it to crank rotation and piston position.


This engine provides a simple ignition system. The communication of its operation is the the ECM collects details from the CKP sensor and also emits two separate main dwell regulates to a solitary DIS pack.


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Figure 2 mirrors a typical catch with the engine cranking and our error present. Every trace catches were taken with the scope’s usual (black lead) linked to the vehicle’s chassis ground. When capturing a trace, many civilization attach an excellent importance to whereby to rod the red probe without giving ideal consideration what to do with the black probe; yet the high quality of the an outcome relies same on both probes.

Channel A (red) — We watch a great crank rotation and speed v no apparent signal anomalies. This CKP circuit supplies a variable-reluctance sensor with both attached cables transferring the AC produced signal. The circuit is biased at around 1.5 V to help the ECM’s self-check. There are a few traps to beware of: most crucial is to make certain you room monitoring the correct cable, so the you save the check results consistent and trustworthy and constantly with the very same trace polarity. Here both CKP cables will offer very comparable trace patterns, but one will certainly be the inverse of the other and also it’s challenging to phone call which is right and which is wrong for a certain system. Ns probed the White/Red cable, contrasted it to a previously stored known great capture, and it viewed OK.

We likewise can acquire a great visual correlation as the engine attempts come lock from our suspected time error.


Channel B (blue)— The trace is an overwhelming to see however it is there, hiding behind the Channel D (orange) trace, i beg your pardon is odd. I would expect to check out the dwell commands alternating between 1 and also 4, then 2 and also 3, and ago to 1 and also 4 through all regulates being 180° apart through respect to crank position. According to the capture, the cylinder 1 and also 4 dwell duration is developing at precisely same time as the cylinder 2 and 3 dwell period. It likewise seems the the reverse is true; 2-and-3 is developing at the same time together 1-and-4. There’s something not right, and it confirms an ignition time issue.


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Figure 3 shows among the primary ignition pulses indigenous the previous capture in more detail. This is wherein the powerful zoom constructed in to the PicoScope software application comes in handy.

Channel C (green) — At the time of hook-up ns don’t understand what I’m going come find, for this reason it makes sense to acquire as huge a photo as feasible about what is going on, as periodically only one channel trace may prove to be of any kind of value. What clearly needs investigating additional is the existence of both coil primary regulates at the very same time, leading to plugs 1, 2, 3, 4 all to fire together. Go the ECM understand it’s law this? part weird default strategy? possibly the garage to be right: a broken ECM.

I’ve touched on this subject before in other situation studies: when a diagnosis is taking me down the road of a brand-new control unit I gain suspicious that there’s quiet something waiting to it is in found. The next step is to check the pertinent cabling and attached components. Together the circuit illustration earlier shows, this mechanism is straightforward enough for united state to occupational out a check procedure. The ECM power gives were checked and also confirmed even though this yes, really didn’t seem a likely cause of the fault — it was nevertheless still an important step. That wasn’t long, ~ collecting a couple of meter readings, the one certain resistance worth didn’t it seems ~ right.


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With key off, I confirm the circuit resistance in between one DIS major cable and also the other. Ordinarily I would err ~ above the next of caution when taking resistance readings with a manage unit tho connected, since semiconductor susceptibility and meter polarity problems can give false meter readings and also send you turn off on a two-hour ghost hunt. However, v this problem, that was important that I saw what the ECM to be seeing. I intended a low analysis somewhere in the region of 2 ohms, but my analysis was too low.


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Then, v the ECM isolated, I acquired the same 0.5 ohm reading, so this obviously eliminated the ECM together a possible cause. What nailed this error was as soon as I disconnected the DIS fill from the other end and also got the same 0.5 ohm. The coil command lines were shorted together!

This currently made perfect sense and tied cause and effect with each other nicely.


Figure 6 mirrors a hole the was discovered. This to be drilled into the bulkhead — a famous place for routing extra strength cables for in-car entertainment. Twisting ring the engine harness revealed significant cable damage.


Remember the customer’s added inventory put on the car...

Stripping earlier the insulation I discovered that a the majority of cable strands had actually suffered, which supposed that new cabling had to it is in soldered in. With the fix in place, the engine fired up for the very first time in weeks. From below on ns recommended one oil and also filter adjust to remove hefty fuel deposits indigenous the main of cranking, and also a decent run at cruise speed to clear the end the exhaust stream and also regain suitable closed loop and also emissions. Figure 7 shows the trends I was expecting to view earlier.

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Figure 7


Comments

2 comments | add comment


DanSeptember 09 2014


Hi, Nick friend saying that garage changed ckp sensor, coil pack. Right here you say that you diagnosed a shorted coil and also after automobile started???


Hello Nick. I am happy to see much more of your posts. Native time come time I have actually looked for more at Hibtech however have watched nothing it rotates now. Ns am the fellow whom told you exactly how the maritime industry faces metal corrosion; by attaching an additional metal electrically to the piece you want to preserve with one that will certainly sacrificially corrode… you stated you walk not desire to bolt any magnesium (that is great for aluminium) come a Ferrari. Therefore God bless, ns hope things are good.