96 850 turbo #5 misfire

jeandy · Post by **jeandy** » 07 Dec 2017, 20:29

Hi All,
I hope you can help. I have owned my 96 850 Turbo for 11 years. Has 154,000 miles. I recently drove it harder than usual and the next day the check engine light came on. Code came back for cylinder 5 misfire and undefined misfire code. Both the Snap On and Alltell scan tools tried on it would not give live data. Wires (8 years old IPD) were showing some arcing so were replaced with Bougicord wires and OE Bosch plugs, cap & rotor. No change. Compression check showed 170 psi in 1,3,4,5 and 180 psi in 2. Next was a Seafoam drip into the engine. Other than the engine feeling smoother and faster on acceleration the miss was still there. Occasionally a bank one rich code would come in. Next we swapped injector one with five and no change in cylinder 5 misfire. Car gets full or semi synthetic oil and always gets premium fuel. Gets good daily driver runs. Am out of ideas. Ordered a coil although that does not seem likely. The misfire will randomly get better for a couple minutes. Feel it more at idle. Better in park at stop signs than in drive. Please any ideas. We really thought it would be the head written about in many other threads. Thank you.

Post by **erikv11** » 07 Dec 2017, 22:51

Here are the top suspects that come to mind, in approximate order of suspiciousness:

- the intake manifold gasket may be failing at the corner, and there is a small vacuum leak into #5. More common after PCV service, but can happen with age too. Check it by spraying starting fluid into the area with the engine running. If the idle surges, there is a vacuum leak. Heck, check all around the IM gasket, even check the vacuum tree etc.

- the wire from the crank position sensor is too close to the coil wire (this happens a lot!)

- the wire from the crank cam sensor is too close to the coil wire (less common problem)

- the timing jumped a tooth when you ran it hard. Check the timing marks.

Post by **RickHaleParker** » 08 Dec 2017, 16:14

The pulses from the ECM that fires the injector is the only thing electrical that is unique to cylinder #5.
Did you check the connector to the #5 injector?
If you have an LED auto logic probe, did you check the pulses at the #5 injector? .... Gray/White wire.

Post by **erikv11** » 08 Dec 2017, 16:23

RickHaleParker wrote: ↑08 Dec 2017, 16:14 The pulses from the ECM that fires the injector is the only thing electrical that is unique to cylinder #5.
Did you check the connector to the #5 injector?
If you have an LED auto logic probe, did you check the pulses at the #5 injector?

Actually, the pulse to #5 is *not* unique, in fact there is only one pulse from the ECM: all five injectors fire at the same time, from the same pulse. It could be the #5 injector wiring though, the wiring is unique, so your point is not wasted.

A simple way to test this is to pull back the wire loom so you have enough wire length to swap injector plugs, between #4 and #5. I'd definitely do that. No special tools required.

Post by **RickHaleParker** » 08 Dec 2017, 16:46

all five injectors fire at the same time, from the same pulse

Buzz! ... completely incorrect.
All five injectors do NOT fire at the same. You never hear of a firing order?
There are five injector control lines from the ECM, one for each injector.

Post by **erikv11** » 08 Dec 2017, 17:10

RickHaleParker wrote: ↑08 Dec 2017, 16:46 all five injectors fire at the same time, from the same pulse

Buzz! ... completely incorrect.
All five injectors do NOT fire at the same. You never hear of a firing order?
There are five injector control lines from the ECM, one for each injector.

buzz??

Actually, it's unusual for me but, completely correct! The procedure is called "batch injection," and this platform uses it. Batch injection is actually very common. Check it out!

The term "firing order" is a concept not some dogma for how injector pulse management works. Firing order here is only relevant to the spark sequence, whether achieved by the rotor (this car) or the ECM (coil-on-plug engines).

Yes there are other engine management systems use separate pulse injection signals, but Motronic m4.3 (93-96) and m4.4 (96-98) are both strictly batch injected.

Post by **RickHaleParker** » 08 Dec 2017, 17:15

Are you really that ignorant, just trolling or both?

Post by **erikv11** » 08 Dec 2017, 17:59

Ignorant ? Troll? i will resist being a jerk ...

I’ve told you how it works I’m not going to do the google search for you too, but you may want to learn about the differences between *batch injection* (the way it works on these cars) and *sequential injection* (the way most people would guess it works). It is surprising but true, batch injection is extremely common.

It was a good suggestion on your part - it could be the injector wiring and it is easily tested!

Post by **RickHaleParker** » 08 Dec 2017, 18:05

Both for sure.

jeandy · Post by **jeandy** » 08 Dec 2017, 19:18

Hey All. Thanks for responding! I will try the suggestions. I hate driving the car like this and techs are frustrated too. Update. Was able to reset the codes and although the miss feels strong at idle, less so at hwy the CEL has not gone back on yet. So frustrating that it gets stronger/weaker at will. Will follow up next week.