mgags7

edit: this is for H series engines

Here is the scenario: OBD1 distributors have the ckp, tdc, and cyp sensors all built in. They all read off the exhaust cam, and they go as follows



Tiny pic but you get the idea.

CYP is the first pickup you see with the cap off, it has one point on the shaft that it reads off, to tell the ecu when the #1 cylinder is at TDC.

Underneath the metal plate, there are the other two pickups.
The TDC sensor has 4 points, it tells the ecu when any one of the four cylinders is at TDC.

The CKP sensor reads off 24 points, it tells the ecu exactly where in the rotation the crankshaft is, and will contribute to the random misfire CEL.

On obd2 cars the CKP and the TDC sensors are located on the oil pump housing, and the CKP reads off 12 points, because the camshaft is turning at half crankshaft speed.

I just ran the 4 wires for these two sensors up to the obd1 distributor.

If the engine misfires, the crankshafts position will not be like it normally is after a spark firing, it will lag behind some as it waits for the next cylinder to fire and keep it going. Basically, it fluctuates slightly. The obd2 ecu reads the signal from the CKP and generates the random misfire codes that me, and some other obd2 people who did the wiring conversion get.

I did check my wires and they have zero resistance back to the ecu, so they are not the problem here.

This has happened with multiple distributors so that isn't the problem here either.

My valves are well adjusted, my EGR ports are clean, my ignition timing is fine. The car really isn't even misfiring when the code flashes, or at least it is so subtle that you can't tell.

The code ALWAYS happens on the highway, it will not flash at low rpm, it usually always happens between 3500 and 4000 rpm and a light to moderate load. Going uphill or hitting it lightly to change lanes will cause it to flash.

This isn't a huge problem, other than you cannot pass obd2 inspection here with a CEL on. If it comes down to it I can just drive around at low rpm until the car's readiness codes are set, then go get it inspected. First though, I would like to figure this out, i have a buyer for my car but he wants the CEL gone....

Switching to the obd2 stuff is my very last option here. I do NOT want to deal with taking all that **** off the side of the engine, buying an oil pump and sensors, putting all that **** in. Then I would have to buy an obd2 distributor, undo my wiring changes, get the external coil, ugh it would be a nightmare.

Thanks guys
-Matt


Modified by mgags7 at 6:47 AM 9/4/2007

mgags7

anyone?

RC000E

Whoa....whoa whoa......your are spitting out some type of fact based statements, and they are not correct. What motor are we talking about here?

On D's and B's the three sensors in the OBD1 dizzy are the same THREE that are in the OBD2 dizzy. The obd2 cars have a crankshaft fluctuation sensor that is mounted down by the oil pump, and this is what allows the OBD2 ecu's to sense random cylinder misfires. If you do an OBD conversion, you just ditch that sensor entirely because the OBD1 ecu's don't look for it or give a damn.

The OBD1 ecu's don't even kick a random cyl misfire code either, so basically your post has me highly lost? Apparently we aren't talking about a D or a B, so what the hell motor is this?

Also, what code SPECIFICALLY and what ECU are you running at this point?


EDIT: Well, I see your referring to an H series. Just to be clear for readers, "ALL" OBD2 dizzy's are NOT like this.

So, to be clear, your getting a cylinder misfire code from a P13?

onepoint6i

i was thinking the same thing....

i have converted a (B-series) obd 2 dist to obd 1 via swapping pins and plugs...worked perfect..

mgags7

yes, it is a p13, and the prelude never came with a crank fluctuation sensor.

I was kinda wondering about not having that and where it was getting this code from...

It will throw any one of codes 71-74, random misfire cyl x.

thanks

RC000E

Well, if you check the Factory DTC listing for the P13, the ecu isn't designed to output a code in that range....so.....I don't really see what explanation there is. Something doesn't add up here.

Is this a US or JDM p13?

Can you sense a misfire when driving the vehicle in these specific scenarios such as changing lanes or going uphill?

Can you attempt to reproduce this condition, then immediately shut off the car and do a plug read? If you feel there is a true misfire condition, then I would just set the code aside and do a typical misfire troubleshoot, doing basic ignition system maintenance, and ensure that basic fuel system in order.

mgags7

US 1996 P13

The car doesn't actually misfire as far as I can tell. I'll read the codes out for you the next time it happens, which shouldn't be hard to reproduce, but it was def. 71-74 last time.

mgags7

I already have done a pretty thorough misfire troubleshoot, including new plugs, new ngk wires, changed distributors, measured fuel pressure (it was fine) and I have a new fuel filter ready to go in today as a last resort.

Like I said I cleaned the egr ports and checked the ignition timing as well, as I found that other people had problems with random misfires that ended up being related to those problems.

bump

RC000E

Alright alright I got you. I thought you were converted back to obd1 and getting obd2 codes, but I see now, the only thing "converted" was the OBD1 dizzy in order to function with the OBD2 system.

My only guess, aside from the misfire condition actually occuring, is that there is some type of pulse resolution difference between the OBD2 sensors and the OBD1 internal dizzy counterparts.

This is generally never an issue in D or B dizzy's from differing OBD gens, but in this case due to such a different type of system it could be the case. Especially since you mention other converters experience this problem as well.

Shielded wiring maybe also? Factory wires of this nature have ground shielding, maybe some type of interference. It sounds unlikely though because the dtc is triggered under specific conditions you've identified.

Are you certain that the sensors from both OBD's are referencing the same degree points in the crankshaft rotation? Since the ecu uses that sensor for timing advance and injector duration, could it be affecting timing possibly?

Try going to a parts store and borrowing their OBD2 scanner (advanced auto parts lends out a pretty descent one) with datalogging and set a recording trigger for when a dtc is encountered...maybe you can pick up the issue that way.

mgags7

Yeah that is the only explanation I was able to come up with also. The crank reluctor has wider pickups so maybe the pulse width is off, then again that seems like it would be a more constant problem and not so specific to one condition.

I think noise across the wires is a definite possibility, since it usually happens at one rpm, there is a frequency at which noise across those wires is going to be "worst" and 4000rpm or so may be that number.

Thanks for the help

RC000E

yeah, if you locate a solution, post it up man....good luck with that.