Rpm tach problems. . .

[nightspeed87]

Im currently running a 1990 ecu for eprom chipping purposes.
I had to switch pin 6 and 14 I believe to make it work with my 93 harness.
The ecu works fine and have been driving with it for a few months and my only problem right now thats bothering me besides a check engine light that comes on randomly is my stock rpm gauge wont work.
Well i have done a search and found that the 90s ecu uses different rpm signals or different grounds or something meaning
the stock 93 tach wont work on a 90s ecu. The funny thing is; is that it works when i first turn the car on then after about 2 minutes it doesnt work anymore for the rest of that driving session. Why would it even start to work at all though? I even hooked up an aftermarket autometer
tach/ w shiftlight to see if I could get that to work in its place and I hooked it up correctly
and hooked up the signal wire to the white wire on the transitor harness next to the coil pack and it works 60 percent of the time and the other 40% it will start jumping around and sticking at one rpm number and not moving. Both tachs always seem to work on first start up then sometime during driving just stop working..
Why would the manually connected aftermarket tach exibit problems aswell if it was hooked up correctly? Any ideas on how to get either of these working correctly?

Also one more thing id like to add to this thread instead of starting another one would be that my car doesnt always like to start right up.
Ive considered it being the starter, but the thing is, on cold startups it cranks just fine with no hesistation.
After its at operating temperature and Ive been driving it for a while if I turn it off and then go to turn it back on it just rotates and doesnt start unless
I give it some gas. Why is that? I dont have a fuel pressure solenoid and I hear those help with warm starts.... Could this be the culprit?

 

[luv2rallye]

These may help although they are the other way around: http://www.dsmtuners.com/forums/showthread.php?t=210441 and
http://www.ecanfix.com/users/mdhamilton/ecuconversion.html. PM the expert Steve for complete info.
Yes the fuel pressure solenoid helps on warm starts by raising fuel pressure to decrease vapor lock.

 

[nightspeed87]

I was starting to wonder if a lightened fidanza 8lb flywheel could have anything to do with hard starts? So its safe to assume that the hard starts where I need to give it gas are related to not having the fp solenoid. I have two friends who dont have fuel pressure solenoids and there cars dont start as sluggishly as mines. Mines starts like its just being woke up after a long time and its yawning or something .

That link has some good information but was a little confusing as far as turning 90s harness/ecu to work with 91+ and I couldnt quite follow how to do it in reverse for my situation.
And why does the after market tach work randomly?
Shouldnt that have nothing to do with the ecu messing up the stock one?
Or could there be another wire i can hook the aftermarket one up to to fix it.
I only need one of them working correctly....

 

[steve]

There is nothing involved to make the factory tach work when running a 90 ECU in a 91+ car. It's just does so if you haveing problems it not directly related to having a 90 ECU. You do still have to swap pins 6 and 14 for fix the idle issues caused by having the IPS and MAF reset pins swapped.

Without describing how the aftermarket tach is connected we have nothing to go on.

Steve

 

[nightspeed87]

There is nothing involved to make the factory tach work when running a 90 ECU in a 91+ car. It's just does so if you haveing problems it not directly related to having a 90 ECU. You do still have to swap pins 6 and 14 for fix the idle issues caused by having the IPS and MAF reset pins swapped.

Without describing how the aftermarket tach is connected we have nothing to go on.

Steve

Ok thanks steve that cleared up a lot and a little.
Well the stock rpm tach isnt working 95 pecent of the time, it tends to work when I first start it but shortly after it will discontinue working.
The after market rpm tach, I have the red wire ran to the fuse box ( hotwire ) the black wire grounded on a nearby screw to the chasis, and I believe the green wire which was the signal wire I have connected to the white wire on the transitor.
( The bigger plug under the smaller one that plugs into the back of the block to the right of the coil pack. ) I was told the white wire was the rpm source.

Now the aftermarket tach works like 60 percent of the time and will discontinue working;
though Lately its been working less than that. When it stops working it just jumps to whatever number the shift lights set for and stays there, and maybe will flicker here and there every once in a while. I was thinking maybe its the ground but
the light bulb in the tach stays on even while the tach needle isnt correct.... Any ideas now.?

 

[wvturbo2]

My Rpm's jump around if i give it a decent bit of throttle around 4k my rpm's jump from 4k down to 1k and back up higher. What could cause that. I have a chipped eprom as well.

iwas told it may be as simple as using a different power transistor that has the right logic circuit for the tach. They also recommend talking to sa company that sells chips.

 

[nightspeed87]

My Rpm's jump around if i give it a decent bit of throttle around 4k my rpm's jump from 4k down to 1k and back up higher. What could cause that. I have a chipped eprom as well.

iwas told it may be as simple as using a different power transistor that has the right logic circuit for the tach. They also recommend talking to sa company that sells chips.

yea mines jumps around like this too but eventually ends up just sticking in one place. I cant figure out why its doing that , the aftermarket one I tried does it, and the stock one. Its annoying.

 

[wvturbo2]

The best part is NO 1 knows how to fix it. I want to hook my wideband up and see if the afr changes, maybe im still running to rich or lean. I have a thread like this on buschur and it died no1 has been able to answer me. I wish more than anything i could find an answer. Maybe talk to someone who sells eproms.

 

[steve]

Now the aftermarket tach works like 60 percent of the time and will discontinue working. Any ideas now.?

Does the car start acting like it's missing when this happens or is it running well but the tachs are acting up?

You have both the factory tach and the aftermarket one connected to the same signal source. It comes from the power transistor logic taking the signal from each coil and combining them.

If you have a datalogger it would also help to know what the ECU says the RPM is when this is happening. It uses the CAS signals to figure RPM.

Steve

 

[wvturbo2]

mine goes all crazy and car runs fine no knock. Though occationally throught it ill get a bit of knock. I couldn't tell when, because of the jumping

 

[nightspeed87]

My car drive normal besides the sluggish start ups and it always does it.
I talked to jeff at keydiver and he said the 90s ecu should have no effect on my 93 harness and that the ecu only use the rpm to throw a cell with something to do with spark or what not. He told me try unplugging pin 109 out the ecu and tellin him the results. I havent gotten around to doing that yet though. Im about to try it. Before I do through does any one oppose, or will this is a bad idea just pulling that pin out and leaving it out.?

My stock rpm tach mainly doesnt work at all..
The aftermarket one jumps around all crazy and then finaly stops moving
and just sits to wherever the shift light point was set with no further motion like its dead.
Im sure it has something to do with the signal wire because its grounded right and wired up right.
The stock one always worked before changing over ecus though???

 

[wvturbo2]

My is normal til i get on it then it jumps around. See what happens and get back to me. Also how did u get ahold of him ?

 

[steve]

I talked to jeff at keydiver and he said the 90s ecu should have no effect on my 93 harness and that the ecu only use the rpm to throw a cell with something to do with spark or what not. He told me try unplugging pin 109 out the ecu and tellin him the results.

Pin 109 is the input to the ECU for confirming that the power transistor/coil fired. If the ECU doesn't see a change right after it fires the coil it throws a CEL. The factory tach connects to this as well. I've run 90 ECUs in my car (91) and had others do so (91+) without any tach problems. There were all known original cars as far as the rest of the ignition system. No JDM engine swaps or aftermarket tachs installed.

So Jeff agreed that this should just work, unlike the well know problems of using a 91+ ECU in a 90 car that wvturbo seems to have.

Steve

 

[nightspeed87]

so by un plugging this pin 109 will it cause it to throw a cell;
not that i dont already have a cel on. and will unplugging this cause the engine to run bad or harm anything else in any way?

 

[steve]

not that i dont already have a cel on.

That's kind of an important little detail, don't you think?
What code(s) is the ECU throwing?

Steve

 

[wvturbo2]

Mine is supposed to be a 90 eprom, but my friend swapped the pins. Would swapping the pins cause this or should i swap them back. The car was running to rich before and wouldn't run right thats why the pins were swapped. Let me know. Also Steve don't you do custom chips ? I've heard good stuff about you.

 

[nightspeed87]

That's kind of an important little detail, don't you think?
What code(s) is the ECU throwing?

Steve

I dont have a logger and I didnt want to assume nothing because Ive always had
a cel since I had the car even when the tach worked.....


I just talked to jeff again and he said when he chipped my ecu I always had acid damage on the 90s ecu due to caps leaking and he fixed it and cleaned it up but he told me before that he thought I had short time on that ecu from already done damage?
Later on im going to buy another eprom and have it chipped from him but curious if this would affect the tach? But probably not since the ecu doesnt have anything to do with the rpm signal right...

Tommorow ill pull out pin 109 and see the results.
Jeff also asked about a grey cylinder shaped capacitor thats suppose to sit on the intake manifold because hes noted that hes had issues with turbo cars having tach problems
with this little thing because its like a sound/ intereference deadner for the tach pulse.. ?
Could this be confirmed...

 

[nightspeed87]

Mine is supposed to be a 90 eprom, but my friend swapped the pins. Would swapping the pins cause this or should i swap them back. The car was running to rich before and wouldn't run right thats why the pins were swapped. Let me know. Also Steve don't you do custom chips ? I've heard good stuff about you.

your suppose to swap pins 6 and 14...

http://vfaq.com/mods/ecu-harness-1G.html
http://vfaq.com/mods/ECUs.html

 

[wvturbo2]

He swapped the right pins but the eprom was supposed to be a 90 thought i dont know if they were swapped for a 91 prior to my car. My take is fine til i start getting on it then it goes nuts. On the knock sensor for stock boost gauge iim guess -7 is 0. I'm just wondering how much knock would be around 0 or something. It jumps up sometimes, but not often/

 

[nightspeed87]

He swapped the right pins but the eprom was supposed to be a 90 thought i dont know if they were swapped for a 91 prior to my car. My take is fine til i start getting on it then it goes nuts. On the knock sensor for stock boost gauge iim guess -7 is 0. I'm just wondering how much knock would be around 0 or something. It jumps up sometimes, but not often/

I dont know because I currently have an n/t gauge cluster ( long story- in which shouldnt be related to my tach problem because the n/t gauge cluster used to work before with the rpms. ) but for your situation to tell if the wires are on the right spot look at the ecu diagram and see what color wire
controls what and if you see the wrong color wire in the wrong pinout between 6 and 14 which were potientially out of order then you know thats your problem.

 

[steve]

He swapped the right pins but the eprom was supposed to be a 90 thought i dont know if they were swapped for a 91 prior to my car.

Go look and see what color wires you have running to pins 6 and 14. Also look and see what the part number is for your ECU. You should also check the number printed on the edge connector to make sure the case and ECU board match.

Steve

 

[steve]

I don't have a logger and I didnt want to assume nothing because Ive always had a cel since I had the car even when the tach worked.

Don't assume anything then. You don't need a logger to read the error code.

http://www.vfaq.com/mods/wayback/BradBauer/electrical/code.html
http://www.ecanfix.com/~mdhamilton/errorcodes.html

'90 cars have noise filters in the ignition pulse detect (tach) signal. I haven't seen anything other than the condensor on the coil power on the later cars.

I'd also try putting the ECU into another car and see if the tach acts up.

When did you put a NT cluster into the car and why?

Steve

 

[wvturbo2]

ill check tomorrow since its my day off.

 

[nightspeed87]

well i pulled out pin 109 and the tachs been working ever sense.
Both tachs started working immediately and hasnt shown sign of failing yet, its not bouncing around or sticking in one place any more... I wonder why?
And ive read the noise filters are only for 90s because the 91-94 trans/coilpack has it built in.


wvturbo2, try what I did and pull out pin 109. Its a white wire on the smallest plug in the ecu, its the second one to the right on the bottom if the plugs clip in is on the top.
Its next to a black and white wire.

 

[wvturbo2]

Do u just leave it out ?