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Fresh motor rebuild falls of a cliff at 5500rpm


Kirkster

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So I got my rebuilt motor back in the car and have been having issues with it generating power above 5500 rpm.

 

I am running a MS3 Pro with full sequential injection and ignition with GM D581 coil packs. For the first year or so it ran well with a mystery motor. 160WHP 150tq. Then that motor lost compression in cylinder 4.

 

Which led me to a rebuild over the winter, I had planned on a Rebello motor but suddenly we became a one income family and plans changed.

 

So I had it bored .040 over and dished .040 over pistons put in as well as having the head gone over and springs replaced.

 

I dropped it back in and got things running and broken in and then took it to my tuner. He ran the motor in a bit more on the dyno before the first pulls and upon the first real pull the torque basically falls off a cliff at 5500 rpm. We did a few more pulls with the same results. My tuner then went through the tune to make sure everything was ok with the computer. We then did a valve job on the dyno and all the valves were tight, once they were adjusted we did a couple more pulls with the same result.

 

So now I have had my injectors cleaned and flow checked and they needed it done and now the engine runs much smoother, I have also rewired the coil packs since I initially had them wired as LS1 coil packs where they needed to be wired as LS2, this led me to chop off the old connectors and put on some LS2 -rewireed pigtails which I was concerned could be contributing to the problem. Hence the rewire.

 

So it ran well when I fired it up but when I took it for a spin it crapped out at 5500 rpm again.

 

So now I am stumped. The only thing that changed outside the motor is that I am running a webbed NA intake out of a 280 instead of the group buy intake (which would be perfect if I could run a turbo). I am Also running a 65mm throttle body instead of the old 80mm.

 

What could be causing the motor to fall off a cliff at 5500 rpm???

 

Not sure where to look next....

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What is the HP doing at High RPM's ? Torque and HP cross at 5,250 RPM after that Torque will decrease in reason to RPM. It is normal for Torque to fall off at high RPM's, particularly with a stock camshaft. How much things drop off is a mater of interpretation... it may be perfectly normal, or it may be a problem. If the Dyno operator is not familiar with Datsun motors, he may not have a a good idea what is Normal.

 

Do you have a Dyno pull on the engine previous to this where the power, did not drop off as drastically? Stock cam is pretty mellow, and a stock L28 does tend to go flat after 5,500. Posting your present and previous Dyno charts would help. Should be from the same Dyno to make any real intelligent..... but any Data is helpful

 

You mention you had the valve springs replaced? That raises a flag. What brand were they and what rate? Did you replace both inners and outers? Some aftermarket replacements are way below the Nissan OEM spec. Just poor quality.....

 

What was the AFR curve reading at the top end. Your Dyno operator should have been measuring that.

 

BTW, wording like " it crapped out again above 5,500 rpm " is not very helpful. Did it start to misfire? Did it start to run rough? What did the AFR do? Was the Trigger signal monitored to see if it was breaking up or getting mis-counts? All of this should be monitored on the Dyno when you do your pulls. You should be logging the MS 3 Pro with Tuner Studio the whole time.

 

What Ignition timing where you using. ( Total mechanical )?  What Octane and Brand fuel?  Plugs and Heat range? Detonation will cause Torque and HP to plummet... just one of several things that could be wrong. But you must have the data to analyze..... and your Dyno operator has to know how to interpret that Data. 

Edited by Chickenman
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Just thinking out loud... so bear with me. A few things that can cause Ignition issues.

 

Are the D581's genuine GM/AC Delco coils or aftermarket brands? Some of the aftermarket brands are of poor quality and tend to Auto-Dischrage. This usually happens if Dweel settings are pushed too high and/or Plug gaps are too large. What is important to realize is that once coils have Auto-Discharged, they are usually hooped. Internal circuitry gets damaged. It's a steady spiral downhill after that... 

 

Dwell should be limited to no more than 4.5ms and Spark plug gap should be no more than .045". Running more than those figures over heats the coils and slowly fries them. You cannot run a straight 4.5ms all the time. There is a Dwell Table for GM Coils that utilities the MAP signal to cool the coils when the engine is not under high load.

 

You need a clean and strong signal from your Crank sensor at high RPM's.  Tuner Pro can help you monitor that.  If you're  using a Crank Trigger wheel check your air gap. Or are you using the Z31 CAS? What Trigger wheel in that if you are?

 

Crank and Cam Trigger lead wire must be shielded and routed well away from Spark Plugs leads and should also be not be run parallel  to any 12V leads. I don't know if the MS3 Pro  wiring harness actually uses shielded Trigger wires. They may only be twisted pair. Motec and Haltec always use twisted pair wires inside of a shielded casing. That's the best way to do it. MSD makes shielded Trigger wiring harnesses in various lengths.

 

Plug leads are very important. You must use a good quality Spiral wound leads for the coils. MSD or Magnacore are very good. Beware of Taylor and Accell house brands. There lower cost items are junk.  Note. You cannot run Solid Copper leads or Graphite leads with stand alone ECU's. These generate too much EMI, even with short plug leads. Resistor plugs should be used as well. 

Edited by Chickenman
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What is the HP doing at High RPM's ? Torque and HP cross at 5,250 RPM after that Torque will decrease in reason to RPM. It is normal for Torque to fall off at high RPM's, particularly with a stock camshaft. How much things drop off is a mater of interpretation... it may be perfectly normal, or it may be a problem. If the Dyno operator is not familiar with Datsun motors, he may not have a a good idea what is Normal.

 

Do you have a Dyno pull on the engine previous to this where the power, did not drop off as drastically? Stock cam is pretty mellow, and a stock L28 does tend to go flat after 5,500. Posting your present and previous Dyno charts would help. Should be from the same Dyno to make any real intelligent..... but any Data is helpful

 

You mention you had the valve springs replaced? That raises a flag. What brand were they and what rate? Did you replace both inners and outers? Some aftermarket replacements are way below the Nissan OEM spec. Just poor quality.....

 

What was the AFR curve reading at the top end. Your Dyno operator should have been measuring that.

 

BTW, wording like " it crapped out again above 5,500 rpm " is not very helpful. Did it start to misfire? Did it start to run rough? What did the AFR do? Was the Trigger signal monitored to see if it was breaking up or getting mis-counts? All of this should be monitored on the Dyno when you do your pulls. You should be logging the MS 3 Pro with Tuner Studio the whole time.

 

What Ignition timing where you using. ( Total mechanical )?  What Octane and Brand fuel?  Plugs and Heat range? Detonation will cause Torque and HP to plummet... just one of several things that could be wrong. But you must have the data to analyze..... and your Dyno operator has to know how to interpret that Data. 

 

Ok,  The torque is not falling off, it is taking a 90° nose dive.  I sent my tuner (Peter Florance) an email asking for the Dyno sheets from the last Dyno session as well as the first session with the car for a comparison.  It is all on the same Dyno at Abacus Racing in VA Beach.  

 

I have a Wideband in the car and we did do a comparison between the exhaust tip ARF and the one in the car and they were within a couple % of one another so we in general use the one in the car when tuning.

 

There was no trigger loss at high RPM.  None in the counter on the TunerStudio gage cluster, and no cut out of the motor like last year.

 

I know what this feels like since I had a crank sensor flake out last year and cause me all kinds of grief running it down.  So this year I changed from the threaded sensor to the plastic body sensor with the mount tab on the end.  it is able to have a larger gap than the threaded sensors and still work properly.  My threaded sensor last year had a very tight gap and ended up being temperamental.  

 

Running 93 octane fuel (sunoco I think), the plugs were gapped properly when installed in the car,  Since this is a low compression engine we don't think there is any detonation issues (we did not hear any and Peter does know what to look for)

 

I can send you the log file from today if you want it.  This was after I changed the fuel filter element for a clean one.  (the old one was not particularly dirty but figured that it could not hurt to change it out)

 

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Just thinking out loud... so bear with me. A few things that can cause Ignition issues.

 

Are the D581's genuine GM/AC Delco coils or aftermarket brands? Some of the aftermarket brands are of poor quality and tend to Auto-Dischrage. This usually happens if Dweel settings are pushed too high and/or Plug gaps are too large. What is important to realize is that once coils have Auto-Discharged, they are usually hooped. Internal circuitry gets damaged. It's a steady spiral downhill after that... 

 

Dwell should be limited to no more than 4.5ms and Spark plug gap should be no more than .045". Running more than those figures over heats the coils and slowly fries them. You cannot run a straight 4.5ms all the time. There is a Dwell Table for GM Coils that utilities the MAP signal to cool the coils when the engine is not under high load.

 

You need a clean and strong signal from your Crank sensor at high RPM's.  Tuner Pro can help you monitor that.  If you're  using a Crank Trigger wheel check your air gap. Or are you using the Z31 CAS? What Trigger wheel in that if you are?

 

Crank and Cam Trigger lead wire must be shielded and routed well away from Spark Plugs leads and should also be not be run parallel  to any 12V leads. I don't know if the MS3 Pro  wiring harness actually uses shielded Trigger wires. They may only be twisted pair. Motec and Haltec always use twisted pair wires inside of a shielded casing. That's the best way to do it. MSD makes shielded Trigger wiring harnesses in various lengths.

 

Plug leads are very important. You must use a good quality Spiral wound leads for the coils. MSD or Magnacore are very good. Beware of Taylor and Accell house brands. There lower cost items are junk.  Note. You cannot run Solid Copper leads or Graphite leads with stand alone ECU's. These generate too much EMI, even with short plug leads. Resistor plugs should be used as well. 

 

The Coil packs are genuine AC Delco D581s  the plug leads are Magnacore 60285,  not sure about the plug brand but the gapping was set at .035 when the plugs went into the car

 

Not currently running a dwell table in the settings.  the dwell is set to 3.0ms and the spark is set to 0.9ms.

 

The crank and cam trigger wires are routed separately from the rest of the wires in the car as I was paranoid about EMI.  The wires are shielded, and the MS3Pro has a shielded Cam and Crank wires in the factory harness which is what the shielded crank and cam wires that I put in are connected to.

 

I will be taking the car over to the motor builder tomorrow to have him look things over.

 

I will post up the dyno sheets when Peter sends them over to me.

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Don't the MS logs show what spark and injectors are doing?  You talk about falling off a cliff and crapping out but nothing about what the logs show.  That's the beauty of data-logging, you don't have to guess at what happened, only what caused it to happen.

 

Fun to review all of your specs. but the logs should tell you what's (not) happening.  Spark and injector open duration.

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Don't the MS logs show what spark and injectors are doing?  You talk about falling off a cliff and crapping out but nothing about what the logs show.  That's the beauty of data-logging, you don't have to guess at what happened, only what caused it to happen.

 

Fun to review all of your specs. but the logs should tell you what's (not) happening.  Spark and injector open duration.

Sent the logs to Peter, I let the log viewer update when I opened it today and now it's not working... Doh...

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The Coil packs are genuine AC Delco D581s  the plug leads are Magnacore 60285,  not sure about the plug brand but the gapping was set at .035 when the plugs went into the car

 

Not currently running a dwell table in the settings.  the dwell is set to 3.0ms and the spark is set to 0.9ms.

 

The crank and cam trigger wires are routed separately from the rest of the wires in the car as I was paranoid about EMI.  The wires are shielded, and the MS3Pro has a shielded Cam and Crank wires in the factory harness which is what the shielded crank and cam wires that I put in are connected to.

 

I will be taking the car over to the motor builder tomorrow to have him look things over.

 

I will post up the dyno sheets when Peter sends them over to me.

 

3.0ms at the top end might be a bit low. Even the stock GM Silverado Dwell Table runs higher than that. You could temporarily bump the Dwell up to 4.0 to 4.5ms and see if that cure the drop off. Do not run 4.5ms as a constant though. Only for testing.

 

Do run a Dwell Table. It is necessary to utilize the coil cooling strategy and maximize spark. Here is a picture of the stock GM D585 dwell table. D581 coils should be similar. RPM and Voltage Correction Table:

 

7979972765_d598e5b748_z.jpg

 

The Audi/VW Turbo guys are using 4.2 to 4.5 ms up on top with 30 psi boost. They've been doing it reliably for a number of years. Here's a link to a thread I started on VWVortex.com. Very technical and fantastic input from some very knowledgeable people. It is now 25 pages long and growing......

 

Check out Spartiati's Dwell table on Post #1 of the following link.. This is an aggressive table for a high boost car, but also a safe level.

 

http://forums.vwvortex.com/showthread.php?5563383-LS2-Yukon-coil-conversion&highlight=LS2+Coil

Edited by Chickenman
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And Fixed.....

 

Turns out that once I had the injectors cleaned, and flow tested they were dumping way too much fuel.  I sent the data logs to Peter and he said, "wow looks really rich now",  He sent me a new fuel map and I drove it and Data logged it.  Reved to 6K with no problem before it was running really rich.  Sent him the data logs and he sent a another new fuel map and a new ignition map.  Now it revs and pulls hard all the way to 7K.  

 

Now it will be off to see Peter in VA Beach for some Dyno fine tuning.  

 

Glad this ordeal is over (of course it is BSP so something else will break).  Really stressing me out, and a great birthday gift!!!

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How did your "tuner" miss that?

 Yeah that has me scratching my head as well. Any decent Dyno operator should be monitoring AFR and should have seen it go pig rich. All that was mentioned in original Post was that In car AFR meter and Dyno AFR were reading the same. No figure was given.... I kinda figured the AFR's were good or something would have been mentioned.... Hmmmm.

 

 

I dropped it back in and got things running and broken in and then took it to my tuner. He ran the motor in a bit more on the dyno before the first pulls and upon the first real pull the torque basically falls off a cliff at 5500 rpm. We did a few more pulls with the same results. My tuner then went through the tune to make sure everything was ok with the computer. We then did a valve job on the dyno and all the valves were tight, once they were adjusted we did a couple more pulls with the same result.

 

I have a Wideband in the car and we did do a comparison between the exhaust tip AFR and the one in the car and they were within a couple % of one another so we in general use the one in the car when tuning.

And no one noticed it was Rich on the Top end? Very strange... how was that missed? Confusing timeline...

Edited by Chickenman
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The injectors were only cleaned last week. The car was last at the dyno in April. The injectors were not flowing enough fuel in their clogged state in April on the dyno once the car was in the upper RPMs... So when clean high flowing injectors were installed it was flowing way too much fuel for the fuel map that was in there that tried to compensate for poorly flowing injectors...

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