I had thought I knew all about the electrical systems but this one has me hogtied. The engine will stall when rolling to a stop after driving and will not refire.

Here's the basics:

• Rebuilt engine, reputable builder, streetport, unbreakable apex seals, coated housings.
• M2 Stage III ECM, SMIC, down pipe, air box.
• All stock control system (solenoids, turbos, electricals)
• Solenoids tested with vacuum and power
• AWS blocked off
• Hose Techniques kit
• New check valves throughout from Malloy
• SR Motorsports light flywheel with ACT clutch
• EM and Engine wire harnesses unwrapped, inspected, fixed and rewrapped
• Fluidyne radiator
• Grounding system upgrade
• Injectors cleaned and flowed by RC - returned indicating "excellent" pattern
• Racing Beat single exhaust
• Back Cat stock.
• All other engine controls and emission devices as stock.
• Replace all gaskets with Mazda gaskets

Here is what's happening:

• Motor starts and idles with a normal agressive tone due to the porting when cold
• Idle is 900 rpm and stable
• Vacuum at idle is between 11 and 13 in Hg
• Drive away is smooth with very smooth acceleration through the gears.
• Highway speeds (50-75) are very uneventful and smooth in 4th and 5th.
• Pulls on boost are strong, very strong and predictable. Haven't pulled at maximum boost nor over 6000 rpm - still running the engine in. Boost pattern is right on for the M2 stage III specs.
• The problem is after driving and a good heat up the engine will stall when rolling to a stop and will not restart (had to have it towed twice now)
• No codes flashed on the CEL
• Engine temps are normal
• Oil pressure is normal.
• TPS in spec
• Throttle body correctly set up.
• Engine will crank all day but no joy (battery good and clutch swith obviously OK)
• New plugs (NKG Plats) again today but it stalled again.
• Put jumper from F/P to ground and the fuel pump is flowing normally.
  
  I'm going to run the diag on the ign system but any help or knowledge into this situation would be greatly appreciated!
  
  THANKS!!

I am going to go through Section F again..... but don't expect any suprises....

 

Have you checked the compression hot? Low compression can prevent (re)starting.

 

Cold compression is:
Front - 75 and 65-65-65
Rear - 82 and 65-65-65

Hot compression is:
Front - 83 and 67-67-67
Rear - 92 and 70-70-70
(note compression gauge may not be accurate but readings are consistant)

Checked narrow range TPS again and found at 1.38 V - reset to 1.00 V
Neutral SW checkout is OK
1-2 SW checkout is OK
IAC is controlling bypass air OK
After a couple of fan cycles in the shop (temp is 210 F) noticed a ticking noise in cat???

Still -nothing makes sense on why it would stall and not restart after driving?

 

Is it flooding when it dies? Does it just spin really fast?

 

Do I assume correctly that you measured that on a standard compression tester, not a rotary-specific one? I don't remember how those readings relate to what you would get on a rotary-specific tester.

IIRC, in working with piston engines, when an engine's compression was low, the engine would more likely start (cold or warm) with a rich mixture but not with a lean one. The cold map on most rotaries is much richer than the hot map. Maybe that relates to your problem.

 

If it's just flooded (and only flooded, nothing else wrong), push it and pop the clutch. It will start immediately if you get up enough speed. I've probably flooded an Rx-7 over 100 times. The 2nd gen cars are very prone to flooding on stock ECU, even if the motor is healthy.

The stalling could be a dirty ISC valve or a misadjusted idle. Since you have a chipped ECU you should try resetting the idle according to the service manual procedure.

 

QFT regarding the FC's flooding tendencies.

To the O.P.: Has the car EVER worked right, meaning is this a new thing or has it been this way since you put it back together?

 

Arghx - Indeterminate on the flooding but don't think so; tried the "deflood" procedure multiple times without success. When the engines cools to ambient it will refire no problem. Also tried partial throttle cranking as if too lean but again no fire.

Davew - it was a piston compression tester and I do know it reads 5 psi lower than actual; so add 5 psi to all of my readings. The three pulse measurements were made without a shrader valve and the combined pressure measurement was made with the shrader installed in the gauge.

Davew - I thought a bad or stuck ISC also but when running and idlling cold or hot the ISC cycles properly. When you increase the engine RPM's with the throttle the ISC closes then when throttle closed it opens fully then settles the idle down.

Arghx - when the thing died rolling to a stop I did put in second and let out the clutch; it would not refire; acted like complete ignition shutdown... I'll try the push and pop clutch if I even try to run it again without knowing the root cause....

bajaman - the car has always run perfectly up to 125,000 miles when the coolant seals let go. I bought a rebuilt street ported motor and installed it. Other than new gaskets, hoses and set of turbochargers it is exactly as it was before.

 

^ So....it is using the same ECU that worked with the other engine?

 

crank angle sensors and harness ok? Also, if it's flooded you'll know it. the plugs will be black and probably soaked in gas.

 

This is a rebuild from me, and I will say the compression doesnt look right at all. This engine was built when I was sourcing out my builds before I built them myself.

I have seen some unfavorable info about the Cermet housings as of late and wont use them again in the future. It is strange you are seeing higher compression numbers when cold then hot, I would recommend compression testing again. You should be seeing over 110+ with cermet houings. I hate to say it but it sounds like the hot starting issue is related to low compression, however, it isnt common one will die while running, especially if you are seeing compression in the 80s. How many miles have you driven so far on the engine, how much much run time?

Ill shoot you a pm with my phone number so you can give me a call and we will get this figured out one way or the other.

 

Just spoke with Tom (ttmott) and we accomplished nothing We are both stumped, he fired up the car with me on the phone, let it warm up(190F), cut the car off and it fired right back up as quick as it would on a cold start

Talking with Tom, both times the car has cut off it has cut off immediately not struggling to stay running like is typical when a car shuts off with a blown engine/flooding. However, after letting it sit and cooling off it fired back up on the same spark plugs which leads one to believe it would be low compression.

Im at a loss on this, it is obvious the engine should be making more compression than what it is making, but the symptoms for the reason it cuts off on him doesnt point to a compression issue, especially with it restarting after warmed up in his shop. Even after sitting for a few minutes turned off to heat soak it still fired back up while I was on the phone.

I gave Tom an idea to test next time it cuts off on him which should let us know if it is indeed low compression.

Any input would be appreciated

 

[QUOTE=djseven;9700316]This is a rebuild from me, and I will say the compression doesnt look right at all. This engine was built when I was sourcing out my builds before I built them myself.
QUOTE]

First of all let me say this: I had no intention discussing the builder nor do I belive this is an issue for me or any other member to critique the engine build or who built it. I bought this motor from another member who couldn't afford to finish his project. David Jerome (djseven) stood up unexpectedly and said his warantee as the builder was good and transferrable to me; not many would even consider doing that - kudos to you David. And thanks for your continued help!

bajaman - Same ECU as before; no changes.

arghx - if the crank angle sensors were reversed or mis-wired I don't believe it would fire at all. The ECU would'nt be able to detect start of sequence (one sensor) and the rotor firing timing (the other sensor). Unless you know something to the contrary???
The Plugs do have carbon deposits but are not wet. The engine will fire up every time when cooled down; only takes a couple of crank revolutions and it fires up - same as always.

djseven - the numbers are higher when hot; just not by any significance. Here is how I took the readings:

• removed the leading plugs.
• removed the egi fuse
• removed the shrader valve from the 0-300 psig compression test gauge.
• held throttle open and cranked engine
• took cold readings from the front and back rotors.
• the needle bounced in a regular pattern at the same frequency for the front and back. The needle was bouncing consistently 0 to 60+ psi.
• reinstalled the test gauge shrader valve
• cranked engine as before to get a maximum reading.

As a clarification, the engine will start as normal when brought up to operating temperature in the garage and idling. I can turn it off and restart easily. The issue is after a drive and decelerating to a stop the engine quiting and will not restarting. There is obviously a heat soak difference.

 

I was wondering about an intermittent, heat related failure. It's kind of a longshot though. If the car just cranks and cranks with no spark, it could be CAS related. If it's flooding (and flooding is easy to confirm), that is indicative of an injector problem or low compression.

I think you should put the compression question aside for a second. Recreate the no-start situation--warm it up, take it for a drive, and try to get it to die on you in your driveway or a safe parking lot if possible. When the car doesn't start, remove a leading plug. Inspect for signs of flooding. Ground it to the strut tower to check for spark as you crank the motor over.

 

OK. Now I am really guessing...

Quote: arghx - "I was wondering about an intermittent, heat related failure..."

The fact that it will restart warm in the garage also leads me to suspect a couple of areas that would be more affected by running the engine with load than in the garage without load:
1) fuel-pump/fuel-filter/FPR/gas-cap-vacuum-relief issues (should show up as low fuel pressure, i.e., lack of fuel supply). The gas cap issue is easy to check - open the cap, listen for air being sucked in, and see if it will start.
2) Intermittent electrical connection open-circuit triggered by heat, probably on the top or RH side of the engine where most of the heat is present in on-the-road running - could also occur in the fuel-pump itself, or its wiring
3) Intermittent electrical connection open-circuit triggered by cool air flow, probably on the front or LH side of the engine where most cool airflow is present in on-the-road running
4) Anything else you can think of that would be present after running under load but not in the garage

Dave

 

ttmott,

One option would be to borrow a PFC locally for a week or two. When/if you have the problem, snap photos of the Commander sensor diag screens and post them up.

Outside of doing that, I would start checking/testing the various components to the Pressure Regulator Control system:

 

The pressure regulator control system is mostly there to prevent vapor lock, and vapor lock seems unlikely. It's not a big problem on any fuel injected Rx-7 really. And the FD uses side feed injectors, which further reduce the amount of vapor building up in the fuel system.

 

The system is listed in the troubeshooting section for his symptoms (stalling when idling after warmed up, not starting when warm). It may or may not be his issue, however it was not listed in what has been tested and verified to be working (at least not what I read).

 

I thought about the PRC also and it is also discussed in the FSM as potential to warm stalling. But no CEL codes and it shouldn't have a lot to do with a restart issue. Just to make sure; the hose to the PRC solenoid is from the angled hose fitting low on the LIM, right? It isn't crystal clear in the hose routing diag's but that's the only fitting left after all of the hoses are installed.....

I going to venture out again and try to recreate the stall / no restart. Then get it right back into the shop and run another compression check and spark check. I did notice that during the two stalls and no start times that the engine cranked much more "freely" lending creedence to djseven's concerns (ie loss of compression) due to heatsoak. But it is very weird that once it cools down restart is not an issue and even when hot in the shop after idling restart isn't an issue.

I have also moved and wiggled all of the wiring harnesses and connectors without effect.

Thought, the injectors were cleaned and flowed by RC; can injectors stick due to heat soak???
Another thought, any experience on coil or spark box failure due to heat soak??
Last thought, I am also going to take a look at the MOP tubes (I replaced them) to make sure they are filled with oil; no oil would lend a decrease in compression.
If I have to remove the UIM, everything is going to get checked out, again...

 

You don't necessarily get a CEL when a solenoid is not functioning properly. If it was that easy, half of the twin turbo sequential problems wouldn't exist. The PRC basically in effect based on fuel and coolant temperatures (thottle, etc) so it does have an effect on hot starts.

However, if your compression numbers are what's listed above, then it seems like you do have a compression problem which could be affected by a slightly malfunctioning PRC system.

 

the PRC system cuts vacuum to the fuel pressure regulator for hot starts if the fuel temperatures are very high. Otherwise it does nothing. It was first implemented on 84 models, but it was triggered by the air temperature sensor because there was no fuel temperature sensor on the FB.

 

My thoughts on the PRC system:

The PRC system also raises / lowers the fuel rail pressure proportional to boost / vacuum unless the PRC solenoid is on then the fuel regulator only senses atm. pressure. So if the solenoid is malfunctioning and the clutch is disengaged, and fuel temperature is greater than 176 deg F, and throttle position is less than 30%, and start signal is received the solenoid will not give atm pressure to the regulator raising pressure proportional to the difference between cranking vacuum and atm. If cranking vacuum is challenged as we think then the PRC solenoid will have little effect on fuel pressure change.

 

I'm not going to argue with the two of you on the PRC system.

Troubleshooting effectively is about eliminating what is not the problem to be able to isolate the problem areas and focus your efforts. I spend a lot of days troubleshooting millions of lines of programming code. What I have my team do is "verify" something is a not a problem rather than guessing it's not, just so they don't find out is a contributor later. If you test and eliminate what is working, you have smaller areas to isolate.

Do as you like, but I would at least test the components but if your compression is really that low then there are bigger issues. The PRC system has a role in the two areas which are described as the problem and is suggested to be tested in the Quick Diag guide. I don't care if you follow the guide or not, it's your car.

 

Check it anyway to cross it off the list. The point I was trying to make is that your time would be better spent checking other things first.

 

PRC checkout:

• ECM connector 4M indicates 12V when key is in ign position
• When 4M is grounded can hear PRC solenoid click
• Checked out PRC solenoid with vacuum pump and 12V when engine was assembled.
• This should validate the PRC system is OK.

Purge System checkout:

• Pulled vacuum on Purge solenoid and it held so the purge system is is not leaking.

Will drive it again this afternoon (as soon as I can get a chase car); if it quits again we will tow back to shop (5 minutes away) and take another set of compression readings and verify spark. Also will put some ATF in the combustion chamber to see if compression increases.