2ND Gen Problems

W

Weaver7

New member
Looking for some help with a low power situation that we have been fighting ALL year. It is evident that we have no power since I'm down and average of 5 seconds a lap at every track we have run this year. We have changed the following. New flowed/matched injectors.....new fuel pump new kill switch. Here is the real kicker Throttle position sensor in my opnion might be a factor in this whole equation. We installed a new one and set it using the fatory light and I also set it with an ohm meter and the resistance is within spec. HOWEVER when the car is idling and you lightly press the throttle linkage the engine surges 200 rmp's while it is surging the back bank is cutting in and out you can watch the EGT's have approxiamatley a 400 degree difference during this surge condition. If you run the engine about 3K it isn't evident.

We did a compression check with a standard compression guage today and the front bank is showing 90 psi the back bank is about 80 psi.....Any help would be greatly appreciated!
 
HHMM 5 seconds off and low compression, that sure sounds familiar

Take the schrader valve out of that compression gauge so you can watch the three pulses from each rotor. You'll probably need someone to crank the engine while you watch the gauge. Make sure the battery is strong, and the throttle is fully opened. Look for three even bounces on the needle. I bet you'll have one strong one, and two low ones on the back rotor.

That said,what caused this condition? Was it just getting old and tired, or did something cause a misfire/lean condition which hurt it? I'd hate to see a fresh engine get hurt by a bad harness, or something silly..
 
Tom
you might try and swap your tach pick up from your lead coil pack to the trailing coil pack.
and see if your tach still works properly.
we have run into this in the past, the engine cranks just fine, rev's fine on jack stands,
just kind of soft under load and won't get up to normal shift points.

won't hurt to try.
hope this helps
joe
 
Tom
you might try and swap your tach pick up from your lead coil pack to the trailing coil pack.
and see if your tach still works properly.
we have run into this in the past, the engine cranks just fine, rev's fine on jack stands,
just kind of soft under load and won't get up to normal shift points.

won't hurt to try.
hope this helps
joe
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Joe, on trailing coil where should we try pickup? Thanks Tom Weaver
 
The stock tach connection on an 86 is the trailing coil. Yellow wire with blue stripe. Pages 50:16 and 50:20 of the 86 FSM.
 
Just because you get a tach signal off a coil doesn't mean you're getting spark. Check to make sure the double throttle blades haven't fallen shut on you. Have had it happen to myself and have heard of it happening to others.

Other than that you have a tired engine. Low cranking compression really shouldn't dictate a huge power loss though. I've seen engines with abysmal compression numbers run pretty darn well at high revs. Has it always been a lame powertrain or has it just become so recently?
 
Chris I will check the plates good idea. I did do the old trick of checking with the timing light each wire and they all seem to be firing.....Is 90 PSI on a standard guage bad?? The back rotor was only registering 80 psi.
 
Saturdays Adventure :bash_1_: Moved the Tach pickup to the trailing Coil, found during the week that the header(RB) had a large crack in it and have had it repaired (back ordered) now in poking aroun under the hood up by the check TPS connector we found a knob that when turned seems to change the idle speed. Look in shop manual and it is called a variable resistor located next to a small box referred to as "Boost sensor" any ideas??????????????? :blink: T W :eclipsee_steering: Chris we do have the plates wired counter clock wise.
 
Saturdays Adventure :bash_1_: Moved the Tach pickup to the trailing Coil, found during the week that the header(RB) had a large crack in it and have had it repaired (back ordered) now in poking aroun under the hood up by the check TPS connector we found a knob that when turned seems to change the idle speed. Look in shop manual and it is called a variable resistor located next to a small box referred to as "Boost sensor" any ideas??????????????? :blink: T W :eclipsee_steering: Chris we do have the plates wired counter clock wise.
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The pot is a variable resistor that changes idle mixture. That's all it does. The boost sensor is simply Mazda speak for a MAP sensor. The ECU mainly monitors the AFM but the MAP sensor plays into the whole scheme of things too. You can unplug it and the car will still run fine.
 
As its66 said above, the rear rotor should have 3 even pulses. A standard gauge would hold the highest pulse pressure of the three thus giving a "false" reading . You are looking for the one rotor face (or more)that has the bad seals. The rear rotor is often the first to go on a bad engine. Mazda has a special rotary specific compression tool that charts each individual rotor pulse. With the plugs out you can hear the compression pulses alternating (front rear, front rear, front rear). Maybe you just have a sticking seal. Try the atf trick. (automatic trans fluid). This will sometimes free up the seal. Works great for deflooding an engine also.
 
. Try the atf trick. (automatic trans fluid). This will sometimes free up the seal. Works great for deflooding an engine also. [/b]
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And it works great for killing mosquitos in 3 Texas sized counties.

Double check that compression. The Mazda guage is best (John Weisberg in Rochester has one) but you can eyeball it as well. As suggested above, remove the schradrer valve and the plugs (1 per rotor) and crank away.
If the compression has an even pattern, but is low, then there is general wear on the rotor. If the pattern is high, low, low, high, low, low, etc, then an apex seal is suspect. And if the pattern is high, high, low, high, high, low, then a side seal is the issue.

Once you know the mechanical condition of the engine you can continue to troubleshoot.
 
what was it Tom.
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Well first let me say we did all the suggestions of help offered above and compression seemed good (within Range) Friday at Watkins Glen Bill was setting the tps and we were doing routinue stuff. Our one crew member is In Topeka with F500 guy (we are diverse) anyhow all year loong on occasion the exhaust would have a VERY acrid smell now being from the old days of pre emission controls etc etc that was an indication of a Vacumn leak. On the plenum is a pipe that had been capped with a hose and bolt (keep in mind we had used the WD-40 trick to find leaks to no avail) anyhow We discovered it was leaking around base pulled it off and on the under side the hose was cracked. Quick trip to NAPA for the Large Vacumn cap (never have the right size) and we were ready to try again. Now I'm not certain but I think the secondaries depend on at least some vacumn assistance to open & remain open before the engine would pull to about 7200 and then go flat now it pulls strong all the way up to ( oops trade secret). Someone let me know if I'm at least a little correct on my theory on how the secondaries work? We went out Sunday am on wets fog and overnight rain and managed a 38th spot to start as Bill had little traction on the wets. In the race he moved from 38 to 19th (by passing) never thought a 19th would bring such relief. Everything we did will help and again thanks to all as every bit helped.. :D Tom weaver
 
Well first let me say we did all the suggestions of help offered above and compression seemed good (within Range) Friday at Watkins Glen Bill was setting the tps and we were doing routinue stuff. Our one crew member is In Topeka with F500 guy (we are diverse) anyhow all year loong on occasion the exhaust would have a VERY acrid smell now being from the old days of pre emission controls etc etc that was an indication of a Vacumn leak. On the plenum is a pipe that had been capped with a hose and bolt (keep in mind we had used the WD-40 trick to find leaks to no avail) anyhow We discovered it was leaking around base pulled it off and on the under side the hose was cracked. Quick trip to NAPA for the Large Vacumn cap (never have the right size) and we were ready to try again. Now I'm not certain but I think the secondaries depend on at least some vacumn assistance to open & remain open before the engine would pull to about 7200 and then go flat now it pulls strong all the way up to ( oops trade secret). Someone let me know if I'm at least a little correct on my theory on how the secondaries work? We went out Sunday am on wets fog and overnight rain and managed a 38th spot to start as Bill had little traction on the wets. In the race he moved from 38 to 19th (by passing) never thought a 19th would bring such relief. Everything we did will help and again thanks to all as every bit helped.. :D Tom weaver
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Sorry but the secondary sleeves do not work off of vaccum. They work off pressure supplied by either pre-cat exhaust back pressure on an S4 or the air pump on an S5. If you are running a proper exhaust you should not be making enough back pressure to activate the sleeves...problem. If you have enough pressure to activate the sleeves you're cheating yourself out of some power. And I've never seen a racer leave the air pump on...problem. The sleeves provide no benefit to an IT can and the restriction they create for top end flow is real. Remove them along with the actuators and try again.
 
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