Power loss around 4500-5000 rpm

[GEN 3 SHO FAN]

I have a little trouble with my 96.

When the motor goes near 4500-5000 rpm, he have a big loss of power with hesitations but no misfires (8 new plugs, 4 news rears coils and no code for that, new TPS). I tought first it was the trans going away but it's shift correctly in others rpm ranges.

I'm wondering if it's related to the fact that we change the gas tank last summer (too much rust on it) and the dealer doesn't sell me the good one (needs 3 holes on the top) and sold me a 2 holes (97+). Sadly, we remark it only when all was unbolt... We put the new one, retreiving the sensor on the 3rd hole. That gives me rapidely the code P0453 (Evaporative Emissions Control System Pressure Sensor High Input). Seems to do nothing on road as it is a emission code.

Is the regulation of the fuel pressure in the tank by the PCM can have negative effects of that importance ? When near at WOT the pressure in the tank must draw substantialy and if the car think the pressure is high and opens the valve all the time (creating a vacuum to the intake maybe), can this have a negative effect on the pump trying to send fuel to motor ?

Thanks for your help,

 

[stephen newberg]

Well, if its not a misfire, that is electrical, that does mainly leave fuel. Simple things first. When was the last time you changed the fuel filter? If it is starting to get plugged, as flow pressure on it increases, it will not let enough through to meet demand, and could cause your problem.

pax, smn

 

[GEN 3 SHO FAN]

Thanks for your reply Stephen, I ask the same thing to some gen II guys and they never answer me... (even if one seems to have the same trouble).

All the filters were changed last summer (air, fuel, trans and cabin too). Gas is always premium on it.

There is a chance that the fuel pump is slowly going away ? Or the last owner replace the fuel pump by one for SLO which is weaker...

Thanks for yours lights,

 

[stephen newberg]

Well, the most strain on the fuel pump does occur at WOT and at higher RPM, so it might be the pump going. Before we totally give up on electrical though, its worth remembering that the coils when they are intermittent very frequently do not set codes. I notice that you mention the 4 rear coils are new. Does that mean the 4 front ones are old?

pax, smn

 

[GEN 3 SHO FAN]

I tryed four new coil on front bank I changed the cam position sensor in the same time yesterday but the same thing happens. (I will replace the crank position sensor too soon.)

It's seems to be heat related because yesterday the temp was high here (86) and the trouble came sooner around 3500 rpm.

I rode somewhere when it's the trans going away it create heat and the motor feel it and may do mistakes trying to delaying the sparks (some kind of motor desynchronization). However, I watch the heat needle and it's stay always in the first half of normal zone.

 

[GEN 3 SHO FAN]

I changed the crank position sensor which was very dirty (oil). We clean all around and put the new one.

How a one bolt job can take 2 hours ? This ************* decided to broke in the crank (this was the original one)... %$?/&!

Oh, and the bug still there.

 

[stephen newberg]

Hmm. Difficult. Of course, if you shifted the 4 new coils back and forth between banks and the problem remained, it is always possible that the problem is with one of the new ones. Though most people seem to report that these coil packs from China do fine (mine have), there have also been a couple of reports of getting a set and one or more of them being dead on arrival and needing to be replaced.

But the ambient temperature figuring into it would seem to argue against coils and instead point at a sensor problem of some sort. Have you been having any starting hesitation? If so, cleaning or replacing the intake air sensor might be the next thing to try.

pax, smn

 

[SHOdded]

Maybe even heat shield the harness/coils on the firewall side?

 

[stephen newberg]

Never hurts. Some people do it, though I admit I have not bothered. I checked to make sure that there were no obvious areas where contact would occur and past that have ignored it. If that were the problem, I do not think you would be finding it changing with ambient air temperature. Assuming a relation there, we are almost certainly looking at some sort of sensor problem. The car does check intake air temperatures, and modifies all sorts of things on that basis, such as fuel metering, advance, etc., so I think looking at that air intake sensor and seeing if there are any problems in the area of the air box might be your next thing worth checking. But at this point I am guessing, I am afraid.

pax, smn

 

[GEN 3 SHO FAN]

At the moment, the motor have 8 news coils : 4 forward chinese and 4 Alanis deals ones on rear bank (I don't mess with them). When I did this change, I also put protection on rear wiring harness (long tie rapped black plastic shell). But when I did this the wiring was already sticked on the head and a little toasted... I need a screwdriver to get it. I retreived the 2 metal bracket and give them a new shape to be between the motor and the wiring, not keep the wiring against the head. (!?)

Ok, I will check the air intake sensor. I rode also that there is a wiring going into the trans (somewhere on it) can have problem with too much heat.

 

[1BAD91]

It could be your secondaries are stuck closed. Mine was doin the same thing, when I started driving my 98 again. Then after a few days, I went WOT and it of course bogged when it hit 4500 then all the sudden took off and I heard the secondaries open. Every once in a while it does it, if it sits for a while.

 

[stephen newberg]

I suppose that is possible. The simplest solution to find out is to wire them open. If that solves the problem, then just make the wire open permanent. Easy to do and works fine.

pax, smn

 

[GEN 3 SHO FAN]

Ok, I will check that too. I wired open them one time but I had some trans problems. Can they stop working when hot ? (I never rode about a thing like that...) Yesterday at night, I never heard the note famous note... broken cable ? Will see that.

I checked the Intake air sensor but it seems to be a part the air box... It's possible to retreive it ? I unpluged the switch for check up, nothing wrong. Can it need a clean up ? (I don't have a oil filter in the box.)

There is also a switch on the the top of the trans C186 (?), not sure about the number, which is going to the pressure solenoid in the trans which can suffer from heat... someone know what am talking about ? I have not found it yet.

 

[stephen newberg]

The secondaries are not associated with the transmission, so wiring them open and leaving it that way will not cause other problems. Many of us, me included, have had the secondaries wired open or completely removed for years now. Well, over a decade, even.

Yes, the IAC is in the air box. It can be removed for cleaning or replacement. It tends to damage easily, so some people just replace it rather than trying to clean it. It very definitely does get dirty and start creating problems with engine starts and running just using a normal air filter setup.

pax, smn

 

[GEN 3 SHO FAN]

I watched my secondary this morning and the cable is good but it seems that they are not working... (no code, based on the sound) It is possible that they are working sometime and sometime not before scrapping ? I will try to open them by hand.

 

[stephen newberg]

Yes, and it is possible that the cable moves but the flaps do not, depending on where things are broken. Wire back the actuator itself, taking the IRMC box and cable entirely out of the equation.

pax, smn

 

[GEN 3 SHO FAN]

I rode somewhere that IMRC does something based on dyno measurements. I have 2 IMRC from SLO (paranoid reflex) maybe I can repair it...? I would like to keep the car in it's original shape.

 

[stephen newberg]

There have been a couple of serious test series done on the IMRC and in fact though it works and is meaningful on the V6 or the Gen I & II, on the Gen III is ends up actually doing nothing at all. In fact, it somewhat disrupts air flow simply by being there at all, and some of our more serious members have gone so far as to remove the butterflies and fair in their attachment points to smooth the intake. If you want to keep it going, you likely need to take the box apart and see if the gears inside are striped. That is the most common failure. Next most common is that the wire abrades through. And last most common is that the butterflies stick.

Personally, I left the box and wire in place and just wired the actuation lever all the way open. Works fine.

pax, smn

 

[GEN 3 SHO FAN]

According to the sound, it seems they doesn't open at low speed but they open at higher speed... (?) I opened the small box, all the gears are mint. When I will have time, I will rewire them open just to test.

Is it possible that some still stuck close when the others open up ?

It is possible to unplug the IAT sensor from the box or I have to change the box to change this sensor ?

 

[stephen newberg]

The normal operation of the butterflies is that they are closed at low RPM and open up at higher RPM, so yours might be working fine, or intermittently. It causes no harm to have them open all the time, regardless of RPM, so that is why it is common to just wire the actuator lever open.

On mine the IAC sensor can be unplugged and removed, but I cannot swear that is so for all years.

pax, smn