hey guys. i gutted my precat and silencer the other day on my 88 base, and now, when i floor it, it gives me these wierd, short hesitaions. i thought i might be a vaccum leak bc i did just change the vaccum line to silicone, but i checked them and it still hesitates. i'm planning on doing the whole "rats nest" mod soon to eliminate the possibility of it being a vaccum leak. i'm also planning on ditching the air pump bc i no longer have any cats whatso ever. what could the hesitaions be?

 

whats the rat nest mod?

 

Rats nest mod is removing all the emissions.

 

what kind of hesitations? certain rpms? high rpms only? anywhere as long as you are floored? fuel cutout (pump/filter)? or tps? bad plugs? bad coolant temp sensor? plug your o2 sensor back in? There's a range of things. If it's only when you floor it, I'd assume it's a tps as during 3/4 throttle you may still drag it out to redline only slower. but I'm thinking you may just need new plugs if it's at like 6k rpms or something.

I had to change my plugs every month otherwise I would see an impact in performance from 6k-7.8k I had a coolant temp sensor go out on me and i would get sparatic hesitations from 4-7.8k tps could make it just horrible (my g/f's zcar got the sensor wet at one point and the car wouldn't rev past 2.5k)

 

Do you still have the main cat on?

 

the main cat is out.

i just put new plugs and wires in it.

and it happens around 4000 rpm.
it only does it when its floored and i'm begining to think that its the fuel filter bc i looked at it the other day and it looks like its never been changed. i'll let you know if a new fuel filter does the trick.

 

if your car is an na you have to have backpressure from cat to open fifth and sixth ports actuator unless you have an electronic actuator now

 

You screwed your car

I suggest buying racing beats system now. Or find a main cat at the junkyard and plug it back up. The final option is to have the smog pump open the the 5th & 6th actuators.

 

What are you talking about. Hesitations don't mean his car is screwed! Rotaries don't need a whole lot of back pressure, just enough to keep the un burnt fuel in the chambers from overlapping and ... (over your head) never mind.

vato2000taco you're right. He does need some way to operate the AUX ports. Maybe he does still have the tube because the Main cat is still there and maybe it isn't who who's? Although I never noticed a hesitation on one of my customer's car when his AUX ports weren't operating, just a drop in higher RPM power. It is a bitch to get the Air pump to operate the AUX ports because right now he still has the Emissions hooked up, plus you need a air solenoid and RPM switch to open a valve that in turn opens the AUX ports. No where on a 88 NA is there a built in ECU switch that turns on at about 4k-5k RPM's that he could tie into that could operate the AUX ports. Now if it was a S5 then this would be a completely different story...

What do you have for the back end of the exhaust? I'm guessing you have gutted the first cat and pre-silencer and have left the main cat alone and from there it goes to the Y pipe then to stock mufflers... That right there is enough to run a NA Rotary just fine. Something else is up. Sometimes the AUX actuators get kinda stick over the years and require a little more pressure to work. And since you have lowered you B- pressure a little one of the actuators may not be opening or not enough causing an un even intake pattern into the engine causing the Hesitation.

When all else fails check the basics again like the TPS etc. and really change the Fuel filter. If it looks old it probably is. Your secondary Injectors open at 3200 RPM's and they could be not getting enough fuel flow to them.

Good luck and keep us informed with your progress.

 

thanks for all the help. its really not a bad hesitation, but i love my car and would love to have it fixed.

my exhaust set up.
- gutted silencer, precat, and main cat (still have the tube that goes from the main cat the engine tho)
- back to dual HKS mufflers (fart cannons....they're pretty much nothing)

i'm really good with cars and electronics, so if you can tell me more about that switch (pros and cons) to open the actuators that would be great.

- where can i get an electronic actuator?

i just orderd a new UIM gasket so i can do the rats nest mod to get rid of all the emmisions...will this help?
i was planning on removing the air pump a little further down the road as well....good idea with my current situation?

 

You are going to loose performance if you just forget about them.
It's much better just to have them open at the right rpm. They use exhaust backpressure from the main cat to function so once its gone they no work.
So it's time to buy a rpm switch and a walmart tire airpump to activate them.
Someone said something about a electronic actuator?plz fill me in

If you remove the airpump your going to need
A. pineapple racing alternator relocation kit(I have one myself)
or
b. Dual alternator belt pulley( a bunch of companies make them)

Because the pulley system is balanced and once you take something like the airpump off then you will get slippage at different rpm and slippage is not good.

 

Just throwing in my 2 cents.

If you are interrested in getting your ports working right and removing all your emissions. I suggest getting the presilencer/down pipe kit from Racing Beat. It replaces all the cats and is a direct bolt up to the stock manifold to the stock y pipe. The pre-silencer has a built in pick up tube that is used to run the AUX ports. That solves any exaust probelms you might be having and partialy fixes the aux ports problem. The kit costs 320 plus shipping. Not bad at all for something that will last the life of the car.

Next up, while you are getting a uim gasket. Get the full intake set. While you are taking out all the emissions crap take off the lower intake, the manifold that bolts to the block. This will give you access the the aux ports. Pull em and clean em up. This is will make sure your ports are fully working.

Another plus to getting the RB kit. Removing all the emissions includes ripping the air pump, acv, and egr. You will need block off plates for the ACV and EGR. The RB kit comes with the block off plates and gaskets for em. Another reason the $320 is well spent.

How ever you plan to do it all, I bid you good luck

 

Search for 3800 rpm hesitation.

They open at 3,688, not 3,200.

 

Back pressure does not "keep unburnt fuel in the chambers from overlapping", at least in a N.A. engine, where the intake is not pressurized. Low/No back pressure means that more of the exhaust gets out easier, meaning more exhaust leaving the chamber and LESS overlapping into the next intake chamber. Please back up your statements before saying it is "over our heads."

Sorry for jacking the thread, unless I missed it, no one said to check any wiring. The stock 20 year old harness can cause several problems. Inconsistent voltage to ECU, fuel pump, and the list goes on. Just another thing to check.

Nick

 

how would i hook up this rpm switch?

"rpm switch and a walmart tireair pump!?"

where can i get an rpm switch?

 

I had the same hesitiation. It was 100% exhaust system related.

remove your gutted cat and no more hesitation.

your gutted cat is acting like my expansion chamber. just remove the cat and its all good.

 

Explain to me how a tube is causing hesitations?

Ugh, ignore this person please. It has nothing to do with exhaust or 5/6th ports (according to other people).

Search for 3800 rpm hesitation. Fix it, done.

 

the main cat?

do i remove the tube from the engine to the main cat too??

....by the way glhs0867. U ROCK if this works

 

............................................

 

My5ABaby - srry bro....we must have posted at the same times.

but wouldnt removing the cat housing create a little more back pressure bc instead of going into a huge housing, it has to go through a smaller diameter tube?

and i did search for hesitaions.....i'm going to check my grounds when i get out of work bc i remember no hooking up the one that goes to the bell housing bc the clip was brok and rusty, but it never did it until i removed the cats.

 

Don't worry about it.

Backpressure, to my knowledge, isn't going to cause a spontaneous hesitation, especially at ~3800rpm, the classic hesitation point due to bad grounds. I'm far from an expert on fluid dynamics, but I would assume pressure moves at a constant rate, going up or down. I don't see how at a certain rpm there could be a large enough change to cause a hesitation. I'm not even sure how (if?) backpressure could cause a hesitation.

 

You have no electrical problems.

Its the cat loading up with raw gas and the 02 is reading this, and cause odd hesitations.

can you sometimes drive through that rpm range and get no hesistation?

if so, you descibred exactly what happened to me. cut the cat off and replace with either new cat or a straight pipe to replace the missing cat.

try it and see. I check everything under the sun and it was my exhaust.

I really have no problem, if others think its crazy, I really don't give 2 ***** about these tools.

It was my problem.. thats all and it sounds like yours also..

 

glhs0867.....sounds like my prob.....it is pretty random and hardly ever does it. i'm deff trying ur idea first.....seeing as its cheap and easy...although, grounds have been known to create other problems tho so i'll do that as well.....thanks a lot for the info. i'll post on the result of both ideas.

 

1. The O2 sensor basically reads rich or lean. It does this a bajillion times. So how would one change from lean to rich or rich to lean cause a hesitation at one point, but not at any others?

2. Even with the 3800 rpm hesitation you can still get normal days. Before I fixed it some days it would do it, some pulls it would do it, and some it wouldn't.

 

Its actualy quite simple realy. Exhaust is being pushed out of the rotor housing into a tube of such a size. This gas has a density and an associated pressure to it. The gas moves through the tube staying relatively constant because more gas is constantly being added by the engine. As the gas hit the open chamber it expands and loses pressure. After the gas fills the chamber it gets pushed back into a tube of the same size it was in before.

What happens then? It get recompressed to fit in the tube. This causes something along the lines of a backlash wave, small yes, back toward the engine. This is back pressure, exactly what is used to drive the aux ports on a S4 except through a pick up tube that doesnt have gas moving against the wave.

In restrictive exhaust systems like the stock cats, you get lots of back pressure. What does this back pressure do? Less potential engine power which is exactly why people get rid of their cats. That is why a gutted cat can cause a weak hessitation vs a straight pipe or presilencer.