Fuel Cut/Hesitation Issue '88 T2
 

So, I have been trying to hunt down the reason for why I get an early fuel cut between 3500-4000 rpms. If I go just partial throttle, not even 1/4 throttle, it'll continue on up to 4k rpms and on. But if I give it 1/4 or more throttle it hits fuel cut around 3500-4000 rpms and falls on its face until I let off the gas.


It idle's perfect, rev's perfect sitting still all the way to redline, drives perfect under 3500 rpms.

I have a few idea's and have been doing tests with my DMM and other things but I just can not figure it out.

I figured it was the MAP sensor so I tested it.
The Black/White wire reads 12.2 volts
Brown/Red wire 2v at 3.9 in Hg
Brown/White wire 4.99v
Black wire is ground

I think I may have been doing the test incorrectly but it says to check pin D on the connecter with KOEO and the 3.9 inHg on the sensor.

I even hooked up an RB FCD to my map sensor just in case it was faulty, that way it would be bypassed. But it still has the same issue.


My TPS seems to be good as well. I hooked it up to my O-scope and it doesnt have any drop offs or spikes anywhere and I set it to 1k ohms at rest and it hits 4.4k ohms max/WOT.

My fuel injectors were just cleaned.
My fuel pump, fuel sock, fuel filter are all brand new.
New spark plugs, wires, coils are all good.
Timing is close but I have the wrong pulley so I cant set timing just yet.
Grounded the MAP sensor ground and pin C2 on the ECU which is the sensor ground.

Not sure what the problem could be..

Anybody have any idea's?

Thanks for any help

No idea's?

Im going to check out my resistor pack this weekend and see if it may be the problem.

Also going to fab up a test pipe to see if my original cat converter is clogged.

Sounds like the cat is clogged. ~4k is where instead of pulling hard it just chokes itself due to no exhaust flow.

The 2vdc with 3.9 inhg is lower than the FSM. Should have been on the output wire (BrR). Are you pretty sure of the 3.9 inhg being put on the sensor? Curious what you used to do that.

The resistor package can be checked out using a 87FSM. Pull it off the car. Measure the resistance b/t the middle pin to each of the other pins one at a time. Should be approx 6ohms on each.

Pin C2 on the ECU does not ring a bell with me.

Pin 2C, 2R, 3A, 3G are all spliced together and grounded on top of the rear rotor housing. They are the gnds for the ECU's internal electronics.

Pin 2A is the gnd to the boost/pressure sensor. It's also spliced to all the sensors on the engine.

I read a ALLDATA bulletin on the grounding of the boost/pressure sensor. It was to fix a problem with the gnd on the AFM. Since all the gnds for the sensors are spliced together and end up at 2A, I suppose they selected the boost/pressure sensor gnd wire because it was easier to access than the AFM plug wiring.

Maybe you have access to ALLDATA and can look it up? I have access no mo.

.

My fuel pump caused that same problem.

I used a snap-on hand vacuum pump for the vacuum on the sensor.

As for pin "C2" I meant 2C haha.
I regrounded the 2C wire as well as the ground on the Map sensor.
Colors were Brown/Black stripe if I remember correctly.

Yeah, alldata wasnt much help and had incorrect sensor voltage readings when compared to the factory service manual. That bulliten wasnt in with my TSB's for my '88 car, im guessing due to it not being an issue on the '88 and later model FC's. I'll have to look up an '87 or '86 car when I get back from my phase break from class.
As well as checking out the resistor pack today.

Thanks for the help everyone

On the RTEK Forum they had a problem with hesitation and the Digital Tuning people came out with a fix for it. https://www.rx7club.com/showthread.p...ght=hesitation

For me, I did the grounding of the ground wires for the ECU and that fixed mine. Some others also have had good results doing that.........others NOT. My cars are series four, turbo and non turbo, 1986/1987.

Yeah, I was looking at eventually getting a Stage 1.7 or 1.8 later on once i've got the majority of my car together and have the BNR stage 2 turbocharger.

Looks like I may be trying out the 1.5 to start with and see if it may help...

Thanks

Well, I gutted the main cat converter and checked out the resistor pack.
The car does run better with the gutted cat, and the resistor pack is good but the 3800 rpm wall is still there.


My AFM had 2.5 k ohms of resistance on one of the tests for the pins. Should have only been 200-600. Pins E2 and Vs

I have yet to drive it with the AFM I just put in it that checked out good according to my DMM.

Im going to be installing my wideband later tonight and see if its rich or lean during the 3800 rpm wall.


Any other idea's?
Im thinking that my secondaries are having some sort of an issue.

you said that the injectors were just cleaned did you make sure the clip were secured and did fall off

Im pretty sure the clips to the injectors are good and tight.
The previous owner installed new clips and I checked them myself and they seemed fine to me.

I just got my wideband installed about an hour ago and have some interesting results...

Idle: 11.1 - 12.1
Light throttle: 12's
1/4 throttle:13-14
More than 1/4 throttle: 13-15
Cruise:12-14

3800 rpms: 14-16 but could be due to the misfiring that occurs when it hit's the wall


Im going to pull the upper intake manifold and see what's going on with my secondary injectors. It's like they dont come on or there isnt enough fuel for them.
I'm also going to put my stock fuel pump back in and see if anything changes.

As soon as it hit's 3800 rpms it starts misfiring and backfiring. I tried to force my way through it earlier tonight and it would roughly continue up the rpm range but misfiring and backfiring and bucking the whole way until I changed gears. All the while the a/f ratio stayed around 14-16:1.

Well, I did a test that hailers suggested in another thread. Which was to pull the vacuum to the map sensor and cap it off to simulate a load on the engine and to see if the 3800 rpm problem is secondary injector related, and of course it is.

At exactly 3800 rpms sitting in the driveway the car bounces off of it like a rev limiter and it leans out everytime it hits, although the misfire could be causing the lean condition. So now im going to pull the UIM and check out my secondaries.

When I first put the injectors in I tried to compare the wires of the harness up to the FSM and haynes wiring diagrams but they just did not match. I thought I had hooked them up correctly, but maybe I didnt.

Would the car idle and drive fine up to 3800 rpms if I mis-matched the injector wiring?

I will find out later on tonight when I pull the UIM off and try to re-match the wiring to a diagram and see whats going on...

Thats either the injector pack or you got a bad injector in the secondarys. Most likely the pack same shit happened to my car

By pack do you mean the resistor pack?
I already checked it out according to the FSM and it checked out good.
I will swap it out for another one I have and see if anything changes.

If nothing changes then the UIM comes off tomorrow...

Well, I checked for voltage coming out of the resistor pack- a little over 12v

So I removed the UIM and checked out the wire colors to the injectors.
So far so good, everything is plugged in correctly according to the haynes wiring diagram. The FSM doesnt specify the colors all that well....

I tested for voltage, yep they all have a little over 12v.

Tested for continuity from the injector plug to the computer plug, yep they all have continuity and are the correct wires for the correct pins.

I re-checked the resistance of the injectors and they are all the correct low impedence injectors.


I am now stumped as to why my car runs like it does.
The wiring for the injectors is perfect yet my car acts like the secondaries dont kick on when they should.

Im going to try hailers' LED idea, except instead of having it on the injector plug im going to temporarily wire it into the harness from the ECU.
But, if the wiring is correct then they should be firing so I will save it as a last resort....

The needed sensors for making them work are working properly as well....

Im going to ground the remaining grounds that come from the ECU as well as build a better ground for the "3800 rpm hesitation" ground wires that are on the top of the block.

Possible bad injectors even though they were cleaned?

Any idea's hailers?

I checked the resistance at the ground wires for the injectors... only have .3 ohms of resistance in all 4 of them.

I made 2 grounds for the top of the block for the sensor grounds as well.

Still have the 3800 rpm wall....

Im going to simulate a load via the map sensor again and use my stethoscope and listen for clicking from the secondaries....
Then try an LED off the ground wires from the ECU....

If those things check out good then I have no idea....

Well, the exhaust leak makes it hard to hear for an injector clicking...

But my lead off of the secondary ground wire from the ECU lights up when it hits 3800 rpms and it bounces off of it until I let go of the gas.

I now have no idea what is wrong....

^ lead = LED

I dont know why I didnt think of this earlier...but I put a needle into each ground wire off of the ECU for the injectors and grounded it out intermittently with the ignition on and I heard clicking come from each injector which means theyre working fine for the most part.

So, possibly too much fuel because of my 255 walbro fuel pump?
The fuel, ignition, and externals are all stock for now so it's my only guess at the moment that it's too much fuel...

I am also looking for a '88 T2 main crank pulley to make sure that the pulley I have right now is the wrong one.
Anybody got one for $20 or so shipped?

Thanks

So did you ever figure this out? I'm having the same problems I know this is like a 6 yr old thread but hey it's worth a try

First thing to do is to explain your engine set up as it relates to any mods. Basically, this problem is a grounding issue or the secondary injectors are not operating properly because they are either clogged or have a poor connection via the injector plugs. Could also be a boost sensor, AFM or TPS issue.

Well Satch I won't thread jack as it is so old, you viewed and commented on my "exhaust issues maybe thread" but I found this thread and it better describes the exact same problems I have.