cbrock

iTrader: (1)

From the title, I'm dealing with a 3500-3800 rpm hesitation. At around 3500 the car sputters non-stop until you dump throttle or push deeper. At 3800 I get a dip in response but pulls through. Then sometimes below 4k it seems to take longer to build boost almost like timing is being pulled or something is way off. Car is an 88 with 49k orig miles on the clock.

Thus far I've got all braided fuel line, aeromotive filter and FPR with a walbro pump. No additional damper other than what might be provided by the FPR. I also regrounded everything...though I never replaced the main lug on the rear rotor...might do that tonight

I unplugged the TPS sensor...car would barely idle but when I did get it off the line it still had the break up at 3400-3800. Plugged it in...better idle still has the break up. Unplugged the pressure sensor (wire not the source line) and it seemed better. I checked it out some time ago and it seemed to be working as I watched the voltage sweep as I applied a vac from a hand pump.

So I'm starting to doubt that it's ignition break up but more of a fuel starvation like the secondaries not coming online. As when I plugged the FPR (pressure went up a bit due to lack of vac) and it seemed a little bit better.

I might fart with the TPS a little more, try some pressure sensor tricks and put a new lug on the main factory ground on the motor. Then EVERY ground should be good. Then I unplugged the FPR vac source so it doesn't rise 1:1 and up the base pressure until it goes away....if it goes away.

Any point to running a ground strap to the AFM now that it's just floating in space with the new TID and filter?

TRRAPLN

I have the same problem after a rebuild. I get a stumble when the secondaries come on. I can alter the activation point of the secondaries via my Rtek and the stumble is at the same place.
Pressure at idle is 36-38 psi increases to 42ish when I give it gas, but I don't know what its doing at 3600-3800 rpm.
I just tried more grounds, but no change. I now am suspecting my used FD fuel pump or the TPS.
If it was the TPS, the bogging would be at the same place and not change with the secondary staging rpm.

Did you have any luck fixing your problem?

cbrock

iTrader: (1)

hmm..not yet. But I did pickup a cheap analog volt meter to look for dead spots in the TPS (a digital meter might not pick it up) and it is perfect. I am now going to tap into the knock sensor, 02, computer diagnostics and pressure sensor feed so I can monitor the signals when the car hesitates.

I do know that mine started off as a slight stuble and I realised I had my pressure set to high (now idles at 28psi and jumps to 36-38 when it gets back to "0" and then 1:1 after that) when I lowered the pressure it got worse, but should have been more like stock at that point.

I'm going to try raising the pressure until it goes away. But I suspect that would only be a bandaid as something is causing the seconaries to delay.

TRRAPLN

Today I change fuel pumps from the FD back to the FC just to see if it makes a difference. I'll also check resistor redidtance and voltage to the pump. Pump has been rewired. After that I might focus more on the TPS and my dead spot. See my other post showing my TPS plot.

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/gurus-comments-tps-plot-574714/

If our cars see a stumble via a TPS dead spot, do they go to shut down? Whenever I get the stumble, It is hard to drive through it and my graphs show the TPS goes to idle even if I keep my foot on the pedal.

Never the less, the stumble only happens at the secondary on point so TPS is still suspect of being OK. I need a good used TPS to swap in place.

Hambino60

dude i just posted something like this about 7 post before you. i'm haveing that same problem with my TII. Although i get to about 5000 then i get the heavy hesitation.
Does your fuel pump sound like it's working too hard? i used to have that but i found out that i had some lines crossed that was f ing up my pressure.
I still have the hesitation , cleaned out the 2ndaries - they were dirty as hell and clogged up the butt. NOw i'm wondering if secondaries can burn out or stop working.

TRRAPLN

My secondaries are brand new RC Engineering. My Rtek says the are getting a signal so I now begin to wonder about the wires goin to the secondaries.
Soon, we will have traced the whole system. No solutions on my end yet.

cbrock

iTrader: (1)

that seems to be the joy of this issue. Well, actually what I believe to be two seperate issues. There is the classic 3800rpm stuble that everyone says add grounds, check this, check that and I think that can be traced to poor grounds.

There also seems to be a handful of people that have a hesitation start at 3400-3500rpm. Mine for example bogged at 3500, picked back up and quickly bogged again at 3800 and then floor you in the seat as it pulls to redline.

Really it seems everyone is having the same exact problem which should be able to be tracked down to one particular fault.

I don't know what the common link is yet. Mine seemed to start after I put in the FMIC. Got wrose when I was able to fiddle with base fuel pressure via the aeromotive FPR.

Seems to be control related as it is a very specific spot (RPM and TPS) above and below the car seems to run normal. Bad injectors, wires, plugs or fuel filter you would suspect poor performance through out the RPM range.

Either way, this needs to be carefully documented once a solution is found as I believe it will aid many a 7 owners.

As a side note, you said your TPS drops to idle readings when yours hesitates? But it checks out fine when you measure using the resistance method? That sounds like something funky in the ECU itself. Perhaps another cold solder issue that is just starting to appear. I've noticed the number of these complaints becoming higher over the past 5 years I've been poking around this board.

TRRAPLN

I had the stumble intermittently before I rebuilt the engine. I now have the engine running but can't get past the stumble. I seemed to get worse after all my mods. But I have the ground wire kit, relocated battery to the rear. Complete new rewire on the power/alternator harness, high output alternator. My voltage gauge reads 13.5 + most of the time. Plus I found some ground issues in the 5th gear switch and fixed that so my 5th gear an neutral switch are back working. The Rtek is great for feed back via their diagnosis screen.
I even ran my jumper cables to the engine compartment ground lug from the battery ground to see if that made a difference. No change.
As for cold solder joints, I don't know where to look or repair. More input on that topic would be helpful.
My fuel pump voltage and resistance check out, at least at idle.
I'm swapping pumps just to eliminate an option.

cbrock

iTrader: (1)

There are no known cold solders on the ecu itself...but that doesn't mean it can't happen. I might have a slight intake manifold leak on mine. I'll hook up so I can log, collect as much data as I can and then fix the manifold and check for improvements.

wargoblin

I'm having this issue too. I got my engine rebuilt and redid my engine harness. I've added extra grounds to the boost sensor and injector harness. I've been having this problem for months, however I think I found a possible culpret for it. I have to do more trail and error testing. But I have reason to believe its ground issues with the dash/ chasis harness. When I have my Stereo and Air OFF, it seems to hesitate much less. I haven't realized this because I usually run with my Air on. And now thats its cooler and I don't use it, I'm noticing this. I'm going to be adding some extra grounds for the chassis harness and update you guys.