87cncnu

Recently had the car in the shop with an idling problem (it wouldn't). Had the intake and turbo gaskets replace, and the idle improved considerably.

However, driving home, I noticed a significant hesitation at about 3500 RPM, and the boost would refuse to increase (and maybe drop a little) from where it happend to be, when the hesitation occured. The car will normally pull up to about 8lb. boost, but if it happened to be at 4 lb. when the car hesitated, it would go no further up.

Just to complicate things, occationally..it works just fine!

Engine is a relatively fresh street port, with a manual boost controller.

Any thoughts??

solve_et_coagula

Sounds a little like t.p.s.

87cncnu

I've always had tps problems at lower rpm's. Besides, I read that the tps is basically out ot the loop by 3000 rpm (don't ask me to explain that). Anyway, not sure why the tps would act up at the same time I had work done.

I'm guessing something got cut/hit/diconnected when the boys were in there working on the turbo or LIM gaskets.

The question is....what might have happened while they were working, that would cause the symptoms described?

misterstyx69

iTrader: (142)

I don't understand how people can get work done at a shop,have problem with the car and not take it back to the shop.
If it was Ok before they got at it,Take it back.

87cncnu

Well...I really didn't want to clutter up my question with a lot of ancillary information that doesn't pertain to the problem at hand. 'Course, if you think that somehow might add to the ability of my fellow RX7 Club members to offer advise...then fair enough.

So I picked up the car a week ago Thursday. Got on the 401 and noticed the issue descibed previously. Couldn't return to the shop as it was late afternoon, and its quite some distance away (no ride arranged). Went back the next afternoon (was occupied in the morning; doctor's appointment; nothing serious). While it seemed OK on the highway, it again displayed the above noted issues after I got on city streets. Drove past the shop to a little used road and wound the car up through the gears...same problem. While driving back to the shop, the problem went away!!!! Tried to make the problem re-occure at the shop...no luck(aint it always the way). Did a cursory look around at likely culprits with no luck. Drove home with it working fine. Fired it up last Sunday to head to Mosport...problem is back and hasn't gone away (unfortunately, Mosport was a washout for me).

Meanwhile, mechanic is away in California for 10 days! Fully intend to take it back on his return, but I though I'd see if my fellow club members might have some insight that I could be armed with when returning to the shop! Thought that was at least in part, the purpose of this forum!

So you are right, you didn't understand why I hadn't taken it back to the shop!
Now you do. Hope that was helpful.
Now, any advice on my problem?

MazdaMike02

iTrader: (4)

TPS needs to be adjusted after fixing vacuum leaks. Do you have a wideband? What's the AFRs when it hesitates? And what else does it do? Does it buck? Or backfire? Or does it just sit and then go past the hesitation?

87cncnu

Thanks Mike

Best of my knowledge, there was no TPS adjustment done, so I'll look at that.
No wideband, but I do have one of those circular LED air/fuel guages. Idle is lean - constant throttle is just about mid guage - throttle application pushes it into the rich zone. All normal for this car.

The hesitation is mild at low throttle, and significat at full throttle. More like a "buck". No backfire.

At the hesitation, the fuel/air slams over to full lean, takes a second or so to recover, then moves into it 'normal' range.

Car continues to accellerate afterward, but the boost stays where it was when the hesitation occured (assuming I keep my foot in it). So, if I have, say, 2lb boost when it hesitates, I get (largely) no more than that even if I keep the throttle open. If I have 6lb., it stays at 6. Car feels like its struggling to accelerate....almost like it was running very very lean....but the A/F guage says its normal.

MazdaMike02

iTrader: (4)

Anytime you fix almost anything to do with the engine the TPS should be checked. The narrowband air fuel ratio gauges are pretty much useless. Just tell you that the o2 sensor is working and if its in closed loop.

Your issue sounds exactly like a TPS issue. Adjust it per the FSM or use a digital multi meter. Specs are listed in the FSM. I would do that first and go from there.

Also I would get rid of the narrowband gauge and buy a wideband. Get an Innovate one, they're relatively well priced and work very well. Its very important to know the AFRs. On a rotary lean=boom, no forgiveness. Detonation=Boom as well.

sctRota

iTrader: (2)

OK OK I KNOW THE PROBLEM!!! (I think :P) I meant to make a thread about my hesitation but I might as well explain it here.

A few weeks ago, I built a new custom ported motor for my 88 convertible as I believed it was time to get a little faster out there.
The motor I used as my donor was from an 86 s4 na that come out of a running car.
When I finshed installing my new motor, I decided to use the 86 harness with the resistor pack as I came with the car and my 88 harness would not plug into the water temp, primary and secondary injectors. So I used the 86 harness and everything was plugged in. I used the 86 ecu, all grounds were put on, and started up perfectly...
HOWEVER.... Reading my apexi and tach, I would get hesitation when accelerating past 60-70% of my throttle. I instantly thought the ignition was shot or a lack of fuel (FD pump btw) was happening, but remember everything was working perfectly before... So I spent the day removing the harness and putting back on the 88 harness and now it works perfect! If you want, drop by my shop and ill see if its the same. This was a problem that I thought I would never solve but it did infact work out! If I was able to find my wiring diagrams for the fc's, you would see that the grounds from and towards the ecu are in fact in different places for the 86, 87 and 88. The TPS is normally at fault in many cases, but I have a feeling that this is not the TPS this time. I used the donor TPS, my original TPS and a random TPS from a box and all did not solve the issue. I highly recommend you check the harness, I would post a pic of the differences on the 86,87,88 harness' but there are all at the shop and wont have time till next week to find them again.

I would also like to put out, that this is solution also works for T2's as I solved a friend's hesitation as well


EDIT: Now that the redbull is cooling off, I think this may deff me a ground issue... Get them to check all grounds and the boost sensor.