khoney

Fellow Rotorites,
I've been working this problem for a while now, and have fixed some other idling problems along the way, but this one is getting the best of me. I don't want to try things at random (could get expensive), so here's a detailed description of the problem:

I am getting random VIOLENT hesitations at various RPMs and speeds (can happen in multiple gears). It seems to get worse with higher outdoor temps (90 and above). When it happens, I can hear rapid exhaust farts (a more technical term escapes me ). It is MUCH more violent than simply removing and reapplying throttle, in fact it can throw me forward in my seat, almost like stomping on the brakes. Of course, I immediately take my foot off the gas and cautiously reapply it. The problem occurs mostly between 2K and 3K RPM (max torque?)

I have:
1) Replaced the Bypass Air Solenoid Valve (only because I broke off a hose nipple while removing the intercooler).

2) Adjusted the throttle stop screw (was not making contact at all when at idle)

3) Readjusted the TPS (LED method)

4) Replaced spark plugs

The car had also had problems with wanting to die at idle and a bouncing idle. The above work seems to have fixed all that. It is now idling fine, still occasionally wants to die prior to a good warmup when the AC is turned on (lazy BAC?)

Anyway, here are my suspects:
1) Bad plug wires (never been replaced)

2) Clogged injector (I think I have a leaky one anyway, always need to pull the EGI fuse to do a hot start)

3) Misfiring?

4) Problem with TPS only when hot (looks OK when warm, no discontinuities in resistance, LEDS behave properly.

5) Bad ECU ground (would there be other symptoms I could check for???)

I was thinking of running an extension cable from the TPS check connector into the car so I can look at the LEDS when the hesitation occurs. I'm not sure though if that would isolate the TPS (i.e. could the LEDs also be affected by an ECU ground problem)?

It's got 140K miles, almost everything is original. Only fuel/systems emissions replacements are fuel filter and ABSV. I'm hoping to get some advice from the experts on what to check (and in which order!) What do you think is most likely to be the problem, and are there things not on the list that I should check? Thanks in advance for your help!

Everyone tells me "If you're having so many problems, why don't you just get a new car?". They just don't understand...

Kevin (would cry to see someone else drive it away...)

HAILERS

Sounds like your ignition is shorting out. Or your injectors(primary since its under 3800) wires are shorting out, coming loose etc. I''ve duplicated vilonet hesitation just as you describe it on a n/a by pulling the plugs on the secondary injectors and going for a ride. Rapid acceleration and reaching 3800 would throw me forward to the steering wheel. Seeing as its under 3800 maybe the primary wires have a bare spot that shorts somethimes. Another thing that caused a violent hesitation was when I replaced the vac hose to the boost (pressure, whatever) sensor on the r/h strut tower and did not put a orfice in the line. The car bucked violently until I put the original hose back. Darn, its hard to say where to begin on your car. Check the cas connector, coil wires seated etc, but you probably have done that. Reseat all the plugs b/t the ecu and the firewall, the plug on the airflow sensor etc. Ah shucks, check everything. Not much specific help here. Oh yes, I would not monitor the tps check connector. I'd monitor the output of the tps at the ecu, pin 2g.. Patch your digital meter to it and put the meter on the dash where the idiot lites go.

khoney

Well, tried new wires today, no help. HAILERS, you mentioned a hose to a pressure sensor needing an orifice. I busted off a hose today while trying to get my O2 sensor off, and it looked like it had plastic inside it. It goes from a rectangular box on the passenger-side strut tower to a barb under the BAC. Is this the one you're talking about? It was very brittle on the BAC end - I wonder if it had a crack in it. Does the orifice come with the hose when you order it? I'm also gonna get a grounding strap kit from somewhere. MIDNITE mentioned Pettit - anyone know if they have a web site?

HAILERS

Sounds like we are talking about the same thing. Its a boost sensor. Its black and rectangular. Probably has the numbers N326 on it. Has an electrical plug and a nipple for the vac hose that goes where you describe. Some people on this site call it a *pill*. If you do a search on this site and put pill in it, you can find the part number but there are a lot of posts to go thru. I found it several times. Sorry, I never took one out but from what I read you can just cut the old hose open and insert it. Evidently its just a little pill looking device with a hole in the middle. Every time I go to the wreck yard and I see one of these hose I get it. The ones I have have a stripe or dot yellow or blue. Irv, Keith's father mentioned in a recent post that he had the same problem when he did not put the pill in. At work right now(saturday?). When I get time I'll look up the part #. Did you say you still have the old line? Take it apart(razor blade) and try shoving the pill in the line somehow.

HAILERS

I just found a post you should read. Go to search, under key word put *boost pills*, then look for boost pills and the author rx7_turbo2. I KNOW you do not have a turbo. Look at the responses and you will come across one by Keith. Does his description match yours. I think so. It also describes the 87n/a that I own and left the pill out of. Some caution here. I have also seen posts from people that say they do not run with a pill and have NO problem. I'd rip the old line apart and insert the orfice in the new line.Then again it could be something else. Gotta start somewhere.

Keith

The pill is in the old hose under a white dot. It is a little white pipe with a small hole at one end and a smaller hole at the other end. I used a long finishing nail to shove it into my silicone replacement hose. Working fine.

Irv, Keith's dad

khoney

Thanks all for the pill info. Unfortunately I threw out the end I cut off because it was so brittle. It probably had the pill inside .

AND NOW ANOTHER EPISODE IN THE CONTINUING SAGA OF THE BUCKING REX:

I made a LED extension cable to bring the TPS test connector into the car so I could monitor the TPS LEDs while driving to see if the hesitation corresponded with a change in the LEDs. Well, I'm not totally sure what I'm supposed to be seeing, but most of the time when I had throttle applied, both LEDs were on. When off throttle, LED1 was on and LED2 was off. Sometimes with throttle applied, LED1 would be off and LED2 would be on. The '7 didn't seem to mind this condition. However, whenever the violent bucking occurred, the LEDS would be in their 'no throttle' state (LED1 on, LED2 off). I am positive that they changed state BEFORE I took my foot off the throttle to stop the bucking.

*** BTW, HAILERS, the DVM approach would be informative as well, but I feared rear-ending someone while trying to read the meter ***

I am also certain now that the problem gets worse with hotter outdoor temps. We had a cool front blow in today, and I didn't notice any problems with the car fully warmed up and the A/C on. On a real hot day, it typically happens at least a dozen times on my way home from work. So I guess if I don't solve this in another 6 weeks or so, I'll be resuming these posts in June of next year

Sooo, the $64 questions.

1) Does this mean it's definitely the TPS, or can an ECU grounding problem cause the LEDs to go bonkers as well?

2) Is the TPS at all serviceable (can I crack it open and check for things like cracked resistors?

3) Could the problem be on the ECU itself rather than the TPS? (I'm kinda doubting this one, because the ECU shouldn't get much hotter when its hot out).

BTW, the lack of a pill in the boost line doesn't seem to have worsened or improved anything. My boost sucks big time anyway (even with the primary cat empty), so maybe my sensor is shot anyway...

turborotarypower

it's funny you mention this violent bucking problem because about 5 months ago a guy e-mailed from my area asking if i could fix his tII which had the same problem. he told me went to a bunch of people and none of them could fix the car. well i take a look at the car and drive it to confirm the bucking which ws so bad you could actually hit your head on the steering wheel! anyways i look at it another day when i had more time to play with it. i get underneath the hood and rev the engine with the cruise control cable, once in awhile the engine will hesitate or hunt while i revved the engine.for some reason i brought a spare tII intake manifold along just in case.so after thinking of all the possibilities i decided to replace the tps. drove the car and the bucking has disappeared. i have spoke to the guy many times since and the problem has never came back!! so if i was you i would replace the tps first because the tps tells the computer when to idle and when to rev(increase injector pulse) if the the computer is getting false readings you will get these type of problems.

93fd 13.5@101mph bone stock with problems

87tII soon to be racing

NathanRX7

OK...I don't have a T2 and I don't know a whole lot about them, but all of this sounds A LOT like overboost fuel cut to me. Do the affected cars have FCDs?

Josepi

ACK!! Glad I found this one; I got a 91 TII that seems to be doing the same thing as described above, just at a smaller scale.

Did it start out small and get worse? Should I make adjusting TPS the first thing on my list? Replacing the TPS outright? Going to be putting in new plugs and checking the voltage to fuel pump today, figure i'll change the fuel filter while I am at it.

Mine is like this, at cruising 60 mph 2.6K in 5th, under WOT, no problem at all (unless I apply the throttle when the car is having its fit). When I am decel, no problem. It seems to surface most when I am nudging the throttle up gently.

Any Ideas??

Joe

ALTurbo2

fyi....
last week I cracked the vaccum hose with pill inside. I replaced it with some standard hose without putting the pill inside. My car was hesitating under boost, but not violently. I bought the "orifice" (pill) from mazda the other day and after inserting it, my hesitation disappeared. Best three dollars I ever spent!

khoney

UPDATE: Added another ground to the boost sensor last Friday. No help. Was getting ready to pull the injectors Saturday and send them in for cleaning when I read Big Woogie's post about the fuel intake filter being clogged. Pulled the fuel pump and cleaned the filter (didn't APPEAR to be that dirty, although after cleaning it I could hold it up to the sunlight and see light through it, whereas before I couldn't). Also replaced the crappy Autozone fuel filter with the OEM. I rechecked the thermowax and TPS. Went for a long drive out in the country, and it was OK. Came back home, put the bolts back on the intercooler, and went out again about 10 minutes later. Hesitation is back!

The car seems to run fine whenever I first drive it or if it's been sitting for a long time. I think the problem rears its ugly head after making a number of trips, as in getting back in the car after about 10 minutes and doing more city driving. I think my next step will be to monitor some of the ECU inputs while driving and see there are any hiccups. This is like having a second job! Hope you're still doing OK, Big Woogie.

HAILERS

Here is a site where RXSTER made a breakout plug for his ECU. I think I'd monitor the primary injectors and see if the voltage jumps up when this violent hesitation happens.

rhino37

Hey I had the same problem, so look at this thread.

https://www.rx7club.com/vforums/show...threadid=24896

If you have any ?'s e-mail me....


-Ryan