dgeesaman

iTrader: (7)

I started my troubleshooting in this thread, but since it's a different issue I'm starting new.

I am having trouble with bucking above 0psi. Sometimes it's at 2psi, sometimes it's at 8, always is enough to create a noticeable buck and drop in boost. At one point between bucks I saw the boost gauge read a 14psi spike!. Up to the point where it bucks, the car appears to be operating completely normally. I can drive it at low speed, but it's not safe or driveable on the highway or outside my neighborhood.

Forum searches suggest this could be ignition breakup. The FSM suggests (page F-178) it could be the secondary injectors, ignitor, ignition coil, double throttle, MAP, and some other stuff. I've tested my compression and all the FSM tests except the ones using an oscilloscope.

I already have on the way a set of RC-cleaned low mileage injectors that I will probably install next. Then if that doesn't fix it, I'll go yell at Zach Keller for blaming the injectors and start swapping a known-good leading coil and plug wires. (My coils have 62k, and my plug wires have 10k). Other possibilities include the ignitor and ignition coil harness (which should be the updated version since I have a 94). I also borrowed a timing gun - would timing issues only affect high load/rpm?

Please, any suggestions to narrow this down and avoid me throwing $$ and parts at the problem. I would prefer to stick with my existing injectors and use that money elsewhere.

Dave

dgeesaman

iTrader: (7)

Bump. I still can't find any info suggesting a decent way to determine whether the bucking is caused by injectors or ignition problems.

Dave

quicksilver_rx7

Dave, not sure what ECM you're using. But, if you've got the PFC you could monitor the injectors when the bucking starts.

Stock ECM: couldn't you splice into the injector wiring on the ECM side with a multi-meter, you and a friend go down the street and monitor it that way?

Just a guess. I'm not an electrician

Joe

sub-zero

check your grounds on the engine, also look into an ignition amp and new coils.

BobfisH

how old are your spark plugs?

my car did EXACTLY the same thing. I replaced the plugs, and it cured the problem. The plugs i replaced were 2k old.

I was getting bucking and lack of power when boosting. It would be ok if you kept the throttle low and very gradually introduced throttle, but as soon as you boosted a bit too much, it would buck, lose power and boost spike every now and then.

dgeesaman

iTrader: (7)

I have a stock ECU. I could set up such a thing, but I don't know that it would appear on my multimeter, since the ECU sends pulses of voltage to duty-cycle the injectors. If the injectors aren't getting the right signal, I think only an oscilloscope would detect it. In any case, I've already swapped ECUs. I'll swap them again, just to be sure, but if the injectors are misbehaving I firmly believe it's because the injectors themselves aren't opening and closing like they should.

I replaced the plugs yesterday with brand new ones. No change, although the ones in there (with about 5 miles on them) were rather gunked up.

I had another thought today - if I managed to get copper anti-seize on things, or contaminated the boots of the plug wires, they could be shorting out under heavy load. I will remove them and clean them thoroughly - what should I use to clean them?

I'll also check my grounds and re-inspect the harness.

Dave

BobfisH

hmm, i dont know then im afraid sir, this is beyond my expertise! Hopefully you can get it sorted...start with the basics though, check fuel pressure is correct, check your FPR is working (this could be the culprit) there is a guide on how to do that on rotormafia.

Next check your MAP sensor hose is connected ok and not split, vac test check valves, check vacuum tank holds vacuum and pressure tank holds pressure.

Next i guess would be to check all solenoids - may as well do this while you have the fuel rail off if your replacing injectiors. Check my guide at http://www.face2faces.co.uk/RX7/howto/ratsnest1.htm. You want page 2 for the solenoid tests.


Good luck!

BobfisH

grounds are also a good idea to check, and i have no idea what to use to clean plug wires. Take the car out at night, pop the bonnet and check your plug wires are not arcing out on the block too.

quicksilver_rx7

What's the story with your OMP (MOP)? Could it be in "Limp-home" mode? or limp-when-boosting-just-to-aggravate-Dave mode

Joe

BobfisH

lol@quicksilver.

Actually, have you tried doing an ECU reset? I replaced my thermostat the other day on my car, disconnected nothing electrical bar coolant sensor and i went out and car would misfire and buck the SECOND i boosted at all. Took it home, removed and re-attatched the battery terminals (just to be sure) and did an ECU reset and it was fine. ECU reset is done by removing earth terminal from battery and holding brake for 10 seconds.

Gadd

What I would do at this point is........

Check the crank angle senser as per the FSM inspect the wiring closely.

Inspect/replace the coil pack sub harness, there is a updated one avalible from Mazda

There is an old trick to check the plug wires for leakage, spray them with tap water and see if the problems get worse.

dgeesaman

iTrader: (7)

I was thinking about the coil harness, but I have a 94 and I think that means I already have the updated one.

The ECU has been reset several times, and it never posts any codes. But I will be swapping ECUs soon and I'll be sure to do that again.

I did inspect the CAS's indirectly, by measuring the resistance all the way from the ECU. They came out in spec, so I think the wiring should be fine. Don't have an oscilloscope to verify they're sending a perfect signal though.

Dunno about the OMP, but the FSM doesn't show it having any effect in the troubleshooting chart.

I will try the plug wires - I have a spare set on the way too.

Herblenny

iTrader: (13)

I'm assuming you are running seq. set up?
Does it happen on both primary and secondary?

dgeesaman

iTrader: (7)

I'm on all stock sequential setup.

I think it happens regardless on both primary and secondary - if I rev it easily to get past 4500 without bucking, and then punch it I it bucks. But mostly I was testing/experiencing the bucking at lower RPM. I was pretty much only driving in my neighborhood.

I really believe the issue is not turbo control, since it can happen at different rpms and boost levels, and since the boost level jumps around when it's bucking.

Dave

mad_7tist

good thing to do would be get a fuel pressure gague and hook it up and drive it. rule out fuel supply issues. let the car idle and get a spray bottle mist the coils and harness see if you get any arcing. not a 100% test but a good one and only takes 20 sec. grounds and general state of ignition components are all suspects as has been said

Eggman

I had the exact same issue happen to me a few weeks ago. I changed the plugs....no difference (although they were overdue for a change). It turned out the stock computer was the problem. I replaced with the PFC/Commander combo and it completely cured the issue.

dgeesaman

iTrader: (7)

Well, so far I have replaced:
leading coil
plugs (4 times)
plug wires
ECU (twice)
ignition coil harness

and I'm in the process of replacing the injectors. I'd be testing it again, but I f'd up and broke an OMP line, dammit. I put off installing this set of injectors since they were $250 and I would have preferred to completely rule out ignition as the source.

It seems to be fuel / lean problem, since it can happen at different RPMs and boost level (in fact, I made it stumble out in slight vacuum), and because the engine just goes silent for a second and catches again, without any bogging when it resumes. I suspect if it was dumping fuel and/or not igniting properly, it would bog a bit when it caught again. But I figure it won't be till Wed that I get the parts and reassemble this mess.

Dave

charliegt

I had a problem with bucking under high rpm boost, turned out to be the water thermosensor. Its a $30 part at autozone, and A LOT easier to replace than the injectors. Mine was causing me to run rich all the time, and didn't throw a code for a long time. Could be worth a shot.

-Charlie

potatochobit

iTrader: (1)

bad coil packs cause bucking, not just the harness.

austinsFD

sounds like fuel cut...maybe? or yeah the seq turbos

dgeesaman

iTrader: (7)

Interesting. I will be sure to check the resistance of the ECTS at the ECU.

dgeesaman

iTrader: (7)

I replaced the leading coil pack, no change.

Dave

dgeesaman

iTrader: (7)

Fuel cut is a response sent by the ECU as a result of going over 12psi. But I suspect it's a much worse kind of fuel problem - injectors sticking and not injecting fuel under heavy load. Secondaries, I'm guessing. Considering there is no protection against detonation in this case, it's awfully scary. I'll do a compression test when it's next convenient.

Dave

Kento

That would be my assumption as well. If it was just the ignition breaking up or cutting out, you'd have a backfire, bogging, or rich "burble" as the engine came back. Sorry if I didn't catch you stating this in this thread, but did you carefully check the wiring and connectors to the injectors, both primary and secondary? It could be a ground fault that occurs once voltage reaches a certain point.

dgeesaman

iTrader: (7)

Thanks for the feedback.

I did check the resistance of the injectors both individually and using the whole circuit (from the ECU plug to the main relay terminal) and it all looked good. However, that doesn't preclude arcing at higher voltages.

But since the duty cycle signal to the injectors is a frequency signal that doesn't change magnitude, I really doubt that is the issue.

Anyway, I'll report back when I get my new OMP lines and everything back together. If I had the money around, I'd install a whole new engine wiring harness, but I really don't now. The gf is starting a business in January and the dog needs a little surgery so the FD can wait if that turns out to be the problem.

Dave