Yes, this one has me stumped. A week of research, sifting through these forums until all hours, and I haven't found a solution that matches my symptoms.

Help from anyone would be greatly appreciated!

Basic problem (more detail below): Limp mode or fuel cut or boost problem that isn't solved with obvious or even many other possible solutions, and was caused by ONE specific event that should narrow it down greatly.

The car:
Car is a 1996 Series 7 RS JDM Rx7. Aside from Cat-back exhaust it is mechanically 100% original. NO engine mods whatsoever.

Background:
I tracked a recent coolant leak to the water pump housing gasket. I pulled a LOT of stuff out of my engine bay to get to it, including; air box and hoses, battery and tray, intercooler, alternator, air pump, filler neck, and finally the water pump and housing.
I replaced all gaskets and put everything back together in reverse order.

This solved my coolant leak, and I celebrated by driving cautiously for a few hours around town doing various errands including passing a mechanical inspection for my 'warrant of fitness'.

In the evening I went out again. After 10 minutes driving I could hear a slight whine/squeal and 20 seconds later boosted at probably 30-50% throttle in 3rd to very casually overtake a farm vehicle, and the lower connection of the S-pipe to the intercooler popped off with an audible 'pop/whoosh'. The whining sound was presumably the lower part of the pipe rubbing on the belts before popping off.

Immediate problem solved:
I immediately put the pipe back on, and while doing so realised I had forgotten to tighten the clamp ring onto the pipe when I put it back on after the repairs (stupid mistake, but not a big issue).
As I only had a screw driver and it was hard to get to, I couldn't tighten it as much as I'd like, so drove to my destination (about 5minutes) very cautiously - no boosting, but regular slow driving. All good on the way there, and all good leaving.
When I reached a main road and had to pull out into traffic, I had to accelerate - not hard at all, but slow gentle acceleration...

The real problem:
When I started to accelerate, the car lost power, bucked horribly and backfired. This immediately solved itself when I backed off the throttle. This has continued for a week now.
I can start the car perfectly. It idles prefectly. It revs perfectly in neutral up to about 5k RPM, then backfires until I let off the throttle. I can drive the car perfectly fine as long as I don't move the accelerator more than 10% or so. I have driven round the block fine, as long as I don't rev/boost.
My house is at the bottom of a steep driveway, and so the required throttle to get up the driveway means I can instantly tell nothing I am trying is working - as soon as I move with more than carpark effort, the car loses power, or bucks horribly and backfires.

What it isn't:

- It isn't the air hoses. I pulled off, checked, replaced and retightened all hoses to airbox, turbos, intercooler, etc. No issues.

- It isn't the repairs I made earlier. I re-did everything I did the first time, pulling almost everything out of the car, rechecking every plug, hose, etc for perfect cleanliness and connection, and tight clamps, etc. Every bolt is tightened, averthing is adjusted, the whole car is prefect.

- It isn't the TPS (Throttle Position Sensor). Despite not going anywhere near this in my work, the TPS can apparently cause these issues. I have checked with voltmeter using the correct procedure and adjusted. No joy.

- Unless I'm doing it wrong, there are no error codes. I have bridged the TEN and GND on the Diagnostics box turned power on - no lights flashing at all. I have tested using a multimeter and an LED tester and same result. I have disconnected the battery, stood on the brakes for 2min and reset the ECU. No joy.

- It isn't the grounds. I pulled, checked, cleaned and replaced all grounds. I even added three more - two from the battery to the gearbox and strut tower, one from the UIM (Upper Intake Manifold) to the firewall. No joy.

- Although I must admit I haven't chekced every vaccuum hose, I have checked everything that is visible peering into the engine with a flashlight, and the rats nest under the UIM. No hoses missing, popped off, or split that I can see, and all are new silicone hoses and in good condition.

- It isn't the hose that popped off the intercooler. This hose has a metal elbow around the lower bend, that protected it from the rubbing and the popping off. I have inspected it closely and it is all good.

- It isn't temperature related. I have tested warm, cold, restarting, etc, etc. No difference. Car runs prefectly and silky smooth under all conditions except normal accelleartion.

What it could be:
It could be one of 3 things (I think? - though if I really knew, I wouldn't be posting here!).

1. It is electrical. Something happened when the hose popped off that put the car into limp mode. Wierdly though, there are no error codes that I can tell, and it doesn't go out of limp mode after resetting the ECU. Most people's accounts of this tell of driving fine after resetting, then a few K's later it goes back into limp mode. Mine's in it immediately on start up.

2. It's boost related. There's a hose somewhere that looks fine, but is actually split and leaking, or there's a sensor that got fried or a turbo that died with an overload of boost or whatever when the hose popped off. But I would expect the car to drive without boost if this was the case, not jsut refuse to drive properly at all?

3. It's fuel related. For some reason ruel is being cut. This most likely relates to option 2 above, and an air pressure leak. When the car runs rich/lean the ECU is killing fuel?

Logical assumption:
This MUST be something to do with the intercooler hose coming off. My car is completely standard, and has run perfectly for years until this incident.
It would be extremely coincidental to be something unrelated.

Why I can't figure it out:
There is nothing that even vaguely relates to an intercooler hose coming off (especially on factory standard cars) that would cause this kind of problem - at least not that I could find with extremely in-depth searches and much reading.

I have only written this extensively in the interest of providing as many relevant details as possible, and finding an accurate solution.
Your help is greatly appreciated, and if you've actually read all this you are an absolute legend.

Awaiting helpful suggestions with eager anticipation!
Thanks in advance.
- Michael

 

If I was working on the car, I'd consider installing an Apex'i Power FC temporarily in order to troubleshoot the problem via the Commander.

Are you sure you routed the Oil Metering Pump lines and harness correctly and they haven't been damaged?

 

Hi, thanks very much for the ideas.

Unfortunately I don't have access to a PowerFC without buying one. I have considered the purchase on many occasions though, so maybe it's a good time to do it. This is a long term fix though as they need to be ordered from overseas here.

IIRC, the OMP lines are the two very thin clearish plastic lines that go to two ~10mm bolts immediately under the Water pump housing's location, along with the wiring (a thick bunch) that came up from there to a plug up above and to the right (when looking at the engine) of the pump behind the alternator?
If so, I'm fairly sure these were refitted correctly.

I will look up Oil Metering pump details today and double check if that's the problem.
If it is the OMP, then it would be limp mode right?
And how could the hose popping off affect the OMP lines? The belts weren't affected, nor anything near the OMP.
Hmm.. puzzling.

Thanks