87 TII runs rich, lacks power above 3K. Tried everything
 

Okay the basics. 1987 Turbo II, S5 housings and rotors, s4 everything else. Hybrid turbo rtek 1.5, 550cc primarys, 720cc secondaries, racing beat catback, and a aftermarket downpipe I believe. Also an innovative AFM

So I bought this car a year ago with all the mods on it. It ran great except the infamous 3200 rpm stutter. The previous owner told me about adding a ground to the boost sensor, I read aaroncake's write up about the grounds and tested them all. They were all good so I went a head and added another ground in parellel to the boost sensor. Big mistake. The car has never been the same. I took it around the block and as soon as I hit boost/secondaries it was like I hit a wall, it started to boost and then fell on its face, hard. So I turned around, removed the ground and its still acting up. ugh why did I bother. Now when I start hitting boost, around the same time the secondaries turn on, the car runs way too rich, like 9:1 on the AFM and lacks power really bad. It will continue to accelerate and the rpms will climb but its not right, the car is unhappy and seems to have a bit of a stutter continuously once its into the secondaries. I can cruise in the higher rpms and it seems okay until I try to accelerate, even the slightest bit. I have barely driven it since this issue because I don't want to hurt it. :(

I have been working on this single issue for months with no avail. I even took it to a supposed rotary specialist and he said wrong injectors...which isn't the case because it ran totally fine with those injectors before. I even swapped in some brand new 720cc secondaries to be sure the ones I had weren't leaking. Before I took it to the shop I checked all my grounds, inspected my plugs/wires and swapped in known good coils. tested my ECT At the ecu from a cold start and made sure it dropped accordingly as the car warmed up. Checked my crank angle sensor, TPS, swapped in another boost sensor, swapped in a different ecu(stock TII without the rtek1.5), hooked up a scope to my primary and secondary injectors at the ecu, all have good patterns (comparing primarys to secondaries they look the same so I figure this is good?) I've even tried yelling at it. I've read that unplugging the tps and blocking off the tube to the boost sensor simulates load and it doesn't act up when I do this. Just free reving in neutral. So this is my last resort, posting a jumbled thread on the rx7 club. Is there something I am missing? Do you have any suggestions for things I should check/recheck? And kind of Tests I can do? Or even a guy to take it to near Vancouver Canada? I've read a lot of posts trying to find answers but nothings seems to help. Any guru's have anything happen that sounds similar? Any help is appreciated!

W/o reading your whole story you need to go back to the ground you added to the boost sensor and recheck which wire you added the ground to. There are 4 wires to choose from. W/key to on the Black/White wire has 12 volts. The Brown/White wire will have 5 volts w/key to on. This leaves two wires left and one of them is Brown/Red and it should output about 2.5 volts w/key to on. The last wire is the ground wire. I bring this up because some people end up grounding the wrong wire. Secondly, for a stock ECU 550cc injectors are used on a turbo. Unless you have a non stock ECU you should not be using the larger secondary injectors even if they worked fine before.

satch is on the right track. wonder if u fried a wire or something for the boost sensor. Does your factory boost gauge still work??


as satch says running the 720s with the 1.5 will make the car run a lot richer than intended when the secondarys do kick on.

at a 50% duty cycle when they kick on it would result in about 15% more fuel going in the ecu thinks

for example say your A/F were 11.5:1 before they kick in, they would drop down to 9.9:1 at the transition which is too rich

you would probably get a stumble everytime due to the size being wrong....

Thanks for the input guys! I rechecked and the wire is the brown with a black stripe on the boost sensor. This is the ground wire from what I have read and I checked it with a multimeter before I added the ground. I did a voltage drop test on it recently and it was good, cant remember what the reading was anymore tho. Can recheck tomorrow. Factory boost gauge is working

I also put the 550cc injectors back in today, car runs better, not nearly as rich, but my issue still exists. It almost feels like detonation but I am not sure. It lacks power and struggles to accelerate once the secondaries come on. Is it possible that they are firing at the wrong time? Or could the ignition system have been affected by the ground issue? Although it doesn't seem ignition related I'm just out of ideas. It runs great at the lower rpms and boosts hard until the secondaries kick in.

If the voltage of the 4 boost wires checks out okay then your issue could be TPS related. The linkage which rests against the TPS separates completely at about 3000 rpm which is where you notice an issue. When the linkage separates from the TPS the output reading from the TPS should stay constant as the engine speed increases. When the linkage separates the voltage reading of the Green/Red wire of the TPS should measure about 4.5 volts w/key to on. The sweep range of the TPS when the engine is fully warmed is 1 volt at idle and 4.5 volts at max so see if this is what you have or not.

Also, check the ohm reading of your secondaries as you cannot mix and match injectors that are low and high impedance. Early 87's had low impedance injectors while late 87's had high impedance.

Do you still have the double throttle plates on the throttle body? When they stop working, they default closed. I had this issue about 20 years ago and just about lost my mind trying to figure it out.

So my multi meter was at work but I grabbed it today, this is what I got

Boost sensor key on:
black/white: 11.7 V
Brown/white: 5.07V
Brown/red: 2.42V
Brown/Black 0.13V

Seems okay to me, I checked the range on the brown/red wire with a pressure/vaccuum tester attached to the boost sensor and it was good with no dead spots.

TPS Key on engine off but warm:
Green/red: 1.02V
Brown/white: 5.1V
Black: 0.2V

Green/ red sweep: 1.02V-4.81V
Is 4.8V too high?

I did these tests underhood, Ill be rechecking at the pcm this weekend.

And yes it has the double throttle still, I'm having trouble finding into on the T2 double throttle. How can I test/inspect this? Whats there to know about them?

When you check the tps, was that after at least a 20 minute drive?

Have you done a boost leak test on the car?

I warmed the car up and took it for about a 10 minute drive around my neighbourhood. Car is uninsured so I didn't want to drive it too much last night

No I haven't, what's a good way to test? The car starts to boost fine and then starts to crap out when the secondaries fire. Doesn't sound like it's leaking boost, I've inspected the hoses for cracks and they're all in good shape.

Wire the double throttle plates open to see what happens. If the cars runs well, you'll know where the problem. I'd do this before checking anything else.

The double throttle plate should just default to open if you cap off the vacuum line. I don't see the need to wire open.

Except they don't default open. They default closed. They default open on the FD. Mine did that and it took a couple of weeks to figure it out.

exact same symptoms happened to me when the injector resistor pack failed. would check the connector first.

Well I have a s4 t2 tb here on my work bench that defaults to closed . My s5 t2 I just installed tonight the secondary plates default to open when no vac applied

That's interesting. Mine was an S4.

Okay so here's a follow up. I never got it running properly after adding and removing the parallel ground I added on the correct wire of the boost sensor. Very very weird it caused an issue since adding a ground in parallel with other grounds shouldn't cause any issues. I believe it was an issue with my stock engine harness, a short inside the harness somewhere. I had a microtec LT-9C installed with 4 LS coils and 4 new injectors and a few new sensors along with a custom built harness. Oh and a rebuild with a big street port. Car runs frickin awesome now. Putting down 280 whp with the stock intercooler and no water meth.

Thanks for following up.

no problem. Better late than never I suppose haha

Who did the rebuild and the custom harness? I wouldn't know them, I was just curious.

Forcefed Racing in Abbotsford Canada. Check them out they do a lot of cool stuff. The harness they built is really tidy and has all sealed connectors.