professionalpyroman

Gentlemen,

I'm having problems with my car, Series 5 Turbo, RB streetport, BNR stage 2 turbo, everything else stock. Had the thing running like a dream, but this past week it started to lack any sort of power and I have to rev the thing to about 4k to start going at a stoplight and it doesn't build boost as it should. It also doesn't want to start without pushing the gas pedal.

Again, it idles fine and steady, not high or low. TPS sensor is within spec (and brand new).

I checked for vacuum and pressure leaks and the intake system is tight as a drum, no leaks. I also checked it with vacuum and pressure guages. When I rev the engine, the guage on the dash stays stuck down until you put the engine under load like going up-hill, and then it ticks it a little bit. It doesn't even come up to zero when the you just turn the key on.

I did check the map sensor, and it is not putting out the proper signaling voltages according to the FSM. I also checked the wiring back to the ECU and even checked the ECU for burnt traces. Those all came back fine.

First question: Would a bad MAP sensor cause this lack of power and crappy performance?

Second question: Replacing the stock map sensor would cost a boatload of money. I am planning on upgrading to a Haltech ecu in the future and was wondering if there was an alternative sensor I could use to replace the stock one? Haltech offers 1-3 bar map sensors that are 3 wire, I just don't know if the signal voltages are appropriate. If you guys could give me some guidance I'd appreciate it.

Matt

clokker

iTrader: (2)

Have you pulled codes yet?
If the MAP sensor is outputting faulty data, the ECU should be bitching about it.

professionalpyroman

Yup. Throws a #13 code - pressure sensor. 5v and ground signals are good and clean. signal is all over the place.

I'm checking with you guys to make sure because the cheapest I have found a new s5 pressure sensor is $340 at atkins rotary. I've bought used sensors before and regretted it. I might be getting a new ecu in the next year or so and I want to make sure that I have to replace the stock one as is to run it, or if I can upgrade the sensor not have to buy another one when I get the new ecu.

Appreciate the help

clokker

iTrader: (2)

I recently faced the same dilemma and went with used.
There doesn't seem to be a suitable replacement for stock...I know the GM sensor that Haltech likes won't work with a stock ECU.

professionalpyroman

Thank you for the info!

That was what I was worried about. I don't have enough knowledge yet to figure out an IC adapter. I'll just order a stock one and if I need to upgrade later, I can.

Appreciate the help

j9fd3s

iTrader: (3)

its very rare for these to fail, so a used one should be ok.

also you may want to make sure that the connector pins are clean and tight

Black Knight RX7 FC3S

iTrader: (7)

if you apply 100mmhg (3.9inhg) on the pressure sensor and it comes within 1.9-2.1v at the sensor AND at the ecu wire, the sensor is fine. If its not within the voltage range, you need a new sensor.

professionalpyroman

just got a brand new boost sensor from Atkins. Plugged it in and ECU code went away. However, now it is still not registering the right air pressure. At atmospheric, with the hose unhooked, it is still giving me an incorrect voltage.

These are the readings key on, hose unplugged, measured to ground. FSM specs from page F2-78 ecu pinout.

+4.95v on the + side (FSM spec of 4.5-5.5v)
0v on the ground side (FSM spec 0 again)
2.27v directly from the signal pin of the sensor that goes to ecu input 2H. (FSM spec 3.4-3.6 v)
I don't have a good means to measure vacuum. I can try to rig something tomorrow. Again, brand new sensor. Factory boost gauge on dash was working won't even budge when you turn the car on.

Vacuum leaks have been eliminated starting from lower intake and working back out using an air compressor. Also checked wiring connections from sensor to ecu. Again, no measurable resistances, good continuity.

Gonna see what happens when I put 3v of signal to sensor line. Should cause needle to jump at least a little.

Any new ideas, please let me know. This gremlin can be defeated, I just need help from folks like you guys.

satch

iTrader: (1)

You're looking at the wrong pin out, as there is one for the turbo and one for the NA. Pin 3R states it's for turbo boost, which would obviously be for the turbo model, and the readings for the boost sensor are 2.2 to 2.5 volts on that particular pin out and not the 3+ volts you'll find for the NA sensor pin out.

professionalpyroman

Copy that. Thank you for the correction

satch

iTrader: (1)

It was an easy mistake to make for they don't explicitly highlight which is which so you have to look at the pin out list and see which one has info for a turbo and then you know which one is which.

KompressorLOgic

iTrader: (6)

street port, and an upgraded turbo, and no ecu/injector/ fuel pump mods?

have you done a compression test?
"but this past week it started to lack any sort of power and I have to rev the thing to about 4k to start going at a stoplight and it doesn't build boost as it should. It also doesn't want to start without pushing the gas pedal."
^ this sounds like the description of a blown motor...

or perhaps post a video if it idling and reving up?

professionalpyroman

I've got a video for you, and some pictures. Video link: Not a youtuber, so don't expect MCM quality.


Good news!: Replacing the pressure sensor did improve the performance of the car. The ECU seems to like it, and the thing doesn't dog at stop lights. Took it around the block and it moves around far better than it did.

Idle is smooth, starting from a stop is fine, gets up to speed quickly.

Car makes appropriate boost 5-7psi as indicated by cheapo boost gauge shown in video, plenty of power. I realize that's a little low, but its my daily driver and until I get a new ecu and stuff, I'm not running it hard. My wife would murder me if I did and shelled the thing. I did upgrade my secondary injectors to RC ENG 750s so that it wouldn't lean out if it took on a little extra boost, and replaced the fuel pump.

Current ongoing issues...: Found a small vacuum leak in one of the oil injectors at the seam where the nipple is pressed in the top of it. Can't replace it for a while because of cost, might JB WELD or braze. Wish they'd use better materials for those.

Dash boost gauge is a dirty liar. Do you guys know where the connectors are for it so I can check continuity, etc? Might also have something burnt out on the back of the gauge cluster that I'd need to resolder too. Ideas welcome.

Darn squealy water pump. This one is a month old. Same thing happened to the old one. New belt too.

Battery charge light keeps coming on, even though battery is healthy at 12.57v. Again, ideas welcome.

MjhRotor

iTrader: (1)

I noticed in your video you don't have an air pump and are only running one belt on your alternator. If you eliminate the air pump and run a mechanical fan you should use a dual belt alternator pulley or serpentine belt kit like Atkins uses to prevent water pump slip from lack of belt wrap.

There's to much load on the water pump pulley and not enough belt wrap without the air pump belt especially if the mechanical fan is still present.

Edit: Check alternator output when the battery light is on its likely a bad alternator not charging. The battery light indicates a lack of alternator charging not battery health. Also a slipping belt on the alternator could cause a lack of charging.

professionalpyroman

Yup. Air pump and split air solenoids got busted in a wreck so I eliminated them. I had a buddy turn down a dual pulley for me so I'm going to pick it up tomorrow.

The alternator is brand new, but I found the problem thanks to your suggestion. The wiring in the plug on the back had broken where it joins with the wiring harness. I cut out that plug and soldered the wires in place, then heatshrunk and wrapped them.

Now that most everything is playing nice, I need to figure out how signal is not getting to my boost gauge. The dial was working. There could be a wire that broke in the wiring harness in the engine bay. That's where I hit during the wreck. I have good continuity to the ECU. I guess my next step is to try to find the junction where the signal goes to the boost gauge. I've been looking at the wiring diagrams but this one is hard to pin down. It's probably one wire I would guess since the gauge cluster likely shares a ground.

Again, you guys are awesome and I appreciate the help. I've been trying to restore this thing for almost 14 years now, but I'm getting really close. This has been my daily driver for years, all through college and grad school. I'm trying to get everything as close to stock as I can, but if there are improvements to be made for peace of mind/ easy performance/ drivability, I'm all for it. Most upgrades so far, aside from the porting have been because of parts availability. But that was also because I didn't know what the inside of the engine was like. I also got Goopy Apex seals and better corner seals as well.

I'm trying to make sure I have all the creature features too. I replaced the transistor in the fan, and cleaned out the fan slider switches. If you haven't done that, the results are great. Tons of ice cold air conditioning! Just got cruise control working too.

Matt

professionalpyroman

Found and fixed gauge issue. All is well. Thanks guys

satch

iTrader: (1)

And the gauge issue ended up being.....?

RXSpeed16

iTrader: (41)

How did those got damaged in a wreck? They're bolted to the block!

professionalpyroman

Sorry for the delay, I was out of town for a while.

The solution to the gauge not working was that a small amount of corrosion built up on the contact points on the back of the gauge cluster. I guess 30 years will build up some corrosion. I checked the voltage at the main connector behind the gauge cluster and it was matching the sensor voltage. So I took out the screws, shined those and the contact points up with a toothbrush and put it back together... very carefully. I got a look at the wire that constitutes the gauges, and its really really tiny.

The reason the split air stuff and air pump were broke was that a few years ago I was flat broke and thought $50 tires were a heck of a deal. Headed to a friend's for supper and the right rear popped on me on a good hot summer day and I found the ditch and impacted on the front right side. Totaled the car. I stripped it of every part and bolt I could and bought this frame. The previous car I had was an 89 TII - S5. I found this 88 turbo rolling frame that a kid had tried to LS swap and boned up. I put all my S5 stuff, harness, interior, engine and drive train in it and its almost complete.

Only things I have yet to put in are:
Fog lights - still have s4 bumper cover so I'll have to get creative on placement.
Automatic seatbelts - Gotta figure out if they'll fit on those pillars
ABS - need to get wheel gears and sensors, master cylinder, portioning valve. Can make my own lines if need be. This will probably get completed last, if ever. I have the parts for the lights and seat belts, but I can't afford these parts right now.

clokker

iTrader: (2)

No, they won't.
I've converted two S5 chassis from auto to manual belts- it takes longer and involves much more than I'd thought- but can't imagine trying the reverse.