On the way back from a road trip my car started up really rough (took some cranking to turn over and then would hardly idle with violent shaking). This happened earlier yesterday as well but after driving for a few minutes the problem cleared up, but this time it didnt. It feels like it's running on one rotor.

Problems
-hard cranking
-rough/no idle
-absolutely no power
-slow revving
-had to rev to 3k to get moving from a stop
-would not boost over .3 bar (even on the freeway flooring it in 4th or 5th, normally creeps)
-could not build boost at idle
-major backfire/afterburn on decel (before under high load, but now at idle also

Anyways I got the car home and checked for vaccuum leaks first. I found one vac line under the UIM coming from off the vac spider that had popped off. I had to pull the UIM and TB as one piece to reattach it. Replaced all the lines coming from the spider since they were kind of loose. Put it all back together hoping that was the problem but it is still the same.

The gasket on the UIM seemed good still since the engine was rebuilt about 15k miles ago so it was reused. I still think I hear a vac leak around the UIM but tried spraying carb cleaner around that whole area but the idle did not change at all. Also checked spark plugs.

Running out of ideas right now and could use some suggestions. It may be possible that I routed 1 or 2 of the lines of the vac spider to the wrong place but I dont think that would matter since they are all coming from the same source. Please correct me if I am wrong.

I am now waiting for my friend to bring over the compression tester so yea I'll have numbers soon.

 

crossed plug spark plug wires? get those sons of bitches on the right plug if they arent already. Do a compression check, if its normal replace the sparkplugs and wires, pull **** off your intake, remove the uim to lim, replace all intake gaskets including the BAC valve gasket, and any other gaskets there might be, and check for vac leaks or potential vac leaks. weee

 

i say, before you go to any great lengths to fix anything, do a compression test

 

Just did a compression test:
front rotor= 90-95 on all sides
rear rotor= 85-90 on all sides

The plugs wires are all in their correct places. When I pulled the plugs on the 2nd rotor they were soaked in gasoline and had very very small traces of oil. Replaced those and it fired up alot faster but still struggling to idle.

I am still thinking it is a vac leak as I think I hear some sucking sound. I doubt it is the any of the IM since I was having this problem before I pulled them.

Would it matter if the vac lines off the spider were routed incorrectly? I mean they all come from the same original vac source right?

 

remove emissions and everything :-D unless you need it

 

yes, it would matter when things are plugged into the wrong hole...
check for vacuum leaks using carb cleaners.

 

Sounds like one rotor isnt firing all the time, or not at all. This is usually due to compression loss, but you have eliminated that. Next check for spark on all 4 wires consistently (using a spark checker or timing light) and check/replace all 4 plugs (stockers gas/carbon foul easily). Finally, check to see that both primary fuel injectors are opening, securely plugged in, etc. I have even seen cases where the engine harness had a short in the injector leads, which burned out an injector driver in the ecu and stopped one injector from working.

ONe way or another, sounds like one of the rotors isnt getting what it needs.

 

how would you find/fix a short in the harness? That seems like it would be a bitch

 

already checked using carb cleaner several and no fluctuations in idle

RotaryRessurection- I'll try and check all those things. Thanks for the input.

bump

Could this be limp mode? After some closer inspection I saw a very small puddle of oil where that line from the vac spider popped off, close to the MOP lines. I checked the lines but didnt see any signs of damage to them.

Could my MOP be failing causing limp mode?

 

You'd get a constant CEL if you were in limp mode. Pull codes for the hell of it, though.

 

fouled plug.

 

^plugs were already changed out

Update:

Spark seems consistant and fuel appears to be getting to both rotors. Repeated compression test and numbers came out the same. Right now I am ohming out the coils to test the resistance.

Any other things to check out?

 

Here are the results of the resistance on the coils
Leading= 1.0
Trailing 1= 1.4
Trailing 2= 1.3

I checked the resistance on my neighbors NA and the results were the same except in the trailing they were 0.1 ohms lower on each.

I'm running out of things to check.

 

What method did you use to check your fuel delivery?

 

The coils should be reading below 1 ohm each...Hmmm...Is the meter zeroed nicely?

I don't think that would be causing your problem, though...

Have you read out the primary injectors' voltages at the ECU while (attempting) to drive her down the road? If you have a "hiccup" in the electrical side of things, you might be able to spot it then...

 

Not a very good one actually. There were traces of fuel on the sparks plugs when I pulled them, but that doesnt mean much does it.

According to the FSM it should be under 1 ohm for the coils but I double checked on my neighbors NA and it was the same. How do I zero out the meter? It is a DMM. I doubt that is the problem as well.

I couldnt find a procedure to check the injectors through the ECU though.

 

Look up the ECU pinouts in the FSM (section 4 for the 86-88 cars, don't know what it is for the S5's). When you find it, it should show a "picture" of every input to the ECU, and which pin is what...Put the pos meter lead on the primaries (one at a time), and the neg lead to ground...You should get 12 to 14 volts steady (depends on your alt voltage), then see the voltage dropping as the duty cycles rise during driving...If one acts differently than the other, you can start checking harness, injector, & ECU issues...

 

Thanks Wayne

Does this have to be tested while the car is under load or will it be evident as the car is idling since is struggles to idle?

 

As long as the injectors are opening (or trying to open if they're stuck), the higher the revs, the bigger the voltage drop...You can really see it under load, but the driveway tests should work for now, as you just want to see if the injectors circuits are working as they should...

 

bump.... you fix it yet?

 

Nope not yet but I did check the voltages to the injectors from the ECU.

Pinouts:
3Z= rear secondary injector= 12-13 volts
3Y= rear primary injector= 0 volts
3X= front secondary injector= 12-13 volts
3W= front primary injector =12 volts

So I guess I have found the problem. Now the next step is to pull the UIM and check the injector harness?

 

No, if youre getting zero at the ecu, it must be a dead injector driver. IN the ecu. Still, I'd check and possibly rewire that one injector circuit...I had to do this once. IF it is an issue in the harness, it could come back, and it could kill the next ecu. I had this happen once, and I killed 3 ecu's before I got smart enough to just run my own 2 damned wires from the ecu to the injector instead of searching/repairing/testing and killing ecu's in the meantime.

 

Kevin, you'll be getting 12v there even if the ECU is dead-remember, that 12 is coming FROM the main relay, through the injector, TO the ECU. Even with the plug on the ECU disconnected, you'll still get 12v. The only time you won't get the 12v is when the ECU gives the circuit a ground (what you're calling the driver).

ilike2eatricers- remove the plug from the ECU, and get the harness fixes (or run new wires, like Kevin said). DON'T reconnect the plug until you get 12v on the bad pin, just in case there's a little short somewhere (I think you just have an open, though, probably the injector connector, or something close to there)

 

Thanks for the input guys. The way Kevin is describing it, it sounds like such a rare occurrance.

So I should be getting 12v at the 4 injector pins with the car in the ON position and can check those pins rather than it plugged into the ECU. So I should trace the wire from the injector to the harness going to the ECU searching for a opening in the wire or just run new wires altogether?

 

Most of the time I hear of a problem in the injector harness, it turns out to be at the connector, or just behind the "shell". Those wires get crammed all up under things when we connect them to the injectors, and eventually the heat & vibration get the best of them...

So, check the rear primary injector connector very closely. If you'd like, read the harness for resistance from the injector connector (make sure the ECU plug is disconnected) while "playing" with the connector & wiring near it. Use this method- run a wire to ground from the ECU pin the injector uses, then in the engine bay read the other end of the wire at the injector to ground (make sure you're on the right injector wire, since you obviously can't see the wire colors through the harness wrap, unless you cut some back). You should get something close to zero ohms- if not, play with it...If the meter jumps, then you'll know the defect is in the plug, or the immediate vicinity.

If you can't figure out where the open is, only then think about running new wiring...