Quick Slow Down Question

Hi Guys, I did search the forum prior to starting this thread and it did provide me with some guidance, but I just wanted to confirm that merely running straight pipes on a 2.7 motronic system shouldn't light up the SD (5-8) bulb. I will check the thermocouple as well as the ECU for tight connections and clean them out as well. The car has been running extremely well since its last alternator rebuild (constant 14.3 V thank you) and just started acting up a couple of nights ago. Intermittent slow down and then a power up to normal as I made my way home. I'm going to be putting my high-flow cats back on to pass emissions testing shortly, but just want to make sure that I'm on the right track.

Thanks to all of you for being just a keyboard stroke away when problems arise.

Cheers, Henry

 

They don't on my 2.7. In fact I used them to prove (to Ferrari) that the Exhaust CU was fubar.

 

How are your coolant temps? After full warm up, how far does your coolant gauge go down while on a steady cruise on a cool night?

 

I'm between 170-190. Just installed a new thermostat two months ago. I was told that if I disconnect the ECU's, I'll get the slowdown light but it shouldn't effect the performance of the car. The SD light will come on of course, but a quick removal of the bulb will take care of that. Correct?

 

lol ...... yes removing the bulb is one way to 'take care of that' ... ...... the temps should be between 180-200°F after full warm up ..... but since you just changed the thermostat you 'should' be ok. But I have actually seen some thermostats, be out of spec right out of the box.
Can you give any scenarios of when the slow down light comes on?

 

The SD light first came on when I started the car in the garage the day after a lengthy road trip (170 miles), but it went out right away. Early evening drive of about 30 miles with no issues. On the return trip however, the light came on and the motor was affected immediately after starting home. I pulled over and shut down the engine. Upon restart, it ran well for a few minutes and then I hit the freeway. 5-8 shut down shortly thereafter, but then came back after I slowed down and took an off ramp. Back on the freeway with no issues, but then came back on and off all the way home. So it seems that the problem doesn't stem from a coolant temperature issue as it occurs before warm up. Sorry for the lengthy description, but I need all the guidance I can get. Thanks for the help.

Henry

 

Henry,

My car is a 98 so I'm not sure if we have the same parts....

I've had the SD a couple of times early this summer in a week or so period. I bought a new TCU with green potting (that's a way to tell if yours are original, the originals are black potted).

I've never installed it since the issue went away. I'm suspicious that I got it wet??? Anyway, apparently these go bad and it may be the case if you get the SD when the car is cold...

 

Check the connections Henry, take apart clean reinstall
Also check the the probe wire possibly frayed or pinched grounding out

 

my 2.7 & straight pipes -
ECU's would come on & off almost randomly.
Decided to untie the diverter valve and the ECU lights went away.
SlowDown only until I replaced the failing sensor.
hasn't been on since.

 

Where do you guys plug in the temp sensors if you have a straight pipe system? Does it just hang out in the air?

 

I think some guys have bungs on the straight pipes so the sensors are still in line

 

I have hollow OEM cats cans on my 2.7. No SD light.

 

Thanks guys. I'll check the connections and clean them out as a first course of action.

 

OK, I cleaned the ECU-Thermocoupler connection and re-installed it. Got another SD light, so I took out said combination and the dash bulb. All is now well. I realize that it's not the most responsible fix, but I plan on it merely being temporary until I can buy a new ECU (mine has the green potting by the way).

A (kinda) funny aside. While working on the ECU I placed my socket set on top of the air box and eventually knocked it over while moving the air breather tube out of the way. I managed to recover nearly all of the sockets, but four of them eluded my flashlight and extendable magnet. On my test drive, it was raining sockets down the highway. Glad no one was following me. Actually tried to find them, but no luck.

Bottom line is that the car runs great right now, so thanks again to all of you for the responses and insight.

Henry

 

If you have a hand held digital pyro-meter, check the temps of the exhaust manifolds at each collector. On unshielded manifolds, they should be around 400°F to 500°F and ideally not more than 50°F apart from each other. If either side is above 500°F there may be misfires and/or a rich condition.

If you have stock manifold shields, the numbers above would differ slightly. I have not measured what stock shielded manifolds would read under ideal conditions.

 

I have ceramic coated Fabspeed headers with non-coated straight pipes.

 

Ok, ceramic coated should read slightly lower than uncoated, but I believe will still be within the temp range I noted above. The reason I am asking for a pyrometer temp measurement, is because we are trying to verify if it is a temp sensor (vescovini/SDL) issue or an 'actual' over-heating cat/exhaust problem.

I should clarify, the pyrometer temp readings should be taken 'just after' the collector and just forward of the axle (where the manifold reduces down to one tube, on each side). This can be done during idle, right after full warm up or right after a normal drive. Take several readings and average them for each side. Note: Don't let your car sit at idle too long.

Do you have a CEL? If you do, post the codes.

 

No CEL's. I'll see if I can borrow a temp reader from someone and check it out. One reason that I think that it is a bad ECU is that my left turn signal started blinking really fast when I got the SD light. Perhaps indicating an electrical issue? Turn signal back to normal once the ECU was disconnected. Thanks Bruce.

 

That blinking issue I have not heard of .... maybe a bad ground? .......... yes, exhaust temps using a hand held pyrometer, should give additional data on this 'potential' problem ......