Car seems to be stuck in limp mode...

[1mz]

Hey guys, long story short I have someone else working on my car at the moment to finish up my swap and he is having the following problem:

Car:
1991 318i
1992 NV M50 - green label '173' ecu (I'm pretty sure, I have to talk to him to check)

Problem:
It seems to 'redline' around 3000 RPM's, and won't go over 20 mph

I am putting together a list of things to check tomorrow and I have considered already:
- is there a problem with the ecu?
- did a crank or cam sensor go bad?


I am calling on the knowledge of the internet - what else could be causing this issue?

[Sagaris]

Low fuel pressure
Clogged cat

[1mz]

Low fuel pressure
Clogged cat

no exhaust on yet, just headers, and I'll be sure to check the fuel pressure/pump tomorrow

[MR 325]

Definitely can't be a 173. Did you hook a scanner to it?

[7pilot]

Road speed data unavailable to DME?

m

[Lof8]

Road speed data unavailable to DME?

m

I had to wire in a separate vehicle/road speed signal to my dme by taking a signal from the back of the speedometer.

Any easy way to check if this is your problem:
disconnect the battery for a couple minutes to allow the dme to reset.
Hook the battery up and go for a spin. If the car runs fine for 5 minutes and then hits the 3k rpm limiter again, it is going into a limp mode due to no VSS.

I was under the impression this issue was only in the older cars, though, so this may not help you.

[1mz]

Haven't checked codes yet, thats happening sometime this week - I'll be sure to post whatever comes up. I'll have him check the speed signal as well, thanks for the help guys, hopefully it'll get sorted out soon.

[SamE30e]

On non vanos late model swaps, you shouldn't have to run that wire.

[herlsy]

Did you switch your coding plug?

[Adrian_Visser]

Another way to check if the DME is getting a vehicle speed signal is to put the car in neutral and watch the idle when you are moving, the idle should stay up at about 1000rpms when moving and then drop down to 750rpms a second or two after you come to a complete stop. You should also get a CEL. Who made your wiring adapter?

I wouldn't expect the car to run very well with no exhaust though my s52 had no balls open header with no O2 hooked up and it idled like it had a huge vacuum leak.

Bottom line: Get the exhaust sorted before you worry about the fine details of it running properly.

[flyboyx]

I had to wire in a separate vehicle/road speed signal to my dme by taking a signal from the back of the speedometer.

Any easy way to check if this is your problem:
disconnect the battery for a couple minutes to allow the dme to reset.
Hook the battery up and go for a spin. If the car runs fine for 5 minutes and then hits the 3k rpm limiter again, it is going into a limp mode due to no VSS.

I was under the impression this issue was only in the older cars, though, so this may not help you.

disconnecting the battery likely will not reset your dme. you need a reset tool for that. i am guessing you do not have your check engine light hooked up? you really should get your hands on a peake scan/reset tool or equivalent. since you haven't mentioned any fault codes, i would have a tendency to assume you do not know what they are? having this info would be critically important at this juncture in your swap. without it, you are pretty much just taking a shot in the dark. also, there is a pretty good possibility that if you reset your codes, the engine may run fine.

[Adrian_Visser]

On non vanos late model swaps, you shouldn't have to run that wire.

Do you mean that NV DME's don't use the vehicle speed signal or that you don't have to run a wire from the tach/ c104 connector on late model cars?

disconnecting the battery likely will not reset your dme. you need a reset tool for that. i am guessing you do not have your check engine light hooked up? you really should get your hands on a peake scan/reset tool or equivalent. since you haven't mentioned any fault codes, i would have a tendency to assume you do not know what they are? having this info would be critically important at this juncture in your swap. without it, you are pretty much just taking a shot in the dark. also, there is a pretty good possibility that if you reset your codes, the engine may run fine.

OBDI DME's will reset themselves if you disconnect power for ~15min. OBDII DME's will not and need the codes to be cleared with a scanner.

[SamE30e]

Do you mean that NV DME's don't use the vehicle speed signal or that you don't have to run a wire from the tach/ c104 connector on late model cars?



OBDI DME's will reset themselves if you disconnect power for ~15min. OBDII DME's will not and need the codes to be cleared with a scanner.

I'm pretty sure NV's don't use vehicle speed sensor. I think it's only used in vanos engine so vanos doesn't activate when the car isn't moving i.e revving the engine while stopped. I know I never ran a wire and my car moves just fine, isn't in any limp mode, no check engine light.

[Adrian_Visser]

I'm pretty sure NV's don't use vehicle speed sensor. I think it's only used in vanos engine so vanos doesn't activate when the car isn't moving i.e revving the engine while stopped. I know I never ran a wire and my car moves just fine, isn't in any limp mode, no check engine light.

Good to know. I wasn't too sure.

[1mz]

Guy is dragging ass... *grumble* BUT I was layin in bed falling asleep the other night and had a "slap-in-the-face" revelation. I completely forgot that earlier this year, the very FIRST time I went to try and start the car, there was a ground issue that burned out one of the wires going to the MAF - I replaced the wire, but completely forgot about checking the MAF....

My aunt has a NV e36, I'm borrowing her MAF this weekend and I'm gonna give that a try