[mikemo]

Hello all. New guy here trying to help a friend fix her 2001 Sentra (1.8 auto). She has owned the car for 3 years and it has just over 100k miles on it.

She was complaining about it stalling at lights and stop signs occasionally. She said that it got "worse" and would run poorly. I went to look at the car and confirmed what she saw. It ran fine when cold, but after warming up it would sometimes stall when stopped, but the major problem was that after it was hot the engine lost most of its power. The engine would surge and chug, but never rev over 1500rpm or so. It never completely died, but it was hard to go 20mph.

The check engine light was on so I took it to an auto parts place to read the codes. They were unable to read them. Then I used a small cheap code reader and had the same problem. It could not connect to the ECU.

I followed the troubleshooting instructions for the obdII port and measured the proper power and ground, and the data line was at 7.5 volts which is close to what the book said (book says around 8 volts). We reseated the connector on the ECU but it didn't help.

I don't have a spare ECU to swap in, and there were none at the local junkyard, so we gave up on getting the code reader to work. I took a guess that one of the coils was failing. We bought one new coil and swapped it in to each spot, but the problem persisted. $80 down the drain.

I don't want to just throw more money at this, but without being able to read the codes I have no idea what the computer is not happy with. So, two questions:

1) any ideas about not being able to read the codes?
2) Any hints on what could cause the bad hot-running condition?

Sorry this is so long, but I wanted to include the info I know.
Thanks in advance for any help
Mike M.

 

[JudoJohn]

it's hard to guess w/o codes. but i would check ALL the grounds in the engine compartment. look closely at the wiring. sounds like thre might be a broken wire- perhaps to the ECU.

another thing to consider is the Crank pos. sensor and cam sensor. they acan cause a lota havoc and are eawsy to replace.

 

[i68k]

yea, its hard to tell without any codes. could be anything from bad cps, to a bad ecu. i would start and make sure the battery terminals are super tight, and has good ground contact. check the voltage with motor on & off as well. dont forget headgasket failure is also a problem, except it usually runs like crap until it warms up.

 

[rogergm62]

check all the wires form the ecu to the connector... or do a re-wiring..... if this does not work... try to find another ecu on ebay....

 

[i68k]

if you cant read the codes thru the obd2 port, its usually either connection, fuse, or ecu, or a bad/cheap code reader. hopefully youve tried multiple code readers.

 

[mikemo]

Thanks for the advice guys.

We tried my code reader (cheap) and Autozone. Both would not read codes.

The fuse is good as I have power on the ODBII connector.

The problem only happens when hot. Still think it could be grounds? I'll clean them all up anyway just to make sure.

We replaced both the crank and cam position sensors. $50 for both and easy to swap, but it didn't fix it.

I tested the TPS and it appears to be fine.

Perhaps the MAF? What kind of symptoms could I expect if it was bad.

Anyone in the Tampa area want to let us swap our ECU into their car and see if it works?

Thanks again
Mike M.

 

[i68k]

normally with a bad maf, it usually loses idle, or youll get an idle bounce. but seeing this is automatic, its hard to tell. what does it idle to in neutral when the car is warm? does it idle correctly? you should pull the ecu out, and examine the box, the early 1.8s are known for rusting up the ecu, and seeing you have power and good fuse for the obd2, the ecu may be the problem. however, it is not a cheap part, make sure you match the code on the ecu, something like k2, 5p, etc. for the ecu, youll need to know if its cali or fed emission, and whether or not you have nats. i believe the production date is a good thing to know as well.

 

[mikemo]

The ECU is very clean. No rust at all.
The ECU is stamped with "N3" on the top. It is also written with marker on the ECU bracket. Not sure if that was done during production or if someone had been in there already.

Once hot, it seems to idle fine in park or neutral. Put it in gear and it may stall. If you just touch the gas it will put-put along, but if you press on the gas the motor falls on its face, surging between 1000 and 1500 rpm. It can barely do 10mph. When cold, it runs normally.

Are the cheap MAF sensors on Ebay worth a shot? Looks like I can get one for around $30 instead of $250 from autozone.

Thanks!
Mike M.

 

[JudoJohn]

My advice: don't buy auto parts from ebay! it may be cheap, but if it is the wrong part, can you get your money back? GO to Rockauto.com and see what they have.