Author Topic: Runs but wont start if stopped [NOT evil cat. plug] (Read 8402 times)

KidneyBoy · « **on:** January 10, 2010, 11:13:54 AM »

Im working on a car i sold to a friend about a year ago. I rebuilt the head and gave him the car in good working order.

Since then, it has had an issue where it will not start after running a short distance. I had thought it was a charge/draw issue and worked to solve this. It now holds a charge [which it did not before] but if the car is started and ran around the block [1-2min of run time] then stopped it will not start.

Cranks and tries to fire. Sputters while cranking, once cranking is stopped it continues to chug for a second or two then dies. Has fuel, has spark.

DesktopDave · « **Reply #1 on:** January 10, 2010, 12:29:01 PM »

I know it gets fuel, but double-check to see if the fuel pressure is good.

I've heard of a BMW fix that puts a valve in the output line off the tank pump. Here's a write-up. The pump bleeds off pressure after a warm start & the car takes forever to start.

KidneyBoy · « **Reply #2 on:** January 10, 2010, 01:59:19 PM »

Well, the fuel pressure should not cause it to act that way [going to check pressure anyway]

It literally will run like a champ [perfect idle, good power, smooth, quiet, etc.] but if you turn it off then immediately try to start it again it will not start. it cranks and cranks, tries to fire and sputters out.

Wait an hour or so and starts on the first try and runs great.

DesktopDave · « **Reply #3 on:** January 10, 2010, 02:33:13 PM »

Well, let me know what you find. Post stomp test results too...could be a flaky coolant temp sensor, FPR or leaky injectors too.

I suspect that the pump is a little slow to pressurize the system on warm starts but it's just a hunch.

KidneyBoy · « **Reply #4 on:** January 10, 2010, 03:12:23 PM »

the PO removed the wiring for the check engine, i cannot find it anywhere behind the cluster. i was thinking the temp sensor or coils.

KidneyBoy · « **Reply #5 on:** January 10, 2010, 05:09:40 PM »

Fuel pressure figures...

50lbs when cranking
40lbs @ idle
35-45lbs while running
36lbs when turned off

Then when it wont start
50lbs cranking
46lbs after cranking

DesktopDave · « **Reply #6 on:** January 10, 2010, 05:30:48 PM »

Those pressures sound great. FPR & fuel system check out.

Temp sensor on head or O2? Maybe the temp sensor is reading too warm (or O2 too low) & the DME isn't injecting enough fuel? Odd that the pressure remains high on the warm start.

Maybe the O2 heater or relay is dead & not warming up fast enough? If the car is hot the O2 will be in normal closed-loop mode. If it's warm the reading might be off, leaning out the mixture & keeping the car from starting? Just a guess...

KidneyBoy · « **Reply #7 on:** January 10, 2010, 05:49:18 PM »

can you give me some figures to check?

crank/cam sensor ~600ohm
afm 4k-8k between pins 1 & 2
TPS 1.9-5v

Whats the range for the temp sensor?
02?

Ive got a spare ECU/DME that my friend is going to let me try.

Some more info.... I can start the car, let it run for 30 seconds then restart it all day long. It has to run for about 2 minutes before it wont start. After about 20-30 minutes it will start fine.

KidneyBoy · « **Reply #8 on:** January 10, 2010, 05:56:41 PM »

where are the ground for the engine harness?

i know of the one near the pass tower [where the battery used to go] and another off the pass motor mount. are there any others?

KidneyBoy · « **Reply #9 on:** January 10, 2010, 07:04:44 PM »

I may have the crank and cam backward

Crank Sensor - 1257 ohm
Cam Sensor - 508 ohm

AFM checks out, in range from 4k to 8k then back down to 4k

TPS 4.72v to 1.17v

ECU temp sensor - 620 ohm cold

How do i check the coil packs?

DesktopDave · « **Reply #10 on:** January 10, 2010, 07:29:43 PM »

I've never tested the packs. I'd pull the plugs out, reconnect them & ground them to the engine to see if they spark. I'm sure there's a better test, but I haven't ever done it any differently.

The sensors you tested seem OK, readings all are pretty normal. Crank & Cam values are reversed. Did you test the O2 heater relay?

KidneyBoy · « **Reply #11 on:** January 10, 2010, 08:57:11 PM »

How is the o2 heater relay checked?

sorry for coming off as 'needy' but im quite tired of this car

KidneyBoy · « **Reply #12 on:** January 12, 2010, 04:08:49 PM »

Okay, I've done a bit of work on the car since the last post.

Heres what I've found...

Car runs fine after sitting for a while but will NOT restart after being turned off.

CPS, CMS, ECU temp switch, AFM are all in good working order.

What Ive found in playing around, is that the engine floods when turned off. I have swapped FPR's with no luck. The fuel pressure is good [40lbs] and will hold 40lbs after the car is shut off.

However, if you pull the fuel pump fuse [#11] and crank the car after it has been turned off, it will start and run until the injectors use the fuel in the rail.

So Ive concluded that the engine could be doing one of two things. It is either dumping fuel on start up, but only after it has been turned off within about 5 minutes. Or when the car is shutting down, i.e. ignition cut = no spark, the injectors are still firing.

This has me very confused... I'm sure someone out there in internets land has an answer.

DesktopDave · « **Reply #13 on:** January 12, 2010, 08:29:51 PM »

Wait, let's think this through. What should the system be doing on warm starts? Hopefully it's not doing the whole cold-start routine, choking the engine. That'd flood it and stop it from starting. The DME should interpret from the coolant & IAT sensors what to do, how far to richen up the mix. Coolant sensor checks out at all temps, right? I found these figures at bimmerforums, not sure if they're right:
-10 +- 1C.....7-11.6k
20 +- 1C.......2.1-2.9k
80 +- 1C.......0.27-.40k
They're for an e36, but it's likely the same sensor. I'm assuming ohms resistance.

Can you get a spare AFM?

Here's some info about the IAC sensor:
It is nothing more than a NTC thermistor, connected in series with a 1kohm resistor in the ECU...you can just use this one:
http://search.digikey.com/scripts/Dk...me=490-4665-ND
Isn't that from a member of this board? Stand up & be recognized if so...excellent bit of reverse engineering there!

The injectors should continue to fire even if the pump isn't on. They're fired from the DME & only pressurized by the pump. The FPR is mechanical, so the DME really has no idea about the precise fuel pressure/temperature or vacuum enrichment. Bosch & BMW do a lot of things like that...for instance the little MPG gauge is just a calculator figuring injector duty cycle against the speedo reading, corrected by the settings on the EEPROMs in the cluster & trip computer.

KidneyBoy · « **Reply #14 on:** January 13, 2010, 01:53:54 PM »

Well, it all seems to check out, do you know what pins i can back check on the AFM to make sure the internal temp is reading okay? Or even a reading, cause i can see the thermocoupler with the air box off.

I did fixed the wiring from the check engine light. The battery had been disconnected for some time and the car has only been started a handful of times since then.

Only code 1216 which is the TPS but could be the connector.

I may have to give the car back to my friend and have him drive it around occasionally doing a stomp test.