3400 Fiero Swap Starts ... sometimes

[neophile_17]

Hello,

I'm almost there with a 3400 in my 85 Fiero. I got the engine to start for the first time yesterday. However I shut it off to top off the coolant and it didn't want to start again. After messing with it a little, I pulled a plug to check for spark. It started again with a plug out. Put it back in and it won't start. Should I be getting an RPM in TunerPro while cranking? I do not. When it was running I got correct RPM readings. Thank you for any guidance you can provide.

~sam

[neophile_17]

Well unless someone out there has any insight I'm going to go about things like this. Remove ICM to have it tested, and buy a crank sensor while there. Go to the JY and get another 7730, crank sensor wire and ICM if it tests bad. Pray.

~sam

[SappySE107]

Yeah that doesn't really make any sense to run once, then not run unless 1 spark plug is pulled. Are you sure its getting enough fuel?

[phonedawgz]

A quick indication of if the ECM is getting ignition pulses is to bump the starter and see if the fuel pump relay gets activated. It should with every bump of the starter. The fuel pump should run for two seconds after the last ignition pulse that the ECM gets.

[neophile_17]

Well I went to grab the ignition module last night and figured I'd try it once. It started right up. So I let it run a couple minutes and shut it down. Finished adding coolant and it started up again. Figured maybe it was heat sensitive so I let it heat up and it still started without issue. At this point I'm somewhat at a loss. I have a couple tenative theories as to what was preventing it from starting.

Battery voltage was low causing something to flake out.
Rings needed to be re-seated.
Bad parameters from running on 5 cylinders didn't clear after 30 seconds of no power.
Having my battery charger charging freaks out some piece of electronics.

None of these theories seem particularly satisfying but I'm hoping to test drive it tomorrow. Really wish I had an answer with some confidence behind it.

Thanks for the tip about the fuel pump. That's exactly the type of test I was hoping for.

At least some fuel pressure was in the system but I ordered a fuel pressure guage and it should be here next week.

~sam

[pocket-rocket]

To answer the question on TP reading RPM while cranking, I'm not 100%, but I'm fairly certain it should since the ECM should be seeing rotation to know to fire injectors and plug. I don't believe the low RPM engine starting process is hardwired into the ECM.

The fuel pressure gauge, is that an installed type to install on the car, or the test type that you can hook to multiple cars for troubleshooting? They can be an invaluable piece of troubleshooting hardware

[neophile_17]

The pressure guage is the troubleshhoting variety not a permanent type, I'm excited.

So I buttoned everything up for a test drive and guess what, no start. I guess this is what I wanted...

Using phonedawgz test method I confirmed that the ECM isn't getting a signal from the ICM. I pulled the module like I should have before and will have it tested. Thanks.

~sam

[neophile_17]

So I took my ICM to 2 parts stores to have it checked and both looked at me like I was crazy. I did order a crank sensor.

I ohmed out my coils and got 5650-5800 ohms for each secondary winding and .2 ohms for each primary. Haven't been able to locate the spec but they're so similar I imagine that's good.

I happened to pick up somewhere that the timing programmed into the ICM advanced slightly around 97-98. When I go to the JY for a spare should I pick up an earlier ICM?

Thanks.

~sam

Oh, got my fuel pressure tester.

[phonedawgz]

http://www.wellsve.com/video_gmcylmisfire.html

They get into 'no fire' towards the end.

[neophile_17]

Good Info.

They recommend .5V from the CKP sensor and I only get .3V which another source indicated was just in spec. I'm also going back to the battery since the CKP sensor increases in strength with RPM. I'll have to get it checked out. Thanks.

~sam

[hookdonspeed]

i think i have an extra icm laying around, ill have to look for it, if u wana barrow it for testing.... btw. i work at a parts store but we dont do any testing...

[neophile_17]

Thanks for the offer. I think I'm just going to pick up some spares at the yard though. This won't be my last swap and the car is so far from a parts store it's worth it. I'm also thinking my starter needs to be shimmed out a little. Maybe that's contributing to a slow cranking and no signal. Hopefully I'll find out Saturday. Yeah, in all the other threads about the ICM problems everyone says to take it to the parts store and they'll check it. None around here seem to...

~sam

[Z3500]

I would bet its a loose wire or bad connection somewhere.

Double check your grounds.

[neophile_17]

So I shimmed out the starter a little and that increased my cranking RPM but no start persisted. I replaced the crank sensor and I haven't had an issue since. I'm going to need a little help with some fine tuning. Datalog to come.

~sam

[neophile_17]

Hello,

First of all I'd like to thank Ben profusely for offering his tune for sale. The car runs almost flawlessly. I ran into a couple of small issues that I'm sure will turn out to be my fault as they have so far. When I wired everything up I wired the VSS directly to the ECM as Sinister Performance does. As a result I hit the MPH barrier at 75 instead of 150. Easy enough, just switch the from 2000 PPM to 4000. The other issue I have is that when coming to a stop I often get a stall condition. This may be a result of the mph error but I'll post my datalog in case anyone sees something weird.

http://www.rustytearracing.com/3400_stuff/Tune/rain.csv

The stall occurs between record 4000 and 4050. Any advice is appreciated.

~sam