I have a 91 Lumi with the 3.1. The ride only has 51,000
on it as I don't drive ti very much at all. Late Mother's
ride. Anyway I needed to get a part for my truck.
I took the Lumi. In the past it developed a miss at
idle but seemed to go away at higher RPMs. Also at
idle it surged. I replaced the plugs and wires, an
O/C and checked the vacuum lines due to being up
for smog. I haven't been able to get rid of the surging
or missing.

I took the ride out to get the part for my truck,
and when I tried to pass a truck on the freeway,
it reved up and started to move out, then it was
just like someone turned off the key. It started
bucking and shutting off. I was able to nurse it
almost home while it was missing badly and shutting
off . Then it just stopped. I tried to get it lite
off, but to no avail. It will crank and turn over,
but not run. I'm thinking either fuel or ign.

The pump is orig, the filter was replaced last yr. Is there
a part either in the ign or the fuel system that is prone
to failure more so than others ? I'm going to run a test
lead fused, from the pump diag terminal to the battery
to see if it will energize and see what pressure is. I'm
thinking pressure has to be around 60 or so for this
engine..I don't know.

Does the ign control module where the coils sit fail
often ? I'm new to the 3.1 SFI, but have worked
on my 4.3 a lot so I have a little bit on an idea where
to start, but am open big time to replies from you folks
who have run into a troublesome 3.1 before..

Any help or advise is most appreciated.

Thanks, n2gc.

First thing to do here is test the fuel pressure, 37 psi, but do it when the problem occurs, start there and post back results.

Well I got it running. Changed out the fuel filter
and it lit off. Problem is when it warms up it starts
to miss and tries to shut off, but catches itself and
keeps running, then finally after a few minutes it
quit and now won't lite off. Fuel pressure at crank
is 42 to 45 and holds pressure at 44/45. I feel it's
in the module where the coil packs sit on. I believe
it's heat sinking after it warms up from the exhaust
manifold and shorts out. GM could of found a better
place to mount that assembly rather than almost
right on top on the front bank manifold.

So it's either that or a issue once it goes into closed
loop. I wiggled wires here and there, save for the
wiring going into the ign module. I suppose after
it cools down I'll try that, but it's electrical I'm
fairly certain. Time will tell, but I'm getting this
thing running, one way or another..

After getting prices from 125.00 to 305.00 for the
ICM, I finally found a new Delco OEM for 52.00
shipped. Going to install it and see if it helps the
ride run. Does any kind of heat sink dope go on
the module before the coils do ? I know on my
truck I use Arctic 5 chip to heat sink dope from
my PC for the ign module to dist base and it's
worked great for protection. I don't want to
fry this new module because I didn't put protection
between it and the coils.

By the way, does the fuel tank have to be dropped
to get to the pump, or did the General have enough
sense to factory punch a hole in the body to access
it from the top ?

Yes between the icm and the mounting plate, tank must come out for fuel pump.

Thanks for the heads up on the heat sink info..
tank must come out for fuel pump.
Rats.

I haven't got to it yet, but looking around I came upon
this. Looks like inj's fixed this guys ride.
http://60degreev6.com/forum/showthread.php?t=34118

Then I went over to Lindertech and did some looking
and came upon this.Check out the first statement
regarding 2.8 3.1 engines 90/93..Wonderful.
So if this ICM doesn't solve it, I may send in
the inj's and have tested. If bad, in go Bosch
DRI's.
http://www.lindertech.com/pattern_failures.htm

Been a while since I've posted on this deal. Tried the ICM today and it didn't
fire. I have 45 PSI coming out of the pump at the fuel rail. I have a test plug
I use to check spark. Used it and saw to spark firing. Tried it after a while and
got one spark out of the test plug and the ride tried to lite off, but then the
spark didn't show again and of course it just turns over. I did coat the
module with heat sink dope like I use on my 4.3.

I'm wondering if the "new" [ebay] module I bought is defective ? I also
wonder if I should just go with a new one as well as replace the coils ?
They are OEM from 91. I've checked the fuses, relays and gas is flowing.
Are these rides infamous for the ECM's to fail ? I hate to throw money
at this thing.

I wonder if a faulty oil pressure switch would kill the spark. I know it
will with the pump if it doesn't see spec'ed oil pressure. This is getting
a lil frustrating. Can someone point to where the ECM is ? I think I'll
pull it down and check the plugs for crap buildup. Wish I had a PROM
to go into it besides the one that's in there now.

By the way, I checked out the ECM and Ign fuses
over on the right side and the relay and 20 amp fuse on the left side.
All appeared to look good. I did note that there are fusible links down
yonder trailing towards the back of the engine. I wonder if one of those
gave up the ship. Seems strange I got spark for a second then no spark
before or since.

Thanks for any input, tips, advise or leads.
bg

update
I went out with my scan tool, not the best, but it gives data streams, and
while cranking I was seeing a IPW of 25.9. Does that sound right ? It seems
like it's excessive. Could it be going into clear flood mode shutting down
the ign ? I can hear the pump and pressure is still around 45. It's getting
fuel, and almost lit off, but spark stops. Oh how I wish this were my old
4.3 TBI. I'd be done with it by now.

Any good input regarding IPW and clear flood parameters is most welcomed.

Thanks

Did you see cranking rpms on the scanner, If so I would suspect the ign module here. On a cold start ther ipw is very high, also clear flood will only happen foot to the floor during cranking. Yes ecms were troublesome for sure, try tapping the case with a screw driver handle see what happens.

OK first off this is a '91 so it should be a 3.1 with MPFI but not SFI like the '93-up 3100.


Been a while since I've posted on this deal. Tried the ICM today and it didn't
fire. I have 45 PSI coming out of the pump at the fuel rail. I have a test plug
I use to check spark. Used it and saw to spark firing. Tried it after a while and
got one spark out of the test plug and the ride tried to lite off, but then the
spark didn't show again and of course it just turns over. I did coat the
module with heat sink dope like I use on my 4.3.

Fuel pressure's fine. So you have no spark at multiple plugs?


I'm wondering if the "new" [ebay] module I bought is defective ? I also
wonder if I should just go with a new one as well as replace the coils ?
They are OEM from 91. I've checked the fuses, relays and gas is flowing.
Are these rides infamous for the ECM's to fail ? I hate to throw money
at this thing.


You should test them first before replacing them. The ignition module can be tested at an auto parts store. The coils can be tested with a voltmeter.


I wonder if a faulty oil pressure switch would kill the spark. I know it
will with the pump if it doesn't see spec'ed oil pressure. This is getting
a lil frustrating. Can someone point to where the ECM is ? I think I'll
pull it down and check the plugs for crap buildup. Wish I had a PROM
to go into it besides the one that's in there now.


No the oil presure switch will not kill the ignition, just the fuel pump. The ECM location varies but I think on these car line it's under the hood on the passenger side inside the fender. but don't worry about the ECM or prom for now.


By the way, I checked out the ECM and Ign fuses
over on the right side and the relay and 20 amp fuse on the left side.
All appeared to look good. I did note that there are fusible links down
yonder trailing towards the back of the engine. I wonder if one of those
gave up the ship. Seems strange I got spark for a second then no spark
before or since.

Thanks for any input, tips, advise or leads.
bg


update
I went out with my scan tool, not the best, but it gives data streams, and
while cranking I was seeing a IPW of 25.9. Does that sound right ? It seems
like it's excessive. Could it be going into clear flood mode shutting down
the ign ? I can hear the pump and pressure is still around 45. It's getting
fuel, and almost lit off, but spark stops. Oh how I wish this were my old
4.3 TBI. I'd be done with it by now.

Any good input regarding IPW and clear flood parameters is most welcomed.

Thanks

IPW you mean injector pulse width, right? Whether 25.9 is high depends on if that's milli-seconds scale or not. I think normally it would be at 1-4 ms at idle but on cold start it might go that high. Clear flood mode would give near 0 IPW and about the only thing that would make it go in clear flood is if the ECM think the throttle is floored-this would show as high TPS voltage like over 3 volts. What having an IPW also tells you though is your crank sensor is probably working and your ICM is getting power. As a second check, can your scanner display RPM during cranking? Check for spark at plugs 2 and 4 or 4 and 6, diconnect one at a time and test. Provided you're getting a steady reference for RPM, no spark from both coils would indicate a bad ICM. Maybe take it to an auto parts store to have it checked.

Thanks for the advice and tips. I'll try the 2/4 test plug combo. I really only
tested num 1 to see if it would spark. It did once and that was it. I saw crank
rpm from the scanner via the crank sensor. It was showing 179 to 198.
I'll have to data stream it again while cranking to see if in fact I'm getting
any rpm signal. I'm going to undo the ground, pull the ECM out [I'll ground
myself] and undo the various connectors. It might just be something there.

The ICM was "new" [An eBay deal..] and looked good, but who knows. I'll
look up the tests for the coils. Yes I was referring to injector pulse width.

We'll see how it goes. Right you are about it being MPFI. Why I thought
it was SFI is confusing. I've read up a bit on the Gen II's and III's and now
see it did go in later. What I find odd is that it has a MAF and a MAP on this
ride. I suppose the MAP was used for a backup to the EST for timing advance ?

Thanks again
Bg

Thanks for the advice and tips. I'll try the 2/4 test plug combo. I really only
tested num 1 to see if it would spark. It did once and that was it.

The number 1,3,5 plug wires are on the firewall side, so th 2,4,6 is n the radiator side. And 2 and 4 are on different coils so the idea is they are easier to get to and you'll be checking for spark at two coils.



I saw crank
rpm from the scanner via the crank sensor. It was showing 179 to 198.
I'll have to data stream it again while cranking to see if in fact I'm getting
any rpm signal. I'm going to undo the ground, pull the ECM out [I'll ground
myself] and undo the various connectors. It might just be something there.



If your scanner was getting an rpm signal then you are getting the data stream. Power is going through the module to the crank sensor. If you're not getting spark on 2 wires from 2 coils then it's all pointing to a bad ICM. There's no need to fiddle with the ECM or the grounds till you get the ICM problem sorted.


The ICM was "new" [An eBay deal..] and looked good, but who knows. I'll
look up the tests for the coils. Yes I was referring to injector pulse width.


Well there are some shady sellers on Ebay, and sometimes a new part can be defective. You are entitled to a refund plus there's the feedback option.The diagnostics is indicating a bad module so far.Take the module off and have it tested at an auto parts store.


We'll see how it goes. Right you are about it being MPFI. Why I thought
it was SFI is confusing. I've read up a bit on the Gen II's and III's and now
see it did go in later. What I find odd is that it has a MAF and a MAP on this
ride. I suppose the MAP was used for a backup to the EST for timing advance ?

Thanks again
Bg

all GM FI have at least a MAP, even some of the old carbureted applications had MAP if they had electronic spark control (although those might have been built into the ESC module). The MAP does take the place of a vacuum advance canister, but it's also a main sensor to calculate air flow and can take the place of a MAF. Later-models like the 3100 have both a MAF and MAP. Are you sure your '91 has a MAF? I would think only the '93-up have a MAF. As far as I know, prior to that only the TPI V8's had MAF.

Thanks for your input. I will have to look again, but now that I think about it,
I don't believe it does have a MAF. I believe it's just a throttle body for o2
with an IAT and perhaps the MAP is doing it's thing like a speed density
system. I'm going to work on it this weekend again. I'll have to call around
and see if Autozone or Kragens tests ICM's. The spark test off of 2/4 should
help get closer to finding the probs.

At least I'm learning and it hasn't cost too much yet.

Thanks, again.
bg

The changover to the gen. II 3.1 was made during mid production run for the '93 model year. You have been talking like it was all '93 models.
If pulling ECM, only pull the fuse in the glove box panel, as pulling the grnd. will cause need to reprogram some of the sensors, especially IAC.

The changover to the gen. II 3.1 was made during mid production run for the '93 model year. You have been talking like it was all '93 models.

Who's been talking like all '93 models were changed over to 3100? What I said was that the 3100 didn't come out till the '93 model year. It's generally understood that a change over happens through out the model year or longer.

If pulling ECM, only pull the fuse in the glove box panel, as pulling the grnd. will cause need to reprogram some of the sensors, especially IAC.

That's true if you disconnect power to the ECM the IAC and the fuel block learn values will have to be relearned, but pulling the ECM fuse will disconnect power to the ECM too. The IAC will probably relearn its self as wil the block learn. Anyway, I advised that the ECM didn't need to be fiddle with right now to begin with.

Thanks, guys. Yea I'm going to concentrate on the 2/4 test fire and the ICM.
Haven't found a place that tests the ICM but continue to search. I've pulled
the ground a number of times when changing out elec items. An IAC relearn
and whatever else it req's will get done once I get it to lite of. Any chance the
crankshaft sensor is causing this ? I'll try and get a screen shot of my old
scan tool when cranking the engine and post it up.

Thanks again.

Thanks, guys. Yea I'm going to concentrate on the 2/4 test fire and the ICM.
Haven't found a place that tests the ICM but continue to search. I've pulled
the ground a number of times when changing out elec items. An IAC relearn
and whatever else it req's will get done once I get it to lite of. Any chance the
crankshaft sensor is causing this ? I'll try and get a screen shot of my old
scan tool when cranking the engine and post it up.

Thanks again.

As I explained earlier if you are getting a cranking RPM reading from the scanner then your crank sensor is working and being powered through the ICM, and so your ICM is getting power also. This is why I said if you don't have spark on two or more coils then the ICM is indicating bad regardless.

Have you checked for spark on 2 and 4 or 4 and 6 yet? Most of the auto parts stores around me test ICMs, you probably have different stores where you are. The ICM doesn't even need to be tested off the car really. If you have crank signal which you're saying you have and if you don't have spark form any coils, then the ICM has tested bad by the process of elimination.

Thank you for your definition of two or more. I haven't had an
opportunity to test the coils. I plan to this weekend. I'm in hopes
of getting this thing going as I have Ca Smog coming up sooner
than later.

Thanks again,
bg

I took the orig ICM up to have tested. Found a place that does it and
it showed good. CRAP. So now I'll test the coils with them hooked onto
the ICM that's on there now. But so far it has not panned out to be an
ICM. [It was doing the same thing with the orig ICM. That's why after
reading a few things, I picked up another. Doesn't make much sense,
but I do dumb stuff like that]

I still think I should look at the plugs and pins of the ECM. I washed the
engine a few times a year ago, and maybe that's what is causing the
probs.

Well did you ever test for spark at 2 or more coils? If you were getting no spark but were getting a crank signal, it has to be the ICM. Something is not adding up.

No I haven't had a chance to test the coils as suggested. I had the old
ICM with me during a work run and managed to find a place that
tested it. It showed green. One thing I was amazed at was how fast
it warmed up. It didn't take but a couple of minutes for the test and
the back was quite warm. Did GM ever put any kind of dielectric
grease or some kind of insulation between that back section of the ICM
to the alum mount ? Didn't seem like it. No wonder those things don't
last.

No I haven't had a chance to test the coils as suggested. I had the old
ICM with me during a work run and managcheck to find a place that
tested it. It showed green. One thing I was amazed at was how fast
it warmed up. It didn't take but a couple of minutes for the test and
the back was quite warm. Did GM ever put any kind of dielectric
grease or some kind of insulation between that back section of the ICM
to the alum mount ? Didn't seem like it. No wonder those things don't
last.

Well it seems like you originally had one problem then when you changed the ICM you got a no start, right? Your original ICM might not have been bad (depending on how reliable the autoparts store test was), but the replacement one could be. If you have a no start problem, you need to check for spark. It's simple to do. All of the 3 front plugs are pretty easy access and each runs to a different coil.

I agree and am going to do the testing this sat morn. I need to get to the
bottom of this if for no other reason than it's very irritating to have a 1991
car with only 50,000 miles on it just rotting away.