'88 GMS 1500 305/TBI help needed

The hell is a GMS? Need more coffee...

Ran fine all day yesterday, cranks but won't start this morning. Fuel pump and ignition module both replaced about two months ago by trusted shop, been running normally since. Nearly full tank of gas.

Suspecting a clogged fuel filter, I pulled the line to the TBI to check flow. The line flows strong for a second or two when the fuel pump primes in the ON position, but does not flow any gas when the engine is subsequently cranked. Is that normal?

The motor that runs when the ignition is turned either on off - it sounds like it's on the firewall on the passenger side, and it corresponds to the fuel pump priming - is that related to the fuel system? Cause it's been sounding like a wounded water buffalo lately.

Haven't checked for spark yet.

Happy birthday to me!

Well, Happy b-day....Someone pull a distributor wire as a birthday prank>

Welp, buttoned the fuel system back up, cranked it just for s&g's and it fired right up. I think I'll throw a fuel filter at it to make myself feel a little better.

Man, I hate when this stuff "fixes" itself without time for a proper diagnosis.

In reply to alex: That's better than when you can't fix it with time and proper diagnosis.

Chris

If it primes when you cycle the key, all the fuel system is fine. Since it does not run the pump when you crank it, you have lost the signal to the ecu telling it that it needs to start the fuel pump and cycle the injectors. Next time it quits, see if you have spark first. No spark equals no fuel, although it may have spark but no output signal to the ecu.

Was the new ignition module something other than an OE Delco unit? If so, take it out and beat it with a hammer till your arm hurts. The pain will remind you to not use cheap ignition parts.

Its to my understanding when it comes to non oe ignition parts, you're better off going to the pick and pull and getting a used one.

It's baaaack.

As I suspected, it didn't fix itself, but the problem is just intermittent enough to be a bitch to diagnose.

So, I threw a fuel filter at it last time it did this little routine, and it was running normally for over a week. Went out today: cranks, no start.

Since I'm fairly confident the fuel system is where it should be, I'm going to chase down Streetwiseguy's suggestion about spark/ECU signal. Any further thoughts on that topic will be most welcome.

We had this problem on our TBI'd lemons car. We put a fuel pressure guage on it. What was happening was the pump (brand new went through about 4 of them) was dying. It would supply pressure for a litle while (like 20 seconds or so) then teh pressure would bleed off.

Sometimes it wouldn't have enough pressure to start. Or it would start and die. it sucked.

Anyway, a pressure gauge would tell you if it was a fuel issue.

Rob R.

It's never started and died, and it's only died running once when the fuel pump went out, maybe 500 miles ago. I feel confident that the fuel system is sound, and the fact that it's priming properly but not flowing gas when cranked is a significant hint. But to what...?

Oil pressure switch (back of the intake by the firewall) can have some input on that. MAke sure there's a good connection (although I thought that was typically a no prime issue). Are you getting spark at the cylinders? The pickup coil could have taken a dump. If it was the ignition module, you'd have no fuel pressure as well.... but it could be a source.

Just found out I have no spark. Ignition module is 300 miles old (don't know yet if it's OEM), plugs and wires have less than a year/10k miles on them.

I'm thinking coil or pickup coil, but that's a blind guess. Tonight's reading material is the Chilton manual, and I'll do some more poking in the morning.

Its likely the module( which is probably Chinese), but check the coil resistance as well. Too low resistance= too much current.

I'm reading that a failing coil will cook an ignition module in no time. Sounds like a good place to start.

Okay, check my work.

The coil fails all three test for continuity. One tests one connection to ground, one goes from connection to connection, and one goes connection to high output side of the distributor. Now it makes me nervous that it fails all three, but tried them six ways from Sunday and I get nothing. I checked my grounds, I checked my meter.

EDIT: Scratch the above paragraph. I retested. Make sure I'm not doing something stupid here.

Here's the illustration for the coil test. My ohmmeter is set at 200. Test 1: no reading. Test 2: 0.06. Test 3: no reading.

So it looks like I may need a coil. Sounds good enough to me.

Now, given what I've read that coils like to take ignition modules down with them, I pulled the new ignition module (less than 300 miles). It does indeed look brand new, there's a proper schmoo or dielectric grease on the bottom and it's an OEM GM part. Since my Haynes manual says special equipment is required to test the ignition module, should I (a) go to a dealer and have them test it, (b) try my luck and reinstall this one or (c) get a new GM module to be safe? I have to say, I don't like (c) because I don't like throwing parts at a problem.

Question 3: should I dig in further to check the pickup coil? One hand I'm kinda halfway there, on the other hand...well it would save me some work to not go in if I don't have to.

What say the experts?

Also, any idea how to check the crank position sensor on this truck? The Haynes manual only tells me where to find it, which is better than nothing, I guess...

The "CPS" is the pickup coil inside the distributor on these. Not uncommon at that age to have gone bad.

Oh hell, you're right. I was looking at info for '96 on. Thanks for catching me.

Everything else I've covered seem kosher here?

aLSO, the part's stores have testers to test ign coils.

In reply to Bobzilla:

I was just about to say that. They can usually test the ignition module too.

that's what I meant instead of coil.... damn fast fingers.

Well I reinstalled the old/new ignition module, swapped out the coil and it fired right up. Although both the new and old coils tested very similarly, so I'm still not fully convinced that's it. But, I have a new pickup coil ready to go in if this problem pops up again.