Truck cranks, but won't turn over after sitting for a week

[Eric M.]

Got a problem and need some help!
87 V3500, 454, fuel injected.

If I don't drive my truck for a week or so, it won't start up. It'll crank just fine, but no fuel is pulsating from the injectors. It use to be that I could jump it and it would start right up. I can turn it off right after it fires and it'll start up just fine again. I thought the battery voltage was low preventing the computer from sending a signal to the injectors and that was why it would fire up after jumping. The last time it happened, I bought a new battery and it started right up. I changed altinators thinking that was the issue.

Now here I am, with the same problem. This time, jumping wasn't enough, I ended up using a plug in battery charger / starter while jumping and it still took a while to fire. I'm thinking it may not be a voltage issue.

Any ideas what whould prevent a signal being sent to the injectors after a truck sat for a while? And why does it cure itself right after (at least for a few days)?

NOTE: Truck has 2 tanks,I have switched tanks while this was happening. Same problem with both fuel pumps ... I havn't checked the ful pump relays, kind of thought the worked or didn't, no intermitent stuff with relays.

Thanks,

Eric M.

 

[slyguy_22]

Had a very similar problem with my 406tbi blazer. double check the wire that runs from the back of the alt. to the battery and make sure its not broken or loose. the end on mine was broken at the back of the alt so it would let the engine turnover but wouldnt power the fuel pump. replaced the end and was fine.

 

[dyeager535]

First off, you need to see if you are getting an injector pulse. (need to make a tester with a bulb, unless you already have one)

Just because there is no fuel, doesn't mean you aren't getting an injector pulse...

Spark and fuel are needed for an engine to run, *everything* else is a waste of time if you don't have both. Since you obviously have spark, that only leaves fuel.

 

[habitatxskate]

some things, the ground, clean terminals/grounds, and especially (was my problem as well) THE CONNECTORS!

 

[4X4HIGH]

I suspect a bad fuel pump relay. The truck will still start with a bad relay but it will take more cranking so the oil pressure sensor (for the fuel pump) see's oil pressure before the pump will start pumping.

 

[Eric M.]

A few updates.
There is fuel, I pulled the line while cranking and it's under pressure. The fuel pumps are working (see above) and I can hear them buzzing in the tank when the ignition is on. I'll try to check the injectors for a signal, I know need to wait a week for this to happen again! Anyone know what sort of voltage I should expect at the injectors?

Thanks,

Eric

 

[dyeager535]

You don't measure voltage, you need a test light to check that the ECM is grounding the leads. The injectors will (should) have the same voltage as your fuse panel.

Well, I better slow down. You can test voltage at the injectors, but that only tells you that they are getting voltage, which is all the time with key on. Bulb test tells you both.

 

[readymix]

Dorian is correct. He helped me through the same crap a few years ago.

Remember that on lead of each injector will be a steady +12Vdc, the other lead will be grounded by the ECM causing the injectors to fire.

It really is a simple system to troubleshoot once you understand how it works.

 

[stoneagemaxx]

a similar problem was my buddies '92 w/a tbi 305 the computer went bad and for some reason when it sat for 3+ days and tried starting it cold it wouldent start or took a long time and you had to depress the throttle sometimes, changed the computer and it has been fine since, 2 and a half years, it may not be the problem but something to think about if you can get a spare ecm to put in

 

[Eric M.]

The Fix

Checked voltage between pos. connection at fuel injector and ground, got 8 volts when cranking starter. Checked same voltage on another truck and got 10 volts. Checked all my positive connections from the battery forward in electrical system. Found battery cable at starter end was nothing but crusty rust. Replaced cable and all is good once again.

Eric M.