Stalled out

Okay recently,

Driveing my 98 blazer down the road and it chugs litely, no big deal I keep going.

Next day it chugs a bit more while on the interstate. At this point im starting to wounder, fuel Pump going out?

Next day at every stop the blazer wont idel I come to a stop sign and it just kills. But it starts right back up. Seems to stay running if the rpms were kept up.

Next day same thing. But I accelerate off a stop sign and the rpms are jumping up and down, I then coast off to the shoulder, and await my tow back to the shop.

I was positive it was a bad fuel pump so I switched it out with a new one.

Still nothing its not even trying to start. Dont seem to be alot of fuel pressure while cranking, I just get a little squirt out??

Check for spark and nothing?

So I tap the coil and some other things, not really knowing what im doing at this point. Try to start it and it hits and runs really rough for about 15 seconds and then shuts back down.

SO I replace coil, pickup oil, and the little computer modgule thing.

Crank it, and still no spark out of the coil and not much fuel pressure.

So I pull crank sensor, I brought it to the little garage in my town and he hooked it to a volatage meter and told me it was open. So I put it back in but still nothing.

I am pretty much stumped here. I would like to do further diagnosing. I dont much for testing equipment so bare with me on this. I got to get this back on the road soon so I just want to thank everyone in advance..

paxfam1

Heres a start:
1. Check the fuel pressure at the valve on the fuel rail - KOEO 60psi is the min to start. Fuel filter changed - if not do it (under frame rail by drivers seat.
2. Done the crank sensor and still no spark at the coil so check to see if 5v feeding the coil with key to run and voltmeter on the 2 outside pins in the coil connector (unclip it and test in the connector.
3. Could be ignition module but need a scan tool to check and they are $80.
4. Check all fuses inside and out - eng and 2 ecm ones.
5. Replace the dist cap and rotor before you go for the ign module - just had one internally arcing and no way to tell without changing - yes believe it.
6. Cam sensor does not stop stratup only idles rough so thats not it.

Fuel filter was changed but no diffrence,

I only seem to be gettting the fuel thats primed when the key it turned, after that the pump doesnt kick back on

the ignition modgule was replaced earlier but it didnt make a diffrence


I will check for the 5v tonight and post the results

Does the pump not run again for two seonds when the engine is cranked? Bump the key briefly to move the engine and listen for another two-seond pump cycle.

Well, the fuel pump is working as so.......When I turn the key it primes and when I bump it primes again then I think it must hit a sertain presssure and then when I bump it it doesnt run any more, but if I let the squirt of gas out it will work again.

As far as power goes, as far as I can tell there is no power to the coil at all, but there is power to the little ign modgule I beleive thats what it is, but I replaced that so it should be good. Should there be constant power to the coil while they key is at run and not just when its cranking??

Also I noticed the alternator was making a high pitch humming, I thought maybe something was wrong with it so I unhooked it but it still dont start.

What should I check next, shouldnt there be spark coming from the coil, even if the distibutor cap or somthing was bad, I mean I replaced the pick up coil, but seems like even if something was off time or something I could at least get it to hit once, but no.

Where do I go from here?

People, could I please get some ideas on where to go from here, I really would appreciate some help.

Thanks in advance

paxfam1

Well, the fuel pump is working as so.......When I turn the key it primes and when I bump it primes again then I think it must hit a sertain presssure and then when I bump it it doesnt run any more, but if I let the squirt of gas out it will work again.

As far as power goes, as far as I can tell there is no power to the coil at all, but there is power to the little ign modgule I beleive thats what it is, but I replaced that so it should be good. Should there be constant power to the coil while they key is at run and not just when its cranking??

Also I noticed the alternator was making a high pitch humming, I thought maybe something was wrong with it so I unhooked it but it still dont start.

What should I check next, shouldnt there be spark coming from the coil, even if the distibutor cap or somthing was bad, I mean I replaced the pick up coil, but seems like even if something was off time or something I could at least get it to hit once, but no.

Where do I go from here?

The fuel pump seems to be operating when it should, but we still don't know what the pressure might be. There has to be a minimum of 61 PSIG (I've seen them start at 58, but barely).

At this point, if I could figure our why I have no spark I would damn happy

lol I really kneed some pointers..................

Alright, I have read this one, sounds interesting. The Ignition module has been replaced, also the crank sensor has been replaced too. I have too look tomorrow for the diagnosis chart for this one. I had a similar problem like this on my '95. Turned out being the connector to the ignition module was not good, and was intermittent and caused me a lot of trouble. When checking for spark, hook up a spark plug wire and ground it to the block, don't just check for spark at the coil itself, you run a risk of damaging either the coil, or more importantly the ignition module again(happened to me and I needed to warrenty the first module I bought because I damaged it, also took me awile to firgure out I cooked the one I bought). You have to make sure the ignition module is getting the right voltage, with the key on engine off, and also while turning over the engine, same goes for the crankshaft sensor. I don't remember the correct flow chart for diagnosis, so I have to find it.

That would be good if that was the problem, the only reason I was testing for spark from the coil was to elimante any problems in the dist cap/rotor. But yea if you could get me the specs that would be great!

Just one side note, If you have a MAF on your rig (which you would on a 98) once you open the throttle body (take the rubber boot off) it will run bad untill the air intake is put back on. I had a Problem with mine it was esentially a vacume leak around the top of the boot. Mine would start NP, run like A_S. but rechecked what I had done a week before and the boot had shifted and was not locked in correctly.

No its not that, I cant even get spark it wont even attempt to start so thanks anyways!

Alright, a easy way to check if your ignition module and or crankshaft sensor is operational is when turning over the truck to start it, you should have your tach working, or if you don't have a tach, you need a scanner where you can watch live data. If the scanner shows rpm, ( 200-500 rpm), when turning it over, then at crank sensor is operational, as is the module. Also, what is the status of your battery? Does it have a sufficient charge?

It seems as if the rpms quit, when I removed the crank sensor. I had it tested and it was open so I put it back in and now it does not show the rpms going up or down. Yes the battery is charged up, also I noticed a whining noise coming out of the alternator so I unhooked it but it made no diffrence!

It seems as if the rpms quit, when I removed the crank sensor. I had it tested and it was open so I put it back in and now it does not show the rpms going up or down. Yes the battery is charged up, also I noticed a whining noise coming out of the alternator so I unhooked it but it made no diffrence!

By quitting I assume you have no tach response(it stays at "0" when you turn it over). You can't really test the sensor that way, you actually need a tester for these, or you watch for RPM output on the scanner or dash tach itself. Make sure your connections to the module and the crank sensor are tight and strong. A good way to ensure this is to slightly bend the prongs that is on the harness to one direction, very little, so they are slightly not straight. When you go to plug it in, since its not straight, it will make good contact as you snap it together. Other then that you have to check for voltage at both the module and the crankshaft sensor. I have the diagram from this, but I have to get it on here, which I will do later. It will give you and idea what to look for.

you are correct, the diagram would be good.......... hope this works thanks again

paxfam1

Heres a diagram on the ignition system.
http://aycu32.webshots.com/image/5791/2001646472829436722_th.jpg (http://allyoucanupload.webshots.com/v/2001646472829436722)

okay, now I have the diagram but what are some things I should test for, I dont really no where to start..........should I check for shorts in the harness or what do you advise me to do first.

thanks paxfam1

Alright at the ignition control module, A is positive, and should be 12 volts, and C is the ground, turn the ket to the on positon, and, using a voltmeter, probe and check to make sure you have the necessary voltage at that point.

If that checks out alright, next look at the crankshaft sensor. Wire 439 ignition is positive(or C), is positive and sould have 12 volts with key on.

You can check the crank sensor by probing the pink 439 wire and the purple 574 wire for I think its 3 volts while turning over the engine while probing. I have to check for this as I am not totally sure what the exact voltage its suppose to be, 3 or 3.5, or something, I don't remember. If there is no voltage while cranking and probing, then as long as there is voltage at the sensor(pink 439) then the crank sensor is either not connected good to the harness connector, or the sensor itself is bad.

OKay...........................Thanks for the info, I will try testing tonight or tomoro and let you know the results............Thanks again paxfam1

okay, This is what I found

Tested for power at the modgule, I could not get any power with the two outside pins so I grounded to the block and then there was power to the positive it was 12v.....so I have no ground there,

Tested at the crankshaft sensor and found 12v at the purple wire

tested the crank sensor and also found 12v, but I was not cranking cause I had no one to help me..... so I dont no if it would be 3 or what ever then or not.

Should I put a new ground to the control modgule???????

what should I do next?

Alright, here is some more information to help you diagnose the ignition system

This should hopefully help.
http://aycu16.webshots.com/image/335/2001333689403541113_th.jpg (http://allyoucanupload.webshots.com/v/2001333689403541113)

http://aycu37.webshots.com/image/3116/2001342098632839578_th.jpg (http://allyoucanupload.webshots.com/v/2001342098632839578)

Im still stuck at my last post, that was good information but it didnt help to much!


Thanks Paxfam1

[quote=paxfam1]okay, This is what I found


Should I put a new ground to the control modgule???????

[quote]

No after checking a little more, that should have 12 volts also (the opposite, two out wires/leads). That diagram doesn't look to be right, odd. Also to verify, I checked on my own '98 to make sure.

You start on level 3 of the diagnositc tree. And basicly tool J 39200 is a voltmemeter.

Ok hold on, did you replace the crankshaft sensor, I re-read your first post, and I am not sure, sounds like you didn't. Also, when you replace the ignition module, did you disconnect the battery before doing this? These modules are sensitive, and there is a big possibility you can damage it if you don't disconnect the battery before you install it, especially if the key was in the "ON" position for any reason while you were doing this.

As long as you have good connections, you have voltage at the necessary wires, and the sensors themselves are functioning properly, your good to go.


The jumpy tach is something I persoanlly had happen on mine. It ended up being the module, but the crank sensor was showing some funny things on my scanner after it started, so I went ahead and replaced the crank sensor too, and after that all was well.

No, I didnt replace the crankshaft sensor, the guy told me it was open to I just put it back in. And no the battery was hooked up when I put the new modgule in but they key was off so there shouldnt have been any juice there.

But the one thing that concerns me is the ground that I was talking about earlier. it wasnt grounding its in the connection to the mogule if I hit the outside pins I get nothing but if I hit the + and ground to the engine block then I get 12v could this ground be hooked to something else as well?????

I think I may have found the problem.............Okay I was dueing some testing and I found that wire 150 that is supposed to be a ground, is not grounding its not doing anything. so I put the ohms meter on that wire and the wire 121 wich goes to the coil itself, and its an open circut? That doesnt seem right does it, but also wire 121 from the coil is not grounding either. Any ideas????? Any chance some one knows where the ground wire 150 is hooked to the block, its appears to be towards the back side of the motor because that is about as far as I can trace it..................... It doesnt seem right to me according to the diagram...............Let me know, am I onto something or am I on something.


Thanks Paxfam1

I think I may have found the problem.............Okay I was dueing some testing and I found that wire 150 that is supposed to be a ground, is not grounding its not doing anything. so I put the ohms meter on that wire and the wire 121 wich goes to the coil itself, and its an open circut? That doesnt seem right does it, but also wire 121 from the coil is not grounding either. Any ideas????? Any chance some one knows where the ground wire 150 is hooked to the block, its appears to be towards the back side of the motor because that is about as far as I can trace it..................... It doesnt seem right to me according to the diagram...............Let me know, am I onto something or am I on something.


Thanks Paxfam1

I have been out for awhile working on my owm truck, and stuff. I just would like to know where you are at this point. Hopwfully you have progressed a little, or even got it running. I dont at this point thing ou have a wiring problem. In my opinion, I am still suspectful of that crank sensor.

No, its not running im still stuck at the last post I left the smorning, I did replace the crank sensor, it was the crankshaft sensor that wasnt replaced, it is what the mechanic called open so it should be good. I believe there is some kind of wiring problem in the wires I mentioned in the last post please please post any thoughts about the wires..................

paxfam1

No, its not running im still stuck at the last post I left the smorning, I did replace the crank sensor, it was the crankshaft sensor that wasnt replaced, it is what the mechanic called open so it should be good. I believe there is some kind of wiring problem in the wires I mentioned in the last post please please post any thoughts about the wires..................

paxfam1

I'll get some more info tomorrow and paste it up here, if no-one beats me to it. First and foremost, did you check and recheck the fuses, the ecm fuses, and the ignition fuses, all or any fuses for that matter to make sure nothing is blown?

yea I checked them awhile ago, but I will check them again tomoro............... But I didnt check any of the relays, but they shouldnt have any affect on ignition system............correct.........yea if I could get some more info that would be excellent

All fuses were good..................

its almost is if I am getting nothing from the "ignition control" I cant seem to get anything out of those wires. Then agian I had some kind of circut I was telling about earlier. Do you think some sort of controller is bad? Maybe?? what would it be and where is it?

Any comments/suggestions????????????????????????????

its almost is if I am getting nothing from the "ignition control" I cant seem to get anything out of those wires. Then agian I had some kind of circut I was telling about earlier. Do you think some sort of controller is bad? Maybe?? what would it be and where is it?

The ignition control module is located close to the actual ignition coil, on top of the engine. The module is what essentially controls ignition. The parameters, ie where timing is suppose to be, crankshaft(camshaft postion) is also found by the each of their sensors, and information is managed by the VCM, which inturn, controls injector firing, timing, etc, etc. You mention you changed the module, did you check and make sure the coil is good? When you turn the engine over, is your tach moving? I woulnd't suspect the ground wire like you mention becausee you mentioned your fuses are good. If they are good, it probably isn't a ground issue.

yes, I changed the coil itsself when I changed the modgule. The tach used to move when I turned it over, but after I had taken the crankshaft sensor out and had it tested, I reinstalled it but it doesnt move anymore. I was thinking ignition switch, but I really dont no for sure how to test that.

My shop manual says not to try to test the crankshaft sensor, because trying to test it will burn it out. I don't understand how this could be, but that's what the GM factory repair manual says.

well it read open when I had it tested, but the tach was moving before this all went down so oviosly something else is wrong........I have a feeling its something to do with the wires going to the control module/coil I tested and I gave the results in an earlier post.

I want to try and switch out the ignition switch, but hly sht theres alot of wires under there, O popped a panel off under the dash but its a maze with oput some sort of diagram.

Did you forget about my little problem, please help!

Its been awile since you last wrote on here, I thought you figured it out.

I don't think an ignition switch would cause this problem of a no start- you have to be looking at the ignition system. You have no tach as far as I understand from the previous post. No tach reading points to an ignition problem, or related components. If you still have no spark, and cannot figure it out to this point, no sense in tearing into more of the truck. I haven't has a chance to closely look at the wiring diagrams for a '98's ignition system, as that would help more, you should try to locate this and take a close look. If you cannot figure that flow chart out, the one I posted earlier for the ignition system, I suggest you find someone that can, if not, it would propably be a good idea to take it to a shop at least for diagnoses.

You have four things in this system that operate the ignition system;
1, Crank shaft sensor
2, Ignition module
3, Igition coil
4, PCM (engine computer)
and of course all related wiring and fuses.

The camshaft sensor will not cause a no start, although it is apart of the ignition system, the truck will still start, but you will have a SES light on almost right away after it starts.

Hello, New Crankshaft Sensor in today, and it started right up. Thanks for everything boys. Now I want to put new plugs in this beast, what are the best plugs to run in it?