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Joelsstuff
Active Member
13 Posts |
 Posted - 08/25/2010 : 06:11:38 AM
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Hi, I just purchased a School Bus, 1991 Chevrolet with a TBI 366. It last ran about 3 months ago and now will not start or even show a promise of starting. Here is what I know and have done so far: By listening and upon turning key on, fuel pump would run for a few seconds and then quit. Removed fuel pump and tested in a bucket - again, it ran for a few seconds and quit - very little fuel pumped. Measured input voltage to pump at 8 volts. Hooked pump directly to 12 volt source and it ran without stopping and pumped fuel very well. Put pump back into tank and kept seperate 12 volt supply to pump - engine would not hit at all.
Checked fire to plugs and engine is not firing. Do I have multiple problems here or is this a computer issue? What can I test next to help narrow this problem?
Thanks for your help,
Joel |
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bwest
Administrator
United States
3820 Posts |
Posted - 08/25/2010 : 06:50:20 AM
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| The first thing I would investigate is your voltage problem. A low battery can cause all sorts of problems |
Bryan |
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Joelsstuff
Active Member
13 Posts |
Posted - 08/25/2010 : 10:45:41 AM
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Battery is showing between 12V and 13V. Engine spins over with no problem. How about the fuel pump relay? Also, where do I find the fuel pump relay? I would expect to find it in a fuse box but I haven't found it yet?
Thanks again!
Joel |
Edited by - Joelsstuff on 08/25/2010 10:47:39 AM |
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78fordwayne
Top Member
USA
2868 Posts |
Posted - 08/25/2010 : 11:02:32 AM
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You stated above that your fuel pump will run for a few seconds when the key is turned on.
That means your relay is working fine.
Your problem is ignition related , not fuel since you have no spark. |
Robert B.
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Edited by - 78fordwayne on 08/25/2010 11:03:50 AM |
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baptistbusman1
Senior Member
USA
175 Posts |
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Joelsstuff
Active Member
13 Posts |
Posted - 08/25/2010 : 2:41:19 PM
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Baptistbusman, you sound fairly confident that the ignition module is the problem. I'm ready to go and buy this part but I'm sure it would be non-returnable. Are there any other symptoms or simple checks that I can look at to eliminate other possible causes? It sounds like this might be a "same song, second verse" type of problem.
Thank you very much,
Joel |
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baptistbusman1
Senior Member
USA
175 Posts |
Posted - 08/25/2010 : 3:08:48 PM
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well, pull the cap and see what is in there. Probably lots blue corrosion looking stuff. You can actually take that module off and take it to an oreillys store or possibly an autozone and they can check it for you. But the thing is, I have had bad modules before, and when checked they come back saying they are still good.
In reality though, in all my years dealing with 366's, 99% of the non start issues I have ever encountered was a bad ignition module. |
I was formally Baptistbusman. However, I lost my password, and had not updated my email address.
Here is a link to my old posts. http://www.schoolbusfleet.com/forum/search.asp?mode=DoIt&MEMBER_ID=1846 |
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BJ Henderson
Advanced Member
USA
280 Posts |
Posted - 08/25/2010 : 5:11:29 PM
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| You can check it very easy for module failure. With a 12 volt test light, see if the coil is being triggered. Also, check to see if you have a good ground at the coil. Get back to us. Tell us what you find. |
CMTT,CMAT,CMBT |
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Joelsstuff
Active Member
13 Posts |
Posted - 08/26/2010 : 1:54:27 PM
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Here is what I've found: There are two pairs of wires at the coil. None of these wires has 12 volts with the ignition turned on. One of the wires has about 1 volt with ignition on and then dead with ignition off. I can't tell much about the coil being grounded. So, it looks like there's a problem with getting hot to the coil. Now, back to the fuel pump issue. It seems to me that I've still got separate problem with low voltage to the fuel pump. Now, I'm wondering if there is a single electrical problem causing both of these symptoms. Remember, the battery is hot and the engine spins like I think it should.
Thanks again for your help,
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Joelsstuff
Active Member
13 Posts |
Posted - 08/30/2010 : 1:09:54 PM
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I've been trying to find a wiring diagram to see where the coil is supposed to get its power. The wires disappear into a harness and into the firewall, making it difficult to trace. Any thoughts as to why I'm not getting 12V to the coil when the ignition is turned on? Or, advice on where to look next? I'm probably a day or two away from getting a wiring diagram.
Thanks |
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Wolf0r
Top Member
USA
2181 Posts |
Posted - 08/31/2010 : 1:33:45 PM
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| There is an ignition coil fuse in the box under the dash. Very bottom fuse. Also check to make sure the fuse box is getting 12v to all the fuses and not just one bank. The stud outside on the firewall under the master cylinder is where most of the fusible links connect. Do the injectors spray at all? |
“The good thing about science is that it's true whether or not you believe in it.”
Neil deGrasse Tyson |
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Joelsstuff
Active Member
13 Posts |
Posted - 09/03/2010 : 1:49:02 PM
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Sorry, I've been away for a couple days - I will check per your instructions. I'm going to say that the injectors are not spraying because the fuel pump is still not running. I found a blue and yellow wire along side each other in the engine compartment that looked like they ought to be connected together. With these connected, the coil now has 11 volts but no fire on plugs. I'll get back with you - Thanks again,
Joel |
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BJ Henderson
Advanced Member
USA
280 Posts |
Posted - 09/05/2010 : 05:48:19 AM
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Did you find your blown fuse? 10 amp? Joel, what it sounds like is that you have a voltage drop somewhere. Either there is a corrosion problem, a heated up wire connector or both. If modules do not get enough voltage when cranking the engine over, they will not fire the coil(s) or the injectors. I would check for fusable links or a voltage drop through them. I would start at the starter connecton. I would also check the ignition switch. Joel, do you know how to do a voltage drop test?
Remember, SAFTEY FIRST when poking around the starter connections, since you are bypassing all saftey devices intended to keep you safe. I say this because someone else might read it and get hurt. Plus, I have my name and location available, so I would be easy to find. Maybe it is time to put a disclaimer in my signature on my profile... |
CMTT,CMAT,CMBT |
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Joelsstuff
Active Member
13 Posts |
Posted - 09/07/2010 : 12:35:31 PM
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I have not found any blown fuses and I think you are correct in that there is a voltage drop somwhere. I'm no electrical expert but I believe that a voltage drop will ultimately create heat somewhere and that is what I need to be looking for. I suppose that there are a couple ways to measure voltage drop? Place the leads of my meter across (on each side) a suspicious point and determine resistance, or measure voltage on each side and look at difference in potential. I know of no better place to start than at the battery and starter. I wish that I had a wiring diagram of this (1991 Chevy C60)but have yet to find one on the net. Thanks again and I'll report back my findings.
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BJ Henderson
Advanced Member
USA
280 Posts |
Posted - 09/07/2010 : 7:19:34 PM
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Since you now have voltage to the coil, take your test light and use it to find a ground on the coil, if I remember right, it is the white wire, keep in mind that most electronic modules control ground sides of circuits to keep the voltage from blowing transistors inside of ECMs (electronic control module, or PCM, powertrain control module).
Take your test light ground clamp, put it on 12volts and have someone spin the engine and see if you get the light to flash when testing the coil. If the test light flashes real fast, you know the module is working inside of the distributor. If it does not flash, you have distributor problems, either your crank position sensor, if it has one, or pole piece on the distributor shaft, or module inside the distributor, as someone else has already suggested.
Test this and get back to us. |
CMTT,CMAT,CMBT |
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Joelsstuff
Active Member
13 Posts |
Posted - 09/07/2010 : 8:51:35 PM
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I failed to add to my previous post that I had removed the distributor cap and then removed the ignition module. I noticed white corrosion material on what looked to be metallic mating surfaces. I removed this stuff on both the distributor and module and then took the module for testing. It tested (by three different methods) to be functioning properly, so I re-installed it. I will check for ground at the coil next - my wires are white and red.
Thanks again,
Joel |
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BJ Henderson
Advanced Member
USA
280 Posts |
Posted - 09/08/2010 : 03:46:54 AM
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The white stuff on the bottom of the module is heat sink compound, hope you installed something to help the heat have a path out of that module, dilectric grease works well for that.
On the bottom of that distributor rotor, if you see any black smokey looking stains on it, replace it. I would suggest AC Delco or from a Chev dealer, even better. It is cost effective insurance to replace it as it transfers up to 40 kilovolts DC current. If there is any other path to ground inside that distributor cap that has less resistance than the sparkplug wires and sparkplugs under compression, the cranking voltage will go to ground inside that distributor cap.
Joel, in testing for ground circuits, just hook your test light ground clamp up to battery voltage and then use the sharp pointy end to look for the ground. The white wire on the coil should be grounded by the module with the engine cranking. You will see the test light flashing very fast.
Also keep in mind that there must be roughly 9 volts to the coil with ENGINE CRANKING for the plugs to fire.
I would also pull that battery, as someone else already suggested, and take it to a local independant automotive shop and have them check it. Charge it before you take it, that should save you and them some time if the have only the old type carbon pile tester. Remember, a weak battery kills starters.
Test these things and get back to us. |
CMTT,CMAT,CMBT |
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Joelsstuff
Active Member
13 Posts |
Posted - 10/04/2010 : 2:49:02 PM
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| I have had more time recently to look at this and here is where I'm at. I found a poor connection on the ignition wire at the wire plug just behind the fuse block. Now, the engine will fire and even run if I pour gas into the TBI. TBI injectors aren't squirting at all. I loosened fuel supply line at the TBI and had fuel to the TBI. I loosened the recirculating line from TBI and no fuel is recirculating back to tank. I believe that this tells me that my fuel pump is not putting up the needed pressure to open the spring-loaded diaphragm at the TBI. My plan is to buy a new fuel pump. I'll report back with my findings. Thanks again! |
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BJ Henderson
Advanced Member
USA
280 Posts |
Posted - 10/04/2010 : 6:26:59 PM
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| I would check for fuel filter restriction, first. You are going to want to install a new fuel filter anyway if you put a new fuel pump on it. One bad tank of fuel can restrict a fuel filter. |
CMTT,CMAT,CMBT |
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Wolf0r
Top Member
USA
2181 Posts |
Posted - 10/08/2010 : 06:16:57 AM
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| I recently had to put a pump in a Thomas on a GMCV. The hole wasn't cut in the right place in the floor, and a brace was directly over the sender. Sawzall to the rescue. |
“The good thing about science is that it's true whether or not you believe in it.”
Neil deGrasse Tyson |
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Joelsstuff
Active Member
13 Posts |
Posted - 10/14/2010 : 04:50:40 AM
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I have good news to report. My bus is up and running! I bought a new fuel pump and after bleeding air out where the feed line enters the TBI, she started right up and runs like a top. The only issue I have right now is trying to understand why I have only about 7.5 volts going to the fuel pump. Right now, I'm running the fuel pump with another battery to get 12 volts. The fuse and surrounding area looks good but I haven't yet found the fuel pump relay and I'm losing the wires as they go into a big loom. In the end, I guess I can wire around this problem using a switch but it would be nice to have it all working. I very much appreciate the support and input and thank God my access plate was in the right spot!
Thanks again,
Joel |
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Wolf0r
Top Member
USA
2181 Posts |
Posted - 10/14/2010 : 06:22:07 AM
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| Joel, check for the relay on the firewall. Usually on the right side next to the starter relay. |
“The good thing about science is that it's true whether or not you believe in it.”
Neil deGrasse Tyson |
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Joelsstuff
Active Member
13 Posts |
Posted - 10/14/2010 : 08:44:26 AM
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| I was looking under the dash and listening for a click. I'll check the firewall. |
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BJ Henderson
Advanced Member
USA
280 Posts |
Posted - 10/14/2010 : 4:51:18 PM
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Joel, check where the fuel pump wiring goes through the plate that screws to the top of the fuel tank and see if the wiring and connections look good there. This connection is known to give problems. Some aftermarket fuel pumps come with connections and instructions on the repair.
If you try to run the bus with that low voltage to the fuel pump, it will make the new pump fail in a short time.
Did you find the fuel filter? |
CMTT,CMAT,CMBT |
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Joelsstuff
Active Member
13 Posts |
Posted - 10/18/2010 : 11:57:51 AM
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Yep, I found the fuel filter - NAPA brand and it looked new like someone had recently tried this. I'm getting plenty of fuel flow through it and the bus is running well but the pump is hooked up to another 12V battery sitting in the floor. I want to check the hot lead against battery ground to ensure that I don't have a grounding issue that is causing the 7.5 volt reading. Partial voltage would suggest that something has to be heating up a bit somewhere doesn't it?
Thank you very much,
Joel |
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BJ Henderson
Advanced Member
USA
280 Posts |
Posted - 10/20/2010 : 6:29:25 PM
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Yes, Joel. That circuit runs from starter, through ign switch, to fuelpump relay for 3 second run on, then through the oil pressure switch with engine running.
The ECM controls the ground side of the fuel pump relay.
Now, to do your voltage drop test, turn your voltmeter to 20 volt reading, measure voltage drops, with the circuit under load (turned on) on the positive wires, across all points where you might have heat buildup. When you see a voltmeter reading across that heat buildup, it will be the amount of voltage loss you are getting.
Less than 1.0 volt is ok. If you see 6.0 volts it is a 6 volt loss due to bad contacts in relay, corrosion problems,bad switch or whatever.
You put the red and black voltmeter wires on the circuit, loaded. I know it sounds nutty, but try it.
Then tell us what you find. |
CMTT,CMAT,CMBT |
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Joelsstuff
Active Member
13 Posts |
Posted - 10/21/2010 : 04:40:00 AM
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BJ, thanks again for your help. I do understand the concept of measuring the voltage drop on two hot wires. It may not be this week, but I'll get you an answer.
Joel |
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Topic |
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91 Chevy 366 not starting
