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73-87 Chevy _ GMC Trucks => 73-87 Chevy & GMC Trucks => Topic started by: beavo on September 13, 2010, 11:22:40 pm
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???i have an 87 tbi that up and quit the other day it backfired once or twice then quit i figured it was the fuel pump as it would not start off the key but prime it and it would run until it burnt the prime i changed the pump the brand new pump wouldnt run put another in it now it pumps fuel but truck still will not run it has pressure up to the tbi i checked that the injectors have fire i checked that and with it running as long as you keep pouring gas down it i guess that means all the ign is good please help as i am at a loss thanks.?.
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Had a Lumina van once that had similar sounding issue. It turned out to be a bad ignition module??
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ok thanks for the help ill try that
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wouldn't a bad ignition module cause it to not have spark? Checking for spark should tell ya if that is good, i believe. But, you have spark because when you pour gas in it starts.
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well thats what i thought to that the module was good cause of it running but i just had it tested and of course it was good i also took the ecm out and put it in a van that my father owns and it runs like a top so now im back to square 1
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What is it reading for fuel pressure? Did you look at the injectors with a timing light to check the pattern?
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it doesnt have a place to check the pressure and no i didnt check it with a light because there is no fuel out of the injectors at all and to make sure i placed a paper under the injector and had my wife crank it and there was no fuel on the paper thanks
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My van died, I got it home thinking fuel pump. Sprayed some gas out of a squirt bottle into the throtle body it fired right up. Did that several times. Was dark so next day I decided to investigate a little more. Sprayed gas in, and it wouldn't run. Checked for spark had none.
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Check for injector pulse. Use a noid light or 12v test light. Unplug one injector connector, key on engine off, test light to ground probe both terminals one should illuminate the test light. If ok put test light to B+ and touch the other terminal which did not illumiate (the ground side of the injector harness) have an assistant crank the engine - observe your test light. It should blink. -Report
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do you have a vats not sure what years they started in wana say newer than ours but not sure? if not beavo it might be a pain but swap out distributors with thee one in your dads van. pick up coil sends a signal to the icm the engine is turning to fire the injectors icm then sends the signal to the ecm. you tested the icm and ecm but not the first step the pick up coil just something to think about. also the oil sending unit tells the ecm when it senses 4psi to turn on the injectors might be another parts swap while you’re under the hood
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ok so i had tried making sure that the injectors were gettin fire by running the test with the light before i made this but not to make sure it pulsed the b+ your talkin about where is that and for the oil press i have a gauge in the truck and it shows some where around 18lb when cranking but that doesnt mean that the press switch is bad tho does it is there any other way to check the pickup coil and as for swapping the dist id like to make that a last resort and with many future days of frustration i may go ahead and do it lol but anyways thanks for all the help yall i really appreciate it
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check to ensure your spark plugs are getting spark. Take one plug out. Put the plug wire on that loose plug. Hold the plug tip up against the metal engine...block, head or some place that will ground out the plug tip (that's what happens when the plug is in it's correct postion--it grounds via the threads in the head). Have someone crank the engine--but, hold the plug with a rag so as not to shock you through the plug wire.
You should see a spark jump accross the gap of the spark plug if you keep it held against the metal engine.
If not spark, it could be pick up coil or not getting volts out of distributor.
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ok so i had tried making sure that the injectors were gettin fire by running the test with the light before i made this but not to make sure it pulsed the b+ your talkin about
So are you saying you performed the test I described? Yes or No? If you did what are the results? You need to check the injector driver circuit.
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i did do the test you are talking about i did it before i started asking for help on here i took my test light turned the key on took off my injector wires and checked the wures with the light one of them was hot with the key on when i had my wife crank it i tried the other wire cause the one that was hot with just the key on didnt pulse the other wire did nothing no pulse no nothing but i was asking about the b+ you mentioned whats that because i am now not sure if i did exactly what you are talking about and also what or where is the driver circut htanks again
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B+ means battery positive. B- means battery negative. So if you have your test light connected to B- anything that is B+ will illuminate your test light that you probe. If you have your test light hooked to B+ anything that is grounded will illuminate your test light that you probe.
If you verified B+ at the injector harness but didn't verify the injector driver circuit by checking for the presence of ground with your test light then you need to do that.
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If the injector turns out good then to test the pick-up coil, first disconnect the white and green module leads. Set the ohmmeter on the high scale and connect it between a ground and either the white or green lead. Any resistance measurement less than infinity requires replacement of the pick-up coil. I'm kind of doubtful of it being bad but just one less thing that it could be. By time you take the distributor apart you can swap it out with another
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ok guys finally got time to work on my truck i changed the dist for one that i know is good and ran the test with my light hooked to the b+ and i have no pulse coming through that wire so once again back to square one thanks again
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Circuit Description :
This chart assumes that battery condition and engine cranking speed are OK, and there is adequate fuel in the tank. This chart should be used on engines using the Model 220 throttle body.
Test Description : Numbers below refer to circled numbers on the diagnostic chart.
A "Service Engine Soon" light "ON" is a basic test to determine if there is a 12 volt supply and ignition 12 volts to ECM. No ALDL may be due to an ECM problem and CHART A-2 will diagnose the ECM. If TPS is over 2.5 volts the engine may be in the clear flood mode which will cause starting problems. If coolant sensor is below -30~C, the ECM will provide fuel for this extremely cold temperature which will severely flood the engine.
Voltage at the spark plug is checked using Spark Tester tool ST 125 (J26792) or equivalent. No spark indicates a basic ignition problem.
While cranking engine there should be no fuel spray with injectors disconnected. Replace an injector if it sprays fuel or drips like a leaking water faucet.
Use an injector test light like BT8320, or equivalent, to test each injector circuit. A blinking light indicates the ECM is controlling the injectors.
This test will determine if there is fuel pressure at the injectors and that the injectors are operating.
Diagnostic Aids :
If no trouble is found in the fuel pump circuit or ignition system and the cause of a "Engine Cranks But Will Not Run" has not been found, check for:
Fouled spark plugs
EGR valve stuck open
Low fuel pressure. See CHART A-6.
Water or foreign material in the fuel system.
A grounded CKT 423 (EST) may cause a "No Start" or a "Start then Stall" condition.
Basic engine problem.CHART A-4 - INJECTOR CIRCUIT DIAGNOSIS
(http://i6.photobucket.com/albums/y228/Sabaka454/Schematics%20and%20Diagrams/A-31.gif)
Circuit Description :
This chart should only be used if diagnosis in CHART A-3 indicated an injector circuit problem. If both injector circuits fail to blink when tested, diagnose, one injector circuit at a time.
Test Description : Step numbers refer to step numbers on diagnostic chart.
This step tests for 12 volts to the injector. It will also determine if there is a short to voltage on the ECM side of the circuit.
This test checks for continuity to the ECM.
(http://i6.photobucket.com/albums/y228/Sabaka454/Schematics%20and%20Diagrams/A-3.gif)
(http://i6.photobucket.com/albums/y228/Sabaka454/Schematics%20and%20Diagrams/a3.gif)
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i done the test that the chart instructed i hooked to a ground and probed my ecm plug in 16 and 14 they both lit up so i hooked to B+ and ran the test on the other side of the plug 16 lit bright and 14 was very dim is this a symptom also the chart says the ecm or the connections are faulty but i had already tried my ecm on my dads van and it run and the connections in both the ecm and the plug look good so im still at a loss thanks again yall
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So test light to ground key on engine off both injectors have B+? Test light to B+ other terminal no blink when cranking? If this is correct then you have lost the injector driver. Go directly to the cavity on the ECM Either D14 or D16 and backprobe it there. If you have the driver there then you have an open circuit.
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so i checked the d14 d16 in the ecm plug with my light and it lit well on both of them so i hooked my light to the hot on the batt. and checked the other side of the plug as i assumed that the other side was a ground and one lit well and the other was real dim does this mean anything thanks again
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D14 or D16 is being backprobed. Do not unplug the connector. Use a paper clip to make contact with the terminal (don't jam it in there) Hook your test light to B+ and the paper clip -then crank the engine. Do not hook the test light to ground this won't validate what you're looking for. It should cause your test light to blink while cranking. Depending on your test light it may be a dim blink so look carefully.
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sorry it has takin me so long to get back on here but i checked the ecm like you said i cant see a blink it only slightly dims when you crank but no flash so please tell me what to do know cause im completely lost thanks again
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OK start over since it's been a while. Test light to B+ touch ground, test light illuminates. (yes) take test light and backprobe cavity D14 or D16 with a paperclip and test light should blink while cranking the engine. Report
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Yes correct this is what i done no blink. Light does dim slightly of course when cranking but no flash. Thanks Again.
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And you have good spark?
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if you mean spark on the plugs i havent visually checked it since when you prime it with gas it runs so i thought it was ok
thanks again