87 TBI starting problems

[p7387]

hello:

87 305 TBI
engine cranks but does not start

i have already checked and eliminated the obvious.......
installed new cap/rotor
installed new fuel filter
fuel pump & relay are ok, i disconnected fuel supply to the TBI and see a healthy flow coming out while cranking, additionally i see spray from the jets clearly injecting. these are visual observations only, as the flows look good i have not hooked up a fuel pressure gauge.

i tested for spark at the coil with an inline spark tester, the light flickers and illuminates, HOWEVER when i use the same
inline spark tester at one of the plugs the light is only 20% of the intensity i see at the coil directly. could this weaker spark be indication of a bad coil? and could the weak spark be significant enough to prevent firing (even if its just a sputter)

i originally started this post under electrical thinking it was a fuel pump problem, but figured it would be better placed here

thanks

[VileZambonie]

Do you have a test light?

[p7387]

the only tester/light i used was the basic in line spark tester i got at pep boys.

since my last post i changed the coil and still no positive result......
with no other options coming to mind i sprayed starting fluid into the TB and heard only a very lame sputter, in frustration i started pumping the gas pedal and finally managed to coax it to start, but it was definitely a hard forced start not a natural start, let it run for about 10 minutes, running rather smoky with a lot of CO smell. while it was running i could clearly see the injectors spraying fuel. shut it off, let it rest for about 20 minutes and attempted another start but no start, it was like i never did anything.

on the ignition side
new cap,rotor,coil and positive result for spark at the coil and at one plug i checked
(could it be the coil wire??)

on the fuel side
new fuel filter
i clearly hear the fuel pump motor/relay click
clearly saw fuel coming from the supply when i disconnected it from the TB
clearly see spray from the jets in it 2 sec prime

**note - the only thing i have not done is check for fuel pressure:
is it possible that even though i see what looks to be a healthy fuel stream from the TB supply and clearly see spray from the jets that a low fuel pressure could still be the cause of all this grief ?? i replaced the fuel pump only two years ago

when i disconnected the fuel supply from the TB i barely had enough room to move the fuel supply line away from the TB itself, any tips on maneuvering for the fuel pressure gauge, or is it better to check it at the fuel filter?

thanks

[p7387]

this keeps getting stranger...
friday was the first chance i had to spend time on the truck, so it had been sitting since sunday (5 days)
got in turned the key and it immediately started strong within barely even 2 cranks. ran great for the first few minuets and than i could see it started to gradually run rougher with the presence of heavy CO smoke. i tried to put it in gear and it stalled immediately reverting back to the same old crank but no start issue, not even a sputter. However this time i noticed if i held the gas completely down to the floor without pumping, it would make a "shuttering" rough attempt to start, but ultimately nothing-same crank but no start.

since it ran for about 10 minutes i checked for codes, only shows 12 (normal) and 15(coolant sensor)

i checked all the perimeter hoses at the tbi, the egr, pcv, etc and they all look good, and i see no apparent hose /vacuum problem
took out the pcv and cleaned it, seems ok (it rattles). was not able to check out the EGR but it looks original

i pulled 3 plugs at random, 2 were heavily coated with soft sooty carbon deposits with a dry black appearance, one was heavily coated with wet crusty deposits. all 3 did have spark, the quality seemed ok?

got all your information from my fuel pressure gauge post
thanks

[VileZambonie]

Get a 12 volt test light. Do you have a digital volt meter?

[p7387]

yes, i purchased a basic 12v test light and basic multimeter

[rsandusky]

Let's get started....Lol

Code 15 is set when the ecm receives a signal of -38 degrees from the engine coolant temp sensor for more than 3 sec while running.  Disconnect the ECT and check the resistance between the two terminals of the sensor. Insure that wiring and connector are in good condition. Post back with the results and temperature at the time of the test.

If the CTS has failed and is reading that low of a temperature the ecm will add too much fuel and possibly flood the engine. Holding the pedal to the floor while cranking commands clear flood mode to the ecm.


Don't put the meter away yet....

Check the resistance of each spark plug wire. Individually disconnect each spark plug wire and place the meter probes one on each end and record your reading. No more than 8,000 ohms per foot!!! Also, don't forget the coil wire

If you don't know how to use your multimeter let us know.

[p7387]

please, i could use instruction on the use of the multimeter

thanks

[VileZambonie]

Do a quick test. Hook your test light to ground and touch B+. Verify it lights up. Now pop the coil wire off and hold the test light about 1/4" away from the coil wire terminal. Have an assistant crank the engine. You should get a bright blue spark. Report

[p7387]

thanks for that info.

i replaced the coil along the journey and tested it with a basic enclosed light spark tester so i know its good, however i tried testing via your method for the education and to also check spark quality. i was alone so i had to cheat, i taped the probe 1/4" away and video taped it and the spark quality was good, strong blue (just curious, if i had a helper could i have gotten zapped holding the tester as my body would have been leaning on/touching the fender?)

i tried the resistance exercise on the old temp sensor and the coil wire but as i am not proficient with meter use i think i was doing it wrong. i tried various ohm settings and kept getting readings that were jumping all over the place eventually settling down to zero

so based on the code 15 i replaced the coolant sensor and That Seemed To Have Solved The Problem !!!!
i learned a lot along the way.  -  thanks for all the help.