L98 Won't Start
Drifting
Joined: Nov 2009
Posts: 1,341
Likes: 2
From: Perth Western Australia
St. Jude Donor '10
The pulses from the distributor (according to the FSM) are on the purple and white wire at the HEI module next to the distributor. The signal to fire the plugs from the ecm comes back on the white wire to the HEI module. One should be able to detect these pulses with a voltmeter set to measure about 5V DC. I have never done this test myself (never needed to) so that is about as much as I can help you with.
Race Director
Joined: Aug 2000
Posts: 11,470
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I just checked it and it seems to be connected if I'm looking at the correct switch. It is behind the distributor to the right(driver side). I did see another device that is not connected, it is a round black device with white wires that sits right at the back of the valve cover on the driver side. What is this and does it need to be connected? I see one connector that it seems to connect to down by the oil pressure switch but I don't see where the other side should be connected.
update - it took some digging, but it looks like you have an 84 with an 86 engine. not sure if we're mixing apples and oranges here, but, make sure everything is connected.
Last edited by Joe C; Sep 4, 2011 at 11:06 AM.
Thread Starter
Instructor
Joined: May 2011
Posts: 213
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From: Miramar Florida
I'm not sure if I'm looking at the correct item for the pressure switch or not but let me describe what I see. At the back of the engine just below the distributor on the driver side, I see a fitting that is screw into the engine. On that fitting there seems to be two ports, one for the pressure switch and the other is coonected to a second device that looks very similar to a fuel filter but also appears to be some kind of sensor or switch as it has wires connected to it also. I tried to attach a picture in this posting but I couldn't. Am I looking at the correct thing?
Race Director
Joined: Aug 2000
Posts: 11,470
Likes: 763
I'm not sure if I'm looking at the correct item for the pressure switch or not but let me describe what I see. At the back of the engine just below the distributor on the driver side, I see a fitting that is screw into the engine. On that fitting there seems to be two ports, one for the pressure switch and the other is coonected to a second device that looks very similar to a fuel filter but also appears to be some kind of sensor or switch as it has wires connected to it also. I tried to attach a picture in this posting but I couldn't. Am I looking at the correct thing?
Burning Brakes
Joined: May 2011
Posts: 838
Likes: 2
From: Louisville Ky
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Thread Starter
Instructor
Joined: May 2011
Posts: 213
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From: Miramar Florida
I don't recal the dash tach going up when I tried to crank it, I did notice that the oil pressure was giving a reading as high as 30. Is there anything that I can jump out electrically to isolate the problem. It doesn't seem to be the oil pressure switch. I tried to find fuel pressure guage at my local parts store but they didn't have one. When I pressed the schrader valve at the fuel rail I go fuel that shot out so I assume the pressure is good. If the pressure is not good enough will that keep the injectors from spraying?
Burning Brakes
Joined: May 2011
Posts: 838
Likes: 2
From: Louisville Ky
I don't recal the dash tach going up when I tried to crank it, I did notice that the oil pressure was giving a reading as high as 30. Is there anything that I can jump out electrically to isolate the problem. It doesn't seem to be the oil pressure switch. I tried to find fuel pressure guage at my local parts store but they didn't have one. When I pressed the schrader valve at the fuel rail I go fuel that shot out so I assume the pressure is good. If the pressure is not good enough will that keep the injectors from spraying?
the things I mentioned about isolating injector banks in case one wire was shorted or an inj is, is a simple way to discover more info.
you can ohm each injector, which is one of the first things to do. if one is shorted you will find it.
if you have fuel in the rails at 10-20 lbs, it should start.
someone may have a quicker solution.
Burning Brakes
Joined: May 2011
Posts: 838
Likes: 2
From: Louisville Ky
this is a let question, but do you have fsm? have you checked injector harnesses with test light, etc? I recall you said you were not getting pulses to injectors.
if you fsm you can go thru this test on chart a-3, 6e3 a 18.
if you don't have, the next step is to check for spark. if yes, you check one harness connector per bank with test light.
also, your c4 has ecm codes? any codes set?
***air bag fuse must be in circuit. unhook maf plug until it starts..
Last edited by joe paco; Sep 4, 2011 at 05:28 PM. Reason: ass***
Thread Starter
Instructor
Joined: May 2011
Posts: 213
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From: Miramar Florida
Finally, got the injectors firing! Found that the wire to the coil and tach were loose at the distributor. However now I am getting gas to the cylinder, it's still not starting. I can hear it firing through the exhaust, but I'm getting some blow back through the throttle body though. Seems to be just mechanics now. Any new suggestions.
Burning Brakes
Joined: May 2011
Posts: 838
Likes: 2
From: Louisville Ky
Finally, got the injectors firing! Found that the wire to the coil and tach were loose at the distributor. However now I am getting gas to the cylinder, it's still not starting. I can hear it firing through the exhaust, but I'm getting some blow back through the throttle body though. Seems to be just mechanics now. Any new suggestions.
we spent 20 posts on oil switch -by the way, was it connected?
ignition timing, probably. the problem with all posts is that only the OP knows what has been done. I assume you followed procedure to reinstall it, time it, etc? # 1 on TDC [B]compression]
if its firing in intake or x manifold the plug fires when valve is open -of course. plug wire connected wrong, one or more. oil, fingerprints etc inside dist cap, on and on. timing retarted.
maybe you can list some things you did to the dist. or maybe someone has some ideas. sounds like the path is clearer.
Thread Starter
Instructor
Joined: May 2011
Posts: 213
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From: Miramar Florida
Thanks for all the help. The reason I missed what you said earlier about the tach was because there are two sets of wires that connects to the distributor at that same point. After reading your post, I saw the set of wires connected and thought everthing was right. Later when I asked about the loose white wires that was when I realized the other set of terminals. Right now I think my issue is timing. I'm done for today and thanks for all the help. I will work on it again tomorrow if you are available to check my post. Thanks again.
Burning Brakes
Joined: May 2011
Posts: 838
Likes: 2
From: Louisville Ky
Thanks for all the help. The reason I missed what you said earlier about the tach was because there are two sets of wires that connects to the distributor at that same point. After reading your post, I saw the set of wires connected and thought everthing was right. Later when I asked about the loose white wires that was when I realized the other set of terminals. Right now I think my issue is timing. I'm done for today and thanks for all the help. I will work on it again tomorrow if you are available to check my post. Thanks again.
was it unplugged? doesn't matter, either. I stand by my FSm on that one! backup only.
thanks for the entertainment!
saludos, joe
Burning Brakes
Joined: May 2011
Posts: 838
Likes: 2
From: Louisville Ky
small town, comfortable, historic, some fine people and a few soreheads. sort of like "Our Town," without the music by Aaron Copland. still a country flavor here. a fair amount of Vettes.
nice meeting you, so to speak. now I have to be nicer, I reckon.
Burning Brakes
Joined: May 2011
Posts: 838
Likes: 2
From: Louisville Ky
my 91 fsm shows the 458 ckt from the oil switch splicing into the 458 from the pump relay. parallel to the relay, not instead of. the fsm says it is "backup" in case the relay fails.
if the FP relay failed, the engine would require more crank time, a ccouple seconds, but would run. would also run normal if relay was ok and oil switch was out of the circuit.
the oil switch does not signal ecm to fire injectors -in spite of the bulletin written many years back and still in use. not on the 91. not sure what earlier models had.
the engine needs reference pulses from dist, not oil pressure signal, the way I understand it.
joe