QuestionThanks for the response Van.
A)I do not have a deterrent systems, this is a factory correct 1988 Chevy truck. (other than when I bought it it ran)
B)During compression testing with all plugs removed there was some mist coming from the #7 cylinder (I electrically disconected the solenoids at the throttle body while preforming compression test to stop fuel flow). Why the #7 I have no idea but none of the other cylinders. At that point I thought of water in the gas even though I had just filled up the tank 5 days prior. To keep this semi short after pulling 2 quarts of fuel out from the delivery side fuel line (via fuel pump) and letting sit for many hours there was no seperation. So I put the contents of the container in my pressure whasher and ran it...it worked fine. The analysis then was it is fuel. You are correct however in that I did not check for proper fuel pressure.
I have dumped known good fuel down the throttle body throat(s) with no success. When I tell people that they want to know about compression and I checked all cylinders, #6 low @ 100 psi (not good, bad valve since about 30K miles) but all the others are 150 psi to 160 psi. I have used AMSOIL in this motor since 36K, & filters and regular changes.
C)I did know about the relationship between #1 and #6 cylinders, however thanks for the tip about that relationship and the intake and exhaust valves, I had not thought that through.
THIS IS PORBABLY THE ONLY IMPORTANT QUESTION.
D)The 3 amp fuse, ppl/wht wire, at the ECM but pink at ignition switch, is still my biggest concern. There is no easy way to test this for continuity because the access to both ends (ignition switch and ECM) is virtually impossible to get to.
I am speaking of the wire from the ignition switch pin "C" which starts out as a pink wire.
So if there is any verification or explaination of what that wire does it would help.
Note: I believe the distributor reference pulse is from HEI ignition module, under the distributor cap, to ECM pin B5 is that true? No reference pulse, would that make it not run/start? That module has died on me before during normal driving conditions. I Replaced module and the truck has been doing fine for 30K (about).
My book shows a wire from the ignition switch at pin C through a 3A fuse (and note that says) "To Engine Control Module" no indication of what pin at the ECM.
E)Thanks for the advice on the timing chain slack measurement. Thank god I have no more questions there.
F) As discribed above, I did pull plugs and turm motor over.
G) I will certainly take the time to measure vacuum but how well can I tell what vacuum there is without it running? Is stater RPM enough? I suspect this is O.K. however because it was running fine the last time it actually was running.
Thanks kindly for your advise. I do take it seriously. I am not a mechanic (obviously) but do enjoy the work on my own cars. However I have never been this baffled since I was 16 years old. Do you recomend a better service mannual and if so which one? Again thanks.
I promise I will not write back.
Followup To
Question -
My question is...are there any remote modules that can keep my 1988 3/4 ton 5.7 350 Scotsdale from firing (ie starting).
I have spent $500.00 on modules replacements (bad way to trouble shoot I know). I have good spark (3/4")I have fuel and throttle body solenoids seem to be fine (I can see fuel being delivered but did not check volume)engine was timed with timing light(by running the starter)
This is a HEI system of course. Did not disconect "Timing wire coming from harness" because I can not find it. With valve cover off, both #1 valves (Intake and Exhaust) are relaxed ie closed. This is informational for timing set-up of course.
No reports from ALDL (other than code 12), but if I pull electrical connector from a sensor it does report that sensor (I suggest this is a fair test of ECM functionality/handshake).
Is there a "Roll over shut-off switch" or other simular device on that year/make. I assume this is not the problem because I have spark/fuel/compression and lets just assume correct timing for now.
Comment is I had the distributor out to replace parts I am confident that it is reinstalled correctly but before pulling the distributor I had not checked to see if the timing chain had jumped a tooth or more. This could give a false impression of correct ignition vrs cam vrs crank timing if I am not mistaken (meaning I could have set the ignition timing to be firing when the #1 piston was not at TDC I am thinking). That will be my next effort meaning the verification of #1 at TDC ect. This is the only thing I can think of that has a remote possibility of still being bad so I am at a loss for any advice.
In my CHILTON manual (#8055 pg. 6-68) in the electrical schematic section I see a 3 amp fuse coming off of the ignition switch pin "C"(PPL/WHT) and going to the ECM, I can not find this fuse. Is it in the harness or maybe in the ECM itself? The fuse box does not show any fuses under 5 amps so I figure it is not there.
I guess I should say that I have owned this truck since it was new in 1988 and it has 147K miles. It was running great when I parked it and let it sit for 5 days then went out to start it and it has not run since.
Any advice would be appreciated and thanks in advance.
Answer -
Hello Doug,
Long question here so I will try to address each in order.
I don't know of any remote modules, unless you have a theft deterrent system. But later on you say there is spark. You said 3/4...does it have the spark with the ignition in run and cranking with a jumper switch, or is it there when cranking with the key? (Thinking bad ignition switch here, so just make sure there is spark...at the plugs...when cranking with the key).
OK...spark present with key...you see fuel being delivered.
Are you SURE it is fuel? Any chance you got a slug of water in the tank? I don't mean a tablespoon...I mean a gallon. Quick check....dump a couple ounces of known good gas down the throttle body, then crank it.
You didn't mention checking the fuel pressure. You want a full 13 PSI at the throttle body, even when running under load. 12 is OK. But if you test the pressure, that is a good time to drain off about a pint in a clean pint jar. Let it sit a while, and see if a big glob of water forms at the bottom of the jar. or heaven forbid, it is straight water.
Now, that timing with the valve cover off is great. Take it a step farther. To tell if the crankshaft and camshaft are correctly timed, roll the crankshaft exactly one revolution in the normal direction, from where both #1 valves are relaxed. Just after half a rev, the exhaust valve will open. As you continue around, and are slowly bringing the timing mark up toward the pointer again, watch the rocker arms for #1.
As you come up, that exhaust valve will be closing, and at the instant the exhaust valve gets completely closed, the intake rocker will begin to open.
That is a very precise point, but you can easily see it.
At that exact point, stop and look at the timing pointer.
It should be exactly on TDC.
It is TDC of cylinder # 6, as well as # 1. They are opposite each other in the firing order, and that happens to be TDC of compression stroke of # 6, and exhaust stroke of # 1.
If the timing mark is on TDC, and assuming the rubber in the damper pulley isn't rotten and slipped, then the chain did not jump.
So if that worked right, rotate the engine one more turn to where the #1 valves are relaxed, lign up the timing mark, and then check the rotor, to see if it is pointing toward # 1's wire tower.
That 3 amp fuse could be a small fusible link. I show two purple/white wires to the ecm.
One says crank fuse, and the other says distributor refference pulse. That one is to let the ecm know it is ok to run the fuel pump. The fuel pump relay will be de-energized if the engine is not turning over. That is so if you are in a wreck, the fuel pump doesn't keep pumping gas while you are just laying there.
The crank fuse I would expect to find in the fuse block. Mine shows it as a 5 amp. I believe if you remove it, the key will not operate the starter. May only be hot in crank.
To check slack in the timing chain....rotate the engine by hand in the normal direction, with the distributor cap off.
Notice the position of the rotor. Then turn the engine backwards, very slowly, till the rotor begins to move.
If you had to turn the crankshaft more than just a few degrees, there may be excess wear in the chain and gears.
I would bet that if you took reasonably good care of the truck while you owned it, and changed the oil regularly, the rotor will start moving almost the same time as the crank.
Another test for the water, is pull a few plugs, and see if they have water on them.
Here is a final thought. Vacuum.
See if there is good vacuum. Possible causes of not having it are the egr valce stuck open, or the brake booster leaking badly.
Van
AnswerHi Doug,
Absolutely nothing wrong with Chilton manuals. I use them myself.
I just happen to have a Mitchell, but it is for a 1989. I doubt there would be a bit of difference in the wires from 88 to 89.
But I don't show a 3 amp fuse anywhere.
The pink wire from the ignition switch goes to the distributor batt terminal,which is batt for the coil.
It also operates a variety of different things, that if one works, then the switch and pink wire are good. Some of the things powered, in addition to the coil, are the injectors, backup light switch, turn signals, instrument cluster, and a few others that you may or may not have. But if there is spark, then the pink wire and ignition switch are good.
The purple and white wire going to the ECM pin C9, is the crank signal to the ecm. It comes from the ignition switch when in the crank position. It is the same as the purple wire at the starter, which engages the solenoid, with the exception that it does pass through the crank fuse in the fuse block. But its purpose is to tell the ecm that you are actually cranking the engine over with the switch, and to go ahead and allow the fuel pump to operate.
You have fuel pump running, so that wire is ok.
You have another purple and white wire going to the ecm, pin B5. That one is distributor refference, and comes from the module in the distributor. I really don't think it would have anything to do with the no-start, because I am relatively sure the ecm doesn't control the timing while starting.
I am thinking base timing may be off.
The wire you need to disconnect when checking that should run across the front of the firewall, probably inside the harness, but should be exposed in the area of the brake booster. Tan and black wire, and a connector just in line.
It could be near the drivers fender, and could also be over nearer the engine, but it will be exposed.
I will say that I heard of a guy finding his under the dash, near the heater blower on a Tahoe...seems about a 95 model, but that would be very unusual.
But I would start by ligning the timing mark, and then make sure the rotor points as close as possible toward #1, and then try moving it a few degrees in each direction.
As for that mist in #7....if it continues even long after disconnecting the fuel injectors, you might think about a leaking intake manifold gasket.
And please do write back.
richard_vannatta@sbcglobal.net
Van
