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Crank No Start, think a Fuel Issue, 93 3vze Pickup
Would appreciate some of you all's thoughts on the issue before just throwing parts at the problem. Have done some research through the FSM manual as well, and my thoughts on that below as well...
Went to start my truck the other day, and while it cranked fine, it refused to start. Pushed gas pedal, cranked a half dozen times of varying lengths, tried it in both park and neutral (auto trans), etc.
Went back at it today to dig in. I had no reason to suspect ignition as it sounded like it was firing, so I tried jumping the diagnostic connector at +B and FP to check fuel pressure -- and that's the easiest to check solo.
Turned key on, jumped fuel pump at DC, and heard fuel pumping.
Tried to start, and it started.
Removed jumper and the truck died w/in 30 seconds or so (didn't time exactly).
Tried to restart by just turning the key, and it wouldn't start.
Jumped B+ and FP again, and it started with a couple cranks.
I left the jumper in and let it run until the engine was at operating temp.
Removed jumper once engine was hot, and it continued to run for a good 15 minutes or so, until I turned the key off.
After turning truck off, I tested startup w/o the jumper, and it started and ran for another five minutes when hot before I turned it off by key again.
Do note, that this is just a test of one iteration of above. Will have time to go through it some more this weekend and see if it repeats.
On background:
-I usually have no issues with cold starts, starts right up.
-I get the weird hot/warm low idle issue when engine is hot where occasionally the RPMs drop really low unless given gas for a minute or so.
-Have had some weird weather her in Central Texas recently that corresponded w/ between previous start of this issue w/ swings of 40-50 degrees in one day (low 40s at night to high 80s during day), that possibly could have somehow caused a depressurizing of fuel line...
-Both today when I tried start and the day before were highs of 70s and 80s during the day; certainly at least in the 60s when trying to start this past evening.
-Battery and starter both replaced/rebuilt w/in the past two years and less than 10k miles on them.
-Had all valves adjusted 20-25k miles or so ago
-Recent Redline fuel injector cleaner.
-Plugs only have about 30k mi on them and are platinums; NGK blue wires and new distributor have less than 25k miles on them; AFAIK original ignition coil and igniter however...
-No signs or symptoms of any headgasket/compression issues though I haven't done any compression testing.
The solution:
-Based on temps and issue at hand, it doesn't appear to be w/ the cold start injector. Even if not working, it should still not result in a no start given temps
-From what I can tell, the cold start injector time switch only controls the CSI, so shouldn't be an issue.
-That led me to the fuel pump section of the FSM.
-From the wiring diagram, I'm thinking it's probably the Circuit Opening Relay which from my research on the interwebs appears to have two separate protocols for both (EDITED in quotes) "startup and standard operation -- not certain if it is related to temps or just ignition key position", if temps then this would most likely explain the issue. Again, assuming my understanding of the two separate settings is correct.
-VAFM doesn't really make sense to me, nor do the EFI or Starter Relays.
So what do you all think? Is it the Circuit Opening Relay? Is there anything else I'm missing and should check?
Thanks in advance for you thoughts!
First, check the VAF. Use your multimeter and look for continuity between FC and E1. Check that there is continuity between FC and E1 when the engine cranks. You can also check by removing the air filter and reach your finger up into the VAF and move the flapper with your finger. Make sure there is continuity between FC and E1 when you move the flapper.
If that test passes, check that the COR contact switch is closing when the engine cranks. The easiest way to check that is to look for + battery voltage at the FP terminal of the diagnostic connector when the engine is cranking. If your VAF test passes, but you do not get + battery voltage at the FP terminal when the engine is cranking, you have a bad COR (or a wiring issue).
Last edited by rustypigeon; 02-10-2017 at 05:36 AM.
Reason: added pretty pictures
I would suspect the fuel pump. I just recently went through exactly the same thing with my '88 4X4. One day I went to the grocery store and when I went to start it up, it refused to fire up. Had it towed home and started running through the tests. Jumping FP and B+ terminals allowed the fuel pump to run but instead of pulling the jumper out, I pulled the COR and checked it with multi meter. I put the COR back in and the truck fired right up. Without the jumper. I started the truck five different times to make sure it was okay thinking it may have been dirty, corroded COR contacts. The next day I went out again and the truck refused to start in a parking lot. Had it towed home again. This time, I jumped the FP and B+ terminals and the fuel pump would not run at all. I put a new fuel pump in and have not had a problem since. This is kind of a windy story but the point is, sometimes the fuel pump can be erratic in operation before it gives up the ghost. I strongly recommend doing ALL of the diagnostic testing before throwing parts at it. That can be spendy.
The fuel pump is original at nearly 180k miles AFAIK and is on my replacement list for the upcoming 180k service so I suppose I might as well go ahead and replace that. Timewise, I'd prefer not to do so immediately unless it's certain to be the issue however.
Will also check the COR and AFM. Won't have time to remove glovebox until the weekend to check the COR.
Thanks all -- with a newborn at home (our first), trying to help the mrs as we figure out this parenting thing and let various non-essential projects sit, so definitely appreciate the guidance on the most efficient approach.
If I am reading RSR's description of the problem correctly, the truck always runs with the FP and B+ jumped, and only has problems when the jumper is removed. With this being the case, I would not suspect the fuel pump.
Won't have time to remove glovebox until the weekend to check the COR.
You don't need to remove the glovebox or even touch the COR to verify that the COR contact switch is closing. The 2 steps I showed above can be completed in less than 5 minutes.
I'm with rustypigeon. My guess is the flap in the VAF is "sticky," so that once the engine is running for a while it eventually gets pulled open. Carefully hook up your multimeter as described and gently move the flap. Or, there is a hole in the flap, delaying its opening when the engine starts, so that it doesn't open quickly enough to hold the COR closed when the key is released.
DO avoid the temptation to just drive around with the jumper in. It's a safety issue; if you get in an accident that breaks a fuel line, you do NOT want the fuel pump to keep pumping.
Was on the road all day today, and got back this evening after dark. Tried again to start the truck, procedure as follows.
Tried to start the truck from cold 3 times of varying crank lengths. Didn't start.
Jumped the FP and B+ per my one attempt yesterday w/ key turned to ON prior to starting. Tried to start a couple more times. It did not start.
Checked the exhaust tailpipe and gave a sniff. Definitely smell gasoline coming from the tailpipe, so at least some fuel is coming through the system when cranking.
So since dark, I pulled the wire from the ignition coil to distributor and put against a ground where I could see from cab when cranking. I saw no spark or arching, which I'm assuming I should have seen. Tried this against two separate ground points.
If I am reading RSR's description of the problem correctly, the truck always runs with the FP and B+ jumped, and only has problems when the jumper is removed. With this being the case, I would not suspect the fuel pump.
Sorry if wasn't clear. I only tried this test once. Truck didn't start one day; didn't have time to address. Had a bit of time yesterday early so tried to quickly see if I could go through what was happening. This evening I had a few moments after getting home late where I wanted to repeat yesterday's test -- and I got different results.
You don't need to remove the glovebox or even touch the COR to verify that the COR contact switch is closing. The 2 steps I showed above can be completed in less than 5 minutes.
I didn't look to closely at your graphic -- yes, that makes sense from your graphic. I was going off the FSM procedure for testing the COR (MFI System, COR section) in which you have to remove it to test continuity and also connect various posts to battery voltage to test function as well...
I'm with rustypigeon. My guess is the flap in the VAF is "sticky," so that once the engine is running for a while it eventually gets pulled open. Carefully hook up your multimeter as described and gently move the flap. Or, there is a hole in the flap, delaying its opening when the engine starts, so that it doesn't open quickly enough to hold the COR closed when the key is released.
DO avoid the temptation to just drive around with the jumper in. It's a safety issue; if you get in an accident that breaks a fuel line, you do NOT want the fuel pump to keep pumping.
For a "lazy" test could I just disconnect the intake tube at the throttle?
For a "lazy" test could I just disconnect the intake tube at the throttle?
Sure, but we know in advance that it won't start.
You have a fuel-injected engine. The ECU controls the open time of the injectors based on the amount of air going through ... the VAF. If you disconnect the intake tube at the throttle, no air goes through the VAF, and the engine CANNOT run.
More importantly, the fuel pump won't run (once you let go of the key) because there is no air through the VAF.
You have a fuel-injected engine. The ECU controls the open time of the injectors based on the amount of air going through ... the VAF. If you disconnect the intake tube at the throttle, no air goes through the VAF, and the engine CANNOT run.
More importantly, the fuel pump won't run (once you let go of the key) because there is no air through the VAF.
Ha, whoops -- exhaustion caused brain fart (2 week old newborn mentioned earlier in thread)... Completely blanked on the built in air bypass (recalled when reading your post) and the balance of the system loop that your post is referencing... For whatever reason, I thought the VAFM meter flap might be impeding air flow w/ the remove intake elbow note... smh.
Finally had a bit of time this evening. Still a little stumped.
Tried to start again from cold a few times. Wouldn't start.
Tried jumping the B+ and FP and attempting to start. Wouldn't start again.
Smelled tailpipe and smelled like gasoline.
Then proceeded with diagnostic work.
Double checked all the ignition and ECM fuses and also looked at them closely for corrosion, etc. Everything seemed in order.
Proceeded to the ignition tests. Caveat is I'm a relative novice w/ multimeters and not entirely confident...
Distributor tested out good and like new for all -- got 173 ohm resistance at 2,000 ohm setting on multimeter for 3 tests; spec is 125-200 ohms for all.
Ignition coil I'm not certain about the readings. Primary coil test at 200 ohm setting on multimeter, I got a 0.90 ohm reading w/ cold spec at 0.36-0.55 ohm (hot is 0.45-0.65 ohm). So this is high. Secondary coil reading w/ multimeter at 2,000 ohm setting (both positive and negative posts read same; FSM specifies just the + terminal) was 11.82 ohms with cold spec at 9.0-15.4 k ohms and hot spec at 11.4 to 18.1 k ohms.
So my assumption here is that the cold #s are what I should use, and probably that primary coil test was nearly double spec suggests that might be a reason for weak spark due to greater resistance, if weak spark is the culprit... Thoughts here?
And this concluded the ignition testing I did.
I also tested the VAFM.
VS - E2 tested at 311 ohms w/ multimeter at 2,000 ohm setting w/ spec at 200-600 ohms.
VC - E2 tested at 282 ohms w/ multimeter at 2,000 ohm setting w/ spec at 200-400 ohms.
THA - E2 tested at 3.40 ohms (presumably converted to 3,400 ohms due to setting) w/ multimeter at 20,000 ohm setting w/ spec at 2-3k ohms for 68* F and 4-7k ohms for 32*F. Temp was approx 55-60*F at the time of testing, so between 32 and 68*F ranges...
FC - E1 tested at 1 ohms, which is presumably infinity as standard reading when testing probes not in use. Spec is infinity.
I did not have time to disassemble air box this evening to test terminals w/ moving measuring plate..
I had read elsewhere (when holding baby so mrs can sleep have gotten some research and reading done) about some folks having success w/ disconnecting vafm connector. So I tried to start my truck with the vafm connector disconnected.
It started and ran for 5 seconds or so. Tried again, and same result -- running for 5 seconds before dying.
I plugged the VAFM sensor back in and tried restarting again. The truck then started and ran for 20 minutes or so. I turned off once warm and waited 30 seconds or so and it restarted as well w/o issue. I also walked away for five minutes or so after turning truck off. I came back and again it restarted while warm.
So today has 3 possible things I'm thinking might be the cause:
-The ignition coil
-Something w/ VAFM
-Something possibly w/ the fuel (tank at 1/4 full, and gas no more than 2 weeks old at this point, one week old when restarting, and standard shell fuel)... Thought on fuel is that the truck doesn't start the first time but after letting it sit and trying again in an hour or two time it seems to start up so possibly a little fuel evaporation is making it easier for truck to start than just turning key... Suppose might also relate to a weak spark...
Looked at all wires and connectors for VAFM and ignition stuff, and noticed no corrosion, etc, of concern.
I also did not have time to check the FP diagnostic connector w/ test light on startup...
Would appreciate the YT resident expert opinion as always. And thanks in advance.
Would appreciate the YT resident expert opinion as always. And thanks in advance.
My opinion remains unchanged. I don't proclaim to be the YT resident expert however. Your symptoms point to a malfunctioning VAF or COR.
-Do you have continuity at VAF terminals E1-FC when the engine is cranking? You NEED to know this. I posted a picture of the VAF connector so you could identify where the FC and E1 terminals were.
-Do you have battery voltage at the FP terminal in the diagnostic connector when the engine is cranking? You NEED to know this. I posted a picture of the circuit and even used my limited artistic ability to draw a picture of how to hook up your multimeter for both tests.
The results of the above tests will tell you what direction you need to go in the diagnosis, that is why I asked you to check that first. Have a helper crank the engine while you check those two items. It is extremely simple, takes 2 minutes and gives you very valuable information. If the above tests show no faults, then it is time to check other things like ignition, fuel pump, wiring to fuel pump etc.
Last edited by rustypigeon; 02-17-2017 at 11:54 AM.
2nd, follow rustypigeons early posts on checking the VAFM and report your findings. When you unplug the VAFM the car should start and die righ away, 5 seconds is even too long. So if it started and died as you said, this is pointing towards the VAFM and/or the components that it relies on for signals.
rustypigeon, RSR said he checked the E1-FC circuit and the reading was essentially no resistance, so it has continuity.
rustypigeon, RSR said he checked the E1-FC circuit and the reading was essentially no resistance, so it has continuity.
He said it read "1" which some multimeters use to show "overlimit", which would mean infinity.
Regardless, FC-E1 should only show continuity when the engine is running, cranking or the flap if manually moved with a finger. It should show infinite resistance when the engine is shut off which is how I assume RSR checked it.
He said it read "1" which some multimeters use to show "overlimit", which would mean infinity.
Regardless, FC-E1 should only show continuity when the engine is running, cranking or the flap if manually moved with a finger. It should show infinite resistance when the engine is shut off which is how I assume RSR checked it.
You are right, my new multimeter does that actually
02-09-2017, 09:00 PM
