92 Bravada 4.3l w-code no start problem

Last week, my wife's Bravada (4.3L Vortec, W-Code, 125k miles) died on me, but thanks to AF, I determined that the CPI was the most likely cause of the problem. The car had all the symptoms: Over a period of a few weeks, it went from running and starting fine to having to hit the key three or so times prior to it starting, to having to hit the key countless times before it may or may not start. It had plenty of fuel making it to the rear of the plenum, and all kinds of spark, etc.

So, with the assistance of some really fantastic pictorials here on AF, I decided to swap that bad boy out. Sure enough, the regulator side of the plenum was completely washed. I swapped out the CPI and Nut Kit, buttoned everything up, then cranked her over. After the car fired up, and after waiting for the crap to burn off that was fouling the plugs, I took her for a test drive. Everything seemed fine. It started right up when cold, and even seemed to be running better than it had in about 6 months.

Until yesterday. When I got home from work, the wife told me that she had to crank the engine a couple of times before it started, both before going to work in the morning as well as before coming home in the evening. Then this morning, it failed to start at all.

Any ideas of what I may have missed? I freely admit that I am a Ford guy myself, and a pre-computer Ford guy at that, and I know that there is a bunch of stuff on these new(ish) engines that I just don't fully understand. But it still seems to me that if there is fuel flow and spark, there should be a running car (or at least a car that seems to be TRYING to start, but I only hear and feel the starter winding away.) I think I must be missing some obvious check here, but I'm fresh out of ideas.

Speaking of missing something, but on a completely different issue, I decided after "fixing" the CPI problem to check the initial timing on this Vortec, but for the life of me, I cannot locate the timing marks or plate, which should of course be somewhere down near the damper on the crank (at least, that's where they were on every other vehicle I've worked on.) Did GM do away with the timing marks all together, or am I just blind? I know that the advance timing is all computer monitored and controlled, but I figured that the initial timing would at least still be adjustable. At the very least, I would think the timing marks and plate would still be on the engine somewhere, if for no other reason than for finding TDC during a major engine overhaul. Any ideas where these timing marks might be hidden?

Thanks in advance for any suggestions. I hope my status as a non-GM guy doesn't dissuade any one from helping!

Last week, my wife's Bravada (4.3L Vortec, W-Code, 125k miles) died on me, but thanks to AF, I determined that the CPI was the most likely cause of the problem. The car had all the symptoms: Over a period of a few weeks, it went from running and starting fine to having to hit the key three or so times prior to it starting, to having to hit the key countless times before it may or may not start. It had plenty of fuel making it to the rear of the plenum, and all kinds of spark, etc.

So, with the assistance of some really fantastic pictorials here on AF, I decided to swap that bad boy out. Sure enough, the regulator side of the plenum was completely washed. I swapped out the CPI and Nut Kit, buttoned everything up, then cranked her over. After the car fired up, and after waiting for the crap to burn off that was fouling the plugs, I took her for a test drive. Everything seemed fine. It started right up when cold, and even seemed to be running better than it had in about 6 months.

Until yesterday. When I got home from work, the wife told me that she had to crank the engine a couple of times before it started, both before going to work in the morning as well as before coming home in the evening. Then this morning, it failed to start at all.

Any ideas of what I may have missed? I freely admit that I am a Ford guy myself, and a pre-computer Ford guy at that, and I know that there is a bunch of stuff on these new(ish) engines that I just don't fully understand. But it still seems to me that if there is fuel flow and spark, there should be a running car (or at least a car that seems to be TRYING to start, but I only hear and feel the starter winding away.) I think I must be missing some obvious check here, but I'm fresh out of ideas.

Speaking of missing something, but on a completely different issue, I decided after "fixing" the CPI problem to check the initial timing on this Vortec, but for the life of me, I cannot locate the timing marks or plate, which should of course be somewhere down near the damper on the crank (at least, that's where they were on every other vehicle I've worked on.) Did GM do away with the timing marks all together, or am I just blind? I know that the advance timing is all computer monitored and controlled, but I figured that the initial timing would at least still be adjustable. At the very least, I would think the timing marks and plate would still be on the engine somewhere, if for no other reason than for finding TDC during a major engine overhaul. Any ideas where these timing marks might be hidden?

Thanks in advance for any suggestions. I hope my status as a non-GM guy doesn't dissuade any one from helping!

You need to get a fuel pressure gauge on it and see if fuel pressure is up to specs and holds pressure with out a fast leak down.
Did you check the nut kit for leaks when you replaced the injector?
The two plastic feed lines inside intake that feeds the injector unit?
Post back fuel pressure and if any fast leak down.
If good fuel pressure and good spark check egr valve for carbon under pintel valve.


Timing marks may be behind water pump on upper side of timing chain cover.
But to base time you have to unplug the timing connector wire.

Fuel pressure before I changed the CPI dropped fast. After the change, it was holding at 58psi for twenty minutes (which is all I left it on there for.) But it was a borrowed guage, and don't know how it would read now.

Nut Kit was changed at same time as CPI. I had pressurized the system prior to reinstalling the upper plenum to verify no leaks, and everything seemed to be seated properly without leakage.

I'll check the EGR on Sunday (I have to work all day tomorrow.) But I'm still a little concerted as to why such similar symptoms would develop all of a week after the initial repair. I did have some trouble getting the middle poppet on the right side seated, the one that doesn't really clear the fuel line until it's all the way down. I wonder how the engine would respond if in fact it wasn't seated all the way down and worked it's way up somehow?

I'll look again for those timing marks. On the bottom side of the engine bay there is a plastic shroud to protect the fan and front of the engine from rocks and debris. Do you think they might be on the bottomside of the damper?

I'll let you know how I make out, probably early next week.

Thanks again.

Good reason to recheck the fuel pressure.
It will tell you if still a fuel pressure problem or other wise.
Let us know how it goes.
MT

So, th epressure starts out at about 51 psi, then falls off over a few minutes to about 44 psi. Say about an eight or nine minute time frame. So, I think I have a leak.

I guess it's time to go tear the plenum off again, but I don't know what could have loosened up. But I'll check everything out, try to see where the leak is coming from. I just hope I don't have to replace anything again. Pocket are only so deep, you know?

Thanks for the help; I'll keep you posted.

Well, GM has managed to confuse me once again. I removed the upper plenum, but did not see any obvious signs of leakage. In fact, everything seemed pretty dry. When I pressurized the system by turning the key to "On", I still didn't observe any leaks.

So, I decided to simulate parking the car for the night by leaving it alone for about 8 hours (more than enough time to watch the Bristol race!) I figured that this would give the system time enough to lose pretty much all of its pressure. I had my wife turn the key to "On" while I watched under the hood. No leaks. I even pulled the coil wire and had her crank the car over. Again, no leaks.

I know that the initial fuel pressure was a bit on the low side with the key "On" engine "off", about 51 psi. I think I read in my Hayne's that it should be between 54 and 64 psi. Might this be the cause of my current problem? I figure that I'll throw a new fuel cap on tomorrow, but I don't know how GM pressurizes the system, so it may not make any difference. (I don't know if the fuel system maintains it's pressure via a one-way style valve in the fuel pump itself, or if the whole system, tank included, is pressurized. If it's the former then the new cap won't matter.)

Does anyone know what sort of fuel pressure loss rate I should expect if I leave the tester on the line for a few hours, starting from it's initial fully pressurized pressure (key "on" engine "off")?

Mine drops 5 to 6 lbs. over a 20 minute period. Do you have fire to the sparkplugs?

Mine drops a bit faster, about a 10 psi or so drop over the same time frame. Of course, mine is also starting out at too low a pressure (about 50 psi). After an hour, it's down to about 35 psi, after 2 hours it's down to high 20's in psi.

Spark is great on all plugs. Fairly new rotor, cap wires and plugs.

Turns out, I can in fact get the car to start cold. I just have to crank it a heck of a lot. Once it's warm, it runs fine. There may be a very slight hesitation when you jump on the gas pedal compared to pre-CPI change, but it's so minimal that I can't tell if it's real or if I'm imagining it.

I've pretty much narrowed down where my current problem (insufficient fuel pressure) must be coming from. It has to be one of three things: 1) A leak in the fuel system; 2) A clogged fuel filter; or 3) A weak or leaking fuel pump. I've thoroughly checked the fuel lines from the CPI on back to the tank, and there are no leaks. I've replaced the fuel filter, and the pressure remains exactly the same. So, the only thing left is the fuel pump. Either it is simply weak (which for a car with 144k, wouldn't be too surprising) or the check-valve is failing to hold the fuel in the line. With my rate of pressure loss, I'm betting on the later.

So, once I run out as much fuel as I can, I'll drop the tank and toss a new pump into the mix. I figure it will probably be done Thursday (the next time I know that I can sneak out of work a little early.) But I'll keep you posted.

Thanks, MT and Chris, for all your help. I will let you know if I'm successful or merely covered in gasoline.

PS Does anyone know why it seems to be hit or miss with posting? I swear, I've had to write just about everyone of my posts at least twice. I'm sure that I log in prior to actually attempting to post anything, but it almost always brings up the page informing me that I either did not log in or am unauthorized to do so. What am I missing here?

I know what you mean with the posts...if I have a long post, I'll highlight the text and right click "copy" to save it on the desktop before I post a question or reply in case the site equipment is too busy.

Problem solved. Turns out the fuel sending unit was shot. I had planned to just replace the pump itself (about $60), but the whole assembly was so completely rusted over that I went ahead and replaced the whole thing (about $200). More than I wanted to spend, but what else is new?

So now the fuel pressure stays a steady 61 psi for several minutes, and only really drops 4 or 5 pounds in half and hour or so. The Bravada starts and runs fine, now.

Thanks for all the help. It's just my luck that I would have two major fuel problems at the same time on the same vehicle. Although I wonder now if a small piece of rusted metal from the sending unit may have been sent through the lines to the injectors, causing one of them to spring a leak.

Again, Thanks! And sorry it took so long to update you folks. I've had a string of sh**ty luck with all my vehicles recently after this repair, and just didn't get the time until now.

You are welcome and.
Thanks for posting back with the fix and letting us know how it went.
Glad all is well witt it.
No way metal from tank can get to injectors.
Filters and screens keep it out of them.
But be sure to check you inline fuel filter.
Good Luck
MT