I got this 87 K5 that's giving me some starting issues and I cant seem to figure it out. I just bought it drove about 200 miles and had no issues. After about a 2hr drive I noticed it started surging on me and wanted to die out at idle. I parked it and did not drive it for a couple days, I then fired it back up and notice it would run for a couple minutes and start surging or pulsing at idle once again. I reved it up, drove away and didn't seem to have the issue again. After another couple days I went for a drive with no problems and then all the sudden when I gave it gas it started to bog out and wanted to die. The only way I could get the truck to move was by pumping the gas peddle over and over. Now it starts and shut right back off At this point there has been a service engine light which through a code 44. Ive tried some different things but no luck, I changed out fuel filter map sensor and IAC, it seems like its getting plenty of fuel, injectors spray evenly ive tried unplugging 02 sensor and vacuum lines but no difference on anything, one thing I did notice was that when I unplug the Map Sensor the truck starts right up and runs for about 10 seconds and dies, when I plug it back in it takes a few attempts. Also I can get it started and keep it running with idle at a happy medium but no more no less it dies, could it be the TPS sensor or EGR Valve please any suggestions I feel its something easy I'm just missing it. Thanks
CK5
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1987 Chevy K5 Starting Issue!
- Thread starter Big V
- Start date
I'd try disconnecting the EGR valve, and manually moving it with your fingers on the underside. If it gets stuck open, it is a vacuum leak. EGR is essentially a "cruise" only deal, often you'll see EGR issues manifest themselves once the vehicle has warmed up and driven steady-state, like highway.
Don't throw parts at it, the O2 sensor is telling you it's lean http://www.misterfixit.com/code44.htm
Don't throw parts at it, the O2 sensor is telling you it's lean http://www.misterfixit.com/code44.htm
just because the injectors are visually spraying, doesn't mean there is enough fuel pressure to keep it running. if I remember right it needs to be 14-16PSI
I think I'd start with checking all vacuum hoses then block off the brake servo hose and start it again. If it's still bad, spray a solvent or light oil (Easy Start, carb cleaner, WD40, that sort of thing) around the throttle body base gasket, inlet gaskets, EGR gasket etc to check for air leaks, just listen for a change in engine pitch. Pumping the gas peddle isn't going to help you on a TBI motor as there is no pumper. If you have no air leaks check your fuel pressure. As dyeager535 says, don't throw parts at it. That's a really expensive way of tracing a problem!
Actually pumping the pedal does help. With a carb, opening the throttle causes an increase in air into the engine, plus a drop in manifold vacuum which is what caused the fuel to flow.
The result is a sudden extreme lean condition.
Thus you have the accelerator pump that squirts a shot of gas in to counteract that lean condition.
With EFI, the fuel delivery is caused by the injectors, so manifold vacuum does not affect the amount of fuel delivered. But, that does not change the fact that you are suddenly dumping a lot more air into the system with no increase in gas. Of course, as soon as the oxygen sensor sees the lean condition, the computer will compensate.
But, until then, the engine is stumbling.
Thus the Throttle Position Sensor. Not only does it tell the computer where the throttle is, it also tells the computer when it moves, which way, and how fast.
So, when you suddenly open the throttle, the computer changes the injector pulses to shoot more gas in.
As Benny Hill used to say, "Lot of People Don't Know That".........
So, if pumping the throttle makes it run better, then its usually a lean problem. Which makes the EGR a better suspect.
The result is a sudden extreme lean condition.
Thus you have the accelerator pump that squirts a shot of gas in to counteract that lean condition.
With EFI, the fuel delivery is caused by the injectors, so manifold vacuum does not affect the amount of fuel delivered. But, that does not change the fact that you are suddenly dumping a lot more air into the system with no increase in gas. Of course, as soon as the oxygen sensor sees the lean condition, the computer will compensate.
But, until then, the engine is stumbling.
Thus the Throttle Position Sensor. Not only does it tell the computer where the throttle is, it also tells the computer when it moves, which way, and how fast.
So, when you suddenly open the throttle, the computer changes the injector pulses to shoot more gas in.
As Benny Hill used to say, "Lot of People Don't Know That".........
So, if pumping the throttle makes it run better, then its usually a lean problem. Which makes the EGR a better suspect.
OK I wasn't aware of that, I assumed the ecu would only deliver as much fuel as needed (engine speed, load, TP etc) but I was actually referring to trying to start a reluctant motor the old 'carb' way of pumping the pedal to throw a lot of gas down the hole, which of course you can't do with TBI while the engine's not running. ( as far as I know! :-) )
True, pumping with the engine off only increases your left leg muscle mass........
I read his post to say that the engine was running but bogging down and about to stall and pumping helped. I may have read it wrong.
I read his post to say that the engine was running but bogging down and about to stall and pumping helped. I may have read it wrong.
Have the CTS (coolant temp sensor) on top of the intake tested to see what it's telling the computer (you will need to run a data stream). If the CTS is telling the computer it's 33 below (which is what usually happens when it's bad). The ECM will dump fuel in the engine and flood it out. Pumping while starting sends it into (clear flood mode) (shuts off fuel injection) and can allow it to start.
Best advice I can offer, STOP SHOTGUNNING. Get someone to read the data stream so you know exactly what's happening. It will save you money in the long run. I am not a professional mechanic but, I have learned over the years that $500 bucks is $500 bucks whether I do it a little at a time and get lucky or I just pay someone to fix it because I don't have a computer to read the damn thing.
Best advice I can offer, STOP SHOTGUNNING. Get someone to read the data stream so you know exactly what's happening. It will save you money in the long run. I am not a professional mechanic but, I have learned over the years that $500 bucks is $500 bucks whether I do it a little at a time and get lucky or I just pay someone to fix it because I don't have a computer to read the damn thing.
chulisohombre
1/2 ton status
I had this same problem a couple years ago. It was the fuel pump. Everything looked ok but would start and run a minute until it his closed loop and then would die. Test the fuel pump. Should be between 9-14 psi. Any lower than 9 and it can't run correctly. Mine was at 6 and was barely enough to keep idle going.
Usually the transient enrichment is a combination of "pump shot" based on TPS and "tip in" read by the MAP sensor. When these are tuned right, the O2 won't get a lean condition (it's more likely to be rich on the transient actually). This is good because the physical travel of exhaust gasses makes the O2 reading too late to compensate. The O2 is for trimming during somewhat steady-state conditions.
The lean conditions point to a vacuum leak (EGR being one possible source) or possibly a fueling problem.
whiskeyfist666
Registered Member
Had this same problem years back. If my memory serves me well I believe my problem was the Ignition Module
