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Runs rough, rich error, high fuel pressure

Tiny
ROBERT CURTISS
  • MEMBER
  • 1995 GMC JIMMY
  • 4.3L
  • V6
  • 4WD
  • AUTOMATIC
  • 90,000 MILES
I am working on the vehicle listed above that was sitting in a garage for two to three years.

Battery was replaced and then the fuel pump since the old one was not providing any fuel plus, once I got to it, one of the hose connections had rusted through.

It now starts, but rough. Service engine soon light blinks after a couple minutes (running rich). Liquid which seems like just water comes from the exhaust. I have not been able to get it up to temperature since I started this.

Fuel pressure was checked, after fixing a bum gauge. Using the pigtail on the side wall to run the fuel pump, I am getting 70 psi, 66 or so when running. The fuel pressure does not hold when the pump turns off. I opened up the intake and expected to find a leak but I did not. I still replaced the regulator, but not the entire spider. I crimped hoses and neither stopped the bleed down of fuel pressure, but crimping both seemed to slow it down.

No leaks seen anywhere in the fuel line. I even pulled out each injector to look for leaks, none found.

I replaced the cap, rotor and plugs, the wires look brand new.

When it runs, there is a 'tick' that is in relation to RPM (higher RPM = faster ticks).

The fuel pump was not an AC Delco, but the chain store's stock. I am not confident in the fuel pressure gauge.

I have not touched the fuel filter because the pressure is good. I know the gas is old, but seems like it shouldn't be this rough.

Ideas? I am considering the following: spider (just because it fails all the time, but I have already replaced the FPR). Maybe a faulty fuel pump? Other?
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Wednesday, August 1st, 2018 AT 2:46 PM

38 Replies

Tiny
STEVE W.
  • MECHANIC
  • 13,586 POSTS
I would try a different gauge for the pressure as it is possible yours is reading wrong, however as it leaks down fast the check valve in the pump is faulty and that will cause starting issues even if the pressure is okay. The old gas is not going to help the situation, especially if you are in an area where ethanol is added to the fuel. You might want to drain the tank and dump in some fresh gas before you start tackling the rest as it could easily cause rough running depending on the amount of water it has absorbed from the air.
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Wednesday, August 1st, 2018 AT 4:09 PM
Tiny
PATENTED_REPAIR_PRO
  • MECHANIC
  • 1,853 POSTS
What about rust inside the fuel line both blocking fuel flow and causing a too high fuel mixture because of the excess fuel pressure?
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Wednesday, August 1st, 2018 AT 4:35 PM
Tiny
STEVE W.
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  • 13,586 POSTS
I suppose the return line could be plugged or damaged but even then this new pump has an issue because if the return line is blocked the check valve should still retain the higher pressure. Easy way to test that would be to disconnect the steel return line at the fuel nut on the rear of the manifold and run a simple rubber line back into the tank filler. If the pressure drops and it runs better then replace the line. However, I would also expect fuel flow problems from the filter being blocked if it is rust. (Fuel filter is on the frame rail under the drivers door).
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Wednesday, August 1st, 2018 AT 7:19 PM
Tiny
ROBERT CURTISS
  • MEMBER
  • 21 POSTS
I have done 'pinch' tests on the rubber fuel hoses near the fuel filter. I believe I am pinching it enough (with vise-grips) to seal the hose, but still getting a slow bleed of pressure. I have done this with both hoses (pressure and return). I have looked all over for a leak and cannot find one.

I rented the fuel gauge from a local parts store. I will return it tomorrow and rent another from a different store just to be sure of the specs I am getting. 70 psi with power from under the hood, then instant drop to 60, then slow bleed within two minutes to zero.
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Wednesday, August 1st, 2018 AT 7:24 PM
Tiny
STEVE W.
  • MECHANIC
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Instant drop to 60 will be the regulator bleeding off. The slow bleed to zero is the check valve in the pump. It holds the pressure in the system to provide faster starts on a hot engine. The primary symptom seen with a bad one is that you need to turn the key on/off a couple times to make the pump run extra prime cycles.
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Wednesday, August 1st, 2018 AT 8:04 PM
Tiny
ROBERT CURTISS
  • MEMBER
  • 21 POSTS
But the slow start is not the primary issue, it is the rough running and rich engine condition. So the check valve on the pump might be faulty, but not in the way I need to repair.
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Wednesday, August 1st, 2018 AT 8:12 PM
Tiny
PATENTED_REPAIR_PRO
  • MECHANIC
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I was not talking about the return line, but the high pressure line.
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Wednesday, August 1st, 2018 AT 9:20 PM
Tiny
STEVE W.
  • MECHANIC
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Cannot be plugged. You would only get a higher than normal pressure in front of the regulator if something downstream of it was blocked to dead head the pump and stopping fuel flow. If it was plugged before the injectors the pressure at the injectors would be lower, not higher.

Robert -
The bleed down will not be a problem at the moment, just once you get things repaired and it is running correctly.
The higher pressure could cause the rich condition, but with old fuel with a lot of the volatile compounds gone it will not run very good either. That is why I would get good fuel into it. You might be repairing a problem that is being caused partially by the bad gas.
Was it running good when parked?
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Wednesday, August 1st, 2018 AT 10:45 PM
Tiny
ROBERT CURTISS
  • MEMBER
  • 21 POSTS
As far as can be recalled, it was running well when parked. There is not much gas in the tank, basically on 'E'. I do not want to spend the time to drop the tank and am thinking of just getting enough new gas in there to dilute any bad gas in the tank. I know, not the best option, but certainly the simplest. I will get some gas in the tank and recheck the fuel pressure with a new gauge.
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Thursday, August 2nd, 2018 AT 7:30 AM
Tiny
PATENTED_REPAIR_PRO
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When you squeeze the end of a garden hose to produce back pressure the water coming out is under more pressure. That is why it shoots so far out from the water nozzle.
I feel as though I am arguing with another expert on here, how is this helping a customer?
I will stop putting in my two cents worth so at least the customer does not get confused.
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Thursday, August 2nd, 2018 AT 8:50 AM
Tiny
ROBERT CURTISS
  • MEMBER
  • 21 POSTS
Okay, I got hold of a different fuel pressure gauge, no changes. I replaced the fuel filter (and now smell like gas, sigh) while the filter was off, I attached a tube and cycled the fuel pump and removed all the gas from the tank. I poured in a few gallons of newer gas I had on had.

It is still at 70 then 60. The bleed seems much slower, even though there was no fuel leak at the filter (before nor after). It seemed to idle better with the newer gas, but still not right.

After a few minutes, the 'service engine soon' light started to blink. I did not get the truck up to running temperature, but at least enough to get the temperature needle to move.

It is still running at 66 psi Faint white smoke out the tailpipe, ticking noise that I tried to capture on video.

When I replaced the fuel pump, I know I had issues hooking up one of the vent hoses to tank that are not near the fuel pump assembly. I also know that I had issues with getting the busted fittings out of the fuel hoses and had them twisted a bit but they seemed fine on installation. I am hoping not to drop the tank again as it is a pain as a single man job.

Thoughts? I am heading out of town tomorrow until Wednesday so I will not be able to do much more today. I appreciate both of your insights in trying to solve this problem for me.
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Thursday, August 2nd, 2018 AT 11:09 AM
Tiny
STEVE W.
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Blinking CEL is likely a misfire. After setting that long it could be one or more stuck poppets on the injectors, or you could have a valve or two not closing fully.
Being a 1995 this is one of the "fun" vehicles to pull codes on. It was the transition year. GM used a mixed mess on them that is called OBD 1.5 by many. It uses a blend of OBD I coding running on OBD II hardware. The paperclip trick does not work and most of the OBD II code readers won't read them either. There are a couple of the older Actron units that will read them. They are the ones that can read OBD I system but have the OBD II cable.

Some people have been able to get the system to flash the codes by jumping pins 5 and 6 in the DLC but I have never tried it.

Would not worry about the white smoke until you can get it to run and burn off all the moisture in the exhaust system.

We will be here when you get back to it.
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Thursday, August 2nd, 2018 AT 4:33 PM
Tiny
ROBERT CURTISS
  • MEMBER
  • 21 POSTS
Was the ticking noise any help? I am thinking of pulling the trigger on a whole spider unit once I get back. It seems to be such a high fail item from all the forums I have read through. Also, seems like 66 psi is not that much above the specification. I have seen 56-64 psi.

Off to Disneyworld, will not be an issue until I get back!
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Thursday, August 2nd, 2018 AT 10:19 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,586 POSTS
If you are thinking replacement, look at the conversion to the actual multi-port set-up that was used in later years, it is much better than the OEM CPI unit.
I listened to the tick. Could be related to the misfire but it is hard to tell. Once you get back you can use a stethoscope to listen to the engine and figure out what it is. Disable each cylinder one by one and see if it changes. Then work from there. I would not put a ton of money in it until it runs better.

Go enjoy the land of Mouse. We will be here when you come back.
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Thursday, August 2nd, 2018 AT 11:06 PM
Tiny
ROBERT CURTISS
  • MEMBER
  • 21 POSTS
Okay, I have good news and bad news. First, Disney was great, but that is a given.

I ordered and installed a refurbished spider unit. I did not replace the 'nut kit' that includes the two hoses from outside the manifold to the spider unit itself.

Results: Fuel pressure is now about 54 running, maxs at 60 when the pump is primed. The bleed down is super slow, maybe 1-2 psi per minute. Remarkably slower than before.

Bad news: Still have a ticking noise that seems to be coming from the middle of the engine below the level of the manifold. It is still flashing the 'service engine soon' light after about one minute of running, meaning a rich condition, as far as I know.

Where do I go from here? It seems that the fuel issues have been resolved. (Fuel pump, filter and spider assembly). The electrical system seems good with replacement of plugs, cap, rotor. All plug wires seem to be in great shape. Recently replaced before storage.
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Tuesday, August 14th, 2018 AT 11:58 AM
Tiny
STEVE W.
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Flashing CEL means a misfire that is causing a problem. The ticking sounds like a rod bearing but it is hard to say for sure. I would start on one side and pull one plug wire at a time and listen for the sound to change. That will be the problem cylinder. Then do a compression and leak down test. It is possible it is a bad rocker or valve spring.
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Tuesday, August 14th, 2018 AT 5:34 PM
Tiny
ROBERT CURTISS
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  • 21 POSTS
The ticking is the secondary issue. Rich condition (misfire) and rough idle with delayed rpm increases is the main issue. Maybe a bad MAP sensor?
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Tuesday, August 14th, 2018 AT 5:59 PM
Tiny
STEVE W.
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I would try to determine what the ticking is first. Not really worth it to repair the rest and discover you have a bad crankshaft or bad rod bearing or that the engine has a bad valve. The misfire and poor running could easily be caused by a bad intake valve.
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Tuesday, August 14th, 2018 AT 6:18 PM
Tiny
ROBERT CURTISS
  • MEMBER
  • 21 POSTS
The ticking sound definitely comes from higher up on the engine where it is more likely a lifter or rocker versus lower in the engine where would be a rod. That being the case, is there a potential solution to the lifter knock? My goal is to get this vehicle sellable as soon as possible.
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Wednesday, August 15th, 2018 AT 6:03 AM
Tiny
STEVE W.
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That would depend on if it is the rocker, lifter or a broken valve spring. Would not hurt to pull the valve cover and look. If it is on top it is an easy repair. If it is a lifter it should not be hard to replace a bad one as it has roller lifters.
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Wednesday, August 15th, 2018 AT 7:13 AM

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