1998 RT C200V fuel pump replacement?

[KaptainK]

I believe I've got a bad fuel pump. The truck will always start and sometimes run beautifully, and other times it acts like it's running out of gas when I hit the throttle. Big bog, cutting out, throwing 02 codes on bank 2, sensor 1.
Fuel pressure test shows 60psi with key on, engine off, and about 52 during idle.
When I blip the accelerator, the pressure should instantly go to 60psi, but seems to modulate all over the place around 58-62, very erratically. I thought it might be a ground or wire issue, but I am getting 7 amps across the relay, and I think that should mean it's fine, wiring wise.

I'm 'almost' convinced i need a fuel pump, but am still diagnosing. Does anyone know if the tank and pump replacement are the same as a stock chevy express?

Edit: Just did fuel pressure test again. 60psi key on, engine off. 55 psi at idle. Spikes to 62psi when I stab throttle, then drops back down to 55 at higher rpm (less vacuum). That actually may be okay? Oye, back to the drawing board.

TiA! Kaptaink

[SteveJ]

I can't help on the pressure specs, sorry.

The fuel pump in the RT has an extra tap for the feed line to the genny.

One other possible solution may be to clean the catalytic converter. I was having bogging issues, especially after starting the engine warm. I gave it a large dose of Cataclean and it ran much better and the warm start problem went away. IIRC, the van had about 160k miles on it at the time.

[booster]

Originally Posted by KaptainK

I believe I've got a bad fuel pump. The truck will always start and sometimes run beautifully, and other times it acts like it's running out of gas when I hit the throttle. Big bog, cutting out, throwing 02 codes on bank 2, sensor 1.
Fuel pressure test shows 60psi with key on, engine off, and about 52 during idle.
When I blip the accelerator, the pressure should instantly go to 60psi, but seems to modulate all over the place around 58-62, very erratically. I thought it might be a ground or wire issue, but I am getting 7 amps across the relay, and I think that should mean it's fine, wiring wise.

I'm 'almost' convinced i need a fuel pump, but am still diagnosing. Does anyone know if the tank and pump replacement are the same as a stock chevy express?

Edit: Just did fuel pressure test again. 60psi key on, engine off. 55 psi at idle. Spikes to 62psi when I stab throttle, then drops back down to 55 at higher rpm (less vacuum). That actually may be okay? Oye, back to the drawing board.

TiA! Kaptaink

Long shot, but maybe could be related if the fuel system is a return type instead of the more common type these days dead end system.


The return systems use a bypass regulator back the tank and can show oscillations like you are seeing when the regulator gets sticky. Of course it can also be the regulator in the fuel pump itself if it has one on any system.

[hbn7hj]

Originally Posted by SteveJ

The fuel pump in the RT has an extra tap for the feed line to the genny.

Mine does not so I suppose the answer is some do, some don’t. You should remove the old one to be sure you get the correct replacement.

2003 Chevy 190 P

[mkguitar]

on my 2001 GMC4.8 I had hesitation/ pinging on acceleration & low O2 codes
my psi was closer to 45 than the spec'd 60 ish

( find your specs- mine may differ)
the combination of trouble codes and then testing the pressure on the fuel rail confirmed



on a pickup it's easy, 8 bolts and a couple of taillight connectors to tailights and slide the bed back- i had to change the wiring connector with supplied pig tail
$220 autozone- the entire job took 4 hours by myself incl picking up the pump



in the van you'll have to drain & drop the tank- adds to the complexity


my genny feed is a tap in the side of the tank at about 1/3 level


yours may differ


Mike

[Roadtreker357]

Originally Posted by SteveJ

I gave it a large dose of Cataclean and it ran much better and the warm start problem went away. IIRC, the van had about 160k miles on it at the time.

Thanks for the Cataclean tip, Steve. Recommended dosage is 450 ml of Cataclean in 4 gallons of fuel. Did you use a good bit more than this ratio? Sounds similar to triple dosing Seafoam to clean a carb and get a generator running.

Makes me think, wonder if the onboard generator ought to be run to clean it too.

[SteveJ]

Originally Posted by Roadtreker357

Thanks for the Cataclean tip, Steve. Recommended dosage is 450 ml of Cataclean in 4 gallons of fuel. Did you use a good bit more than this ratio? Sounds similar to triple dosing Seafoam to clean a carb and get a generator running.

Makes me think, wonder if the onboard generator ought to be run to clean it too.

as there is no way to reasonably get the tank to 4 gallons without being in danger of running out, I treated the last eight gallons, +or-. Once dosed I gave the RT a good "Italian tune up" for about 20-30 miles. It was still running well last week when I sold it.

[mloganusda]

Have you looked at the fuel filter? Could be partially plugged.

MLogan
Smyrna, TN

[TX-Trek]

Originally Posted by KaptainK

I believe I've got a bad fuel pump. The truck will always start and sometimes run beautifully, and other times it acts like it's running out of gas when I hit the throttle. Big bog, cutting out, throwing 02 codes on bank 2, sensor 1.
Fuel pressure test shows 60psi with key on, engine off, and about 52 during idle.
When I blip the accelerator, the pressure should instantly go to 60psi, but seems to modulate all over the place around 58-62, very erratically. I thought it might be a ground or wire issue, but I am getting 7 amps across the relay, and I think that should mean it's fine, wiring wise.

I'm 'almost' convinced i need a fuel pump, but am still diagnosing. Does anyone know if the tank and pump replacement are the same as a stock chevy express?

Edit: Just did fuel pressure test again. 60psi key on, engine off. 55 psi at idle. Spikes to 62psi when I stab throttle, then drops back down to 55 at higher rpm (less vacuum). That actually may be okay? Oye, back to the drawing board.

TiA! Kaptaink

You mentioned O2 codes but you didn't mention what those codes were.

I think your fuel pressure is ok, some mild fluctuation at throttle demand is expected as the ECU will command more fuel, then decrease as the throttle is closed.

I would suggest having a good scantool that can read live data and the individual vehicle modules. On a 98, there are fewer modules, but on newer, there are many. But anyway, looking at live data, is the engine going into closed loop on both banks?

The O2 fault is giving you a direction to diagnose.
When the engine is cold, the ECU goes into a pre-programmed open loop until the O2 sensors become operational/reach temperature, or the engine coolant temp reaches a certain point. I'm not sure if you have heated or non-heated sensors on your model year. Typically non-heated sensors are 3 wire, heated sensors are 4 wire. The ECU then goes into closed loop which now uses O2 sensor data for fuel control rather than the pre-programmed open loop fuel control. I'm guessing these are narrow band sensors that provide exhaust rich/lean voltage data back to the ECU. Along with throttle position, MAP/MAF, the ECU will then control the injector pulse width for more or less fuel. The upstream (pre-cat) O2 sensors will constantly switch voltage - voltage should cycle or fluctuate within the 100 mV-900 mV (0.10 to 0.90V) range. If the voltage is lazy or not fluctuating then there is an issue with the O2 sensor.

When the O2 sees a rich mix, voltage will fluctuate up towards the .9v, as it sees a lean mix voltage will fluctuate down towards the .1v. You should see this voltage oscillate back and forth constantly.

The downstream (post-cat) O2 sensors are there to verify catalyst efficiency - they will typically remain at a constant voltage or percentage. It's generally more common to have the upstream sensors fail, but again, a scantool should show their operation when the engine is running. In your case, it may be a failing O2 sensor resulting in the ECU losing fuel control and the engine bogging. But this needs to be verified.

O2 sensors can be like shocks - they can get lazy over time and you may not notice a day to day difference until they get pretty bad.

Also, that scantool should catch a freeze frame when any CEL is commanded on by the ECU. The freeze frame records all run data when the CEL is on and can be a help to diagnose an issue, looking for a reading out of norm.

On some vehicles such as our 2010 RT (Chevy Express) the fuel filter is part of the fuel pump assembly and not a separate in-line filter.

[KaptainK]

I replaced the cap and ignition control module. Didn’t help.
Purchased a Veepeak OBD module and am running some live data with OBD Fusion.
I also have a 2000 GMC with the same 5.7 engine to compare values.
I did go into Closed loop and had good activity on the O2 sensors. My intake air temp was reading 228, which was quite different from the other 5.7. It read 52’ , very close to ambient air temp. I unhooked the intake air temp sensor and got no code. I took it for a drive, and it ran perfectly for over an hour. OBD fusion showed the intake air temp slowly drop from 228 down to 182. I don’t know why it was giving a reading with the sensor unplugged? At any rate, I was trying to burn up some fuel, since I have injector cleaner and fuel treatment in there. Still could be bad fuel, or water in the fuel I suppose.Occasionally, when it bogs down, a few sharp stabs on the accelerator will get it firing again. Still comparing live data to look for discrepancies between the two engines. I replaced the fuel filter already.
Also, I do have a exhaust manifold leak, which may be the cause of the high intake temp. Can’t figure out why sometimes it runs great, while other times it just loses power and seems like it’s out of gas or spark.

[TX-Trek]

Originally Posted by KaptainK

I replaced the cap and ignition control module. Didn’t help.
Purchased a Veepeak OBD module and am running some live data with OBD Fusion.
I also have a 2000 GMC with the same 5.7 engine to compare values.
I did go into Closed loop and had good activity on the O2 sensors. My intake air temp was reading 228, which was quite different from the other 5.7. It read 52’ , very close to ambient air temp. I unhooked the intake air temp sensor and got no code. I took it for a drive, and it ran perfectly for over an hour. OBD fusion showed the intake air temp slowly drop from 228 down to 182. I don’t know why it was giving a reading with the sensor unplugged? At any rate, I was trying to burn up some fuel, since I have injector cleaner and fuel treatment in there. Still could be bad fuel, or water in the fuel I suppose.Occasionally, when it bogs down, a few sharp stabs on the accelerator will get it firing again. Still comparing live data to look for discrepancies between the two engines. I replaced the fuel filter already.
Also, I do have a exhaust manifold leak, which may be the cause of the high intake temp. Can’t figure out why sometimes it runs great, while other times it just loses power and seems like it’s out of gas or spark.

I'm not sure why you replaced the cap/module - a primary or secondary ignition problem is more typically evident as a steady event either at idle, off-idle or under load.
Does your scantool retain stored or past codes? As mentioned, the code(s) can help point to a direction, especially to see if the O2 code was related to sensor or circuit.

An exhaust leak doesn't affect inlet air temps. But it does affect O2 readings and can eventually damage the catalytic converter if an overly lean condition continues - the converter can overheat.
Speaking of the IAT, yes, that sounds like an issue with the sensor or circuit, especially if you have the stock airbox which draws true outside air. Many "cold-air" intakes actually draw highly heated air from inside the engine compartment. Removal of the IAT may have caused the ECU to go into a default mode on the air temp, but only dropping to 182d for outside air still seems out of whack.

I believe your trouble is related to fuel delivery, not ignition. But fuel delivery counts on a variety of inputs, such as the O2's, throttle position, manifold vacuum, etc., not just fuel pump/regulator. Again, I would look to see what that O2 code was about. Also, related to the O2's - the rear O2 readings could help clarify condition of the converter.

And you're right about poor or contaminated fuel causing this issue, including fuel with excessive alcohol or water content. Our son's 07 Suburban started running terribly, all sorts of codes, slamming gears, ABS lights, you name it. He thought it might be the ECU failing. We checked powers and grounds but all was ok. Then his wife mentioned it was after she filled it up. I used my scantool to read that the alcohol content of the fuel was 70% - WAY over, even for his flexfuel vehicle. Station paid to drain the tank and refill - problems immediately went away.

[SteveJ]

I ran the OBD Fusion in my 2000 200 with the 5.7 engine. Once moving down the highway the intake air temp was about 5* over ambient. It would climb in stop and go traffic, especially in the heat with the AC cranking.


HTH.

[KaptainK]

There does seem to be an issue with the bank 2/1 sensor. My first scan showed voltage staying between.5-.8V, with corresponding -30 stft. Last night, I got the opposite result. O2 voltage seemed to be stuck between .1 and .4 V, with a +30 stft. And just this morning, it threw a code for 02 sensor 2/1, P0154; “no activity”. Bad wires or 02 sensor. Bank 1 looks fine, I can see the voltage going up and down, as expected, with small numbers on the fuel trim. Could a bad O2 sensor wreak this kind of havoc?
Still no clue why IAT reads over 200’. Plugged or unplugged, the reading isn’t anywhere close to ambient temp. Shouldn’t unplugging the sensor give me a maxed out reading of 0 or 300?
Could I be getting some kind of voltage induced on the IAT wires, causing the ecu to see it as high air temp?

[booster]

Originally Posted by KaptainK

There does seem to be an issue with the bank 2/1 sensor. My first scan showed voltage staying between.5-.8V, with corresponding -30 stft. Last night, I got the opposite result. O2 voltage seemed to be stuck between .1 and .4 V, with a +30 stft. And just this morning, it threw a code for 02 sensor 2/1, P0154; “no activity”. Bad wires or 02 sensor. Bank 1 looks fine, I can see the voltage going up and down, as expected, with small numbers on the fuel trim. Could a bad O2 sensor wreak this kind of havoc?
Still no clue why IAT reads over 200’. Plugged or unplugged, the reading isn’t anywhere close to ambient temp. Shouldn’t unplugging the sensor give me a maxed out reading of 0 or 300?

It is hard to tell exactly what will happen on any given vehicle unless you can see how they are actually programmed. My guess would be an O2 sensor that shows inactive would put the pcm into a non corrected mode basically eliminating all the long and short time fuel trim, but not certain on that. If it is going on and off it could drive things a bit manic I think. If it thinks the IAT is 200* it will have the mixture running lean in most cases. If the IAT is showing a fixed amount I would think you would get a code, though.



Your 2000 engine is probably a generation one 5.7L so it would not have the more current LS engine programming. It is also likely to be similar to the gen 2 LT1 engine I have in my 1996 Buick Roadmaster. I have that programming read out and I will try to get a look and see if I can tell how they handle those two functions. It is a rather complex program and there aren't really any instructions how to use them, so it will take a while to find much, I think. IIRC they do have max and min correction factors for a lot of things and a list of what codes are set and how. Should know more by tomorrow.


There is, however, no doubt those two items need to be fixed, so probably should count on it.


Dose your scanner have a way to data log a drive and record it?

[TX-Trek]

Written responses can sound snarky, that's not intended here, but that's what I've been trying to tell you about looking at the O2 sensor code and it's relationship to fuel trim levels.

If it's a 3 wire sensor, that circuit has a ground, reference voltage from the ECU and sensor voltage back to the ECU. As the O2 sensor reads the exhaust gas mixture it changes the supplied reference voltage back to the ECU - that's what the ECU uses to supply or remove fuel. A 4 wire includes O2 heater circuit.

My assumption from your readings is that the wiring may be ok but the sensor itself may be failing and/or the sensor connector may be damaged or corroded, adding to the inconsistent readings.

As you can see sometimes the trim goes full negative meaning the ECU is reducing lots of fuel, other times trim goes full positive meaning the ECU is adding lots of fuel. The 2 banks are not isolated so if one bank is messed up it will affect the other bank as well.

So yes a bad O2 can cause the havoc, as mentioned the ECU doesn't know what to do for fuel so it defaults to a set strategy.
A safe and inexpensive path is to replace that O2 sensor with oem brand, cheap after markets don't always have the same calibration as oem sensors.

I would also suggest that if your vehicle us equipped with Mass Airflow Sensor (MAF) it be spray cleaned with specific MAF cleaner spray. Not carb cleaner and don't touch the wire just spray clean it. The ECU uses MAF data to verify throttle position and air flow into the engine along with O2 etc inputs to calibrate fuel supply, ignition timing, transmission control etc.

On the IAT I can't tell you what's going on with that without looking at circuits and specific vehicle specs.

[booster]

I took a quick look at the 96 program and the IAT doesn't seem to trim fuel, at least that I found, but it will take out a bit of timing at that temp. It also showed IAT hi or lo should set a code, so you have to be within the range. The fact that it doesn't change unplugged is a bad sign and would indicate something bad. Depending on the sensor type and wiring it could be a wire leaking, but it also could be the PCM is bad. Sometimes people have added resistors to the IAT and/CTS to fudge mixture, but it is pretty rare so not likely.


If your scanner lets you see open or closed loop, take a look at that when the O2 sensor is going wonky back and forth. The program showed it will set code for hi or low voltage, and also intermittent, so it is checking all of them most likely. The normal PCM reaction to major O2 issues is to take the the engine to open loop and open loop with a 200* input could be pretty weird.



Do you have two or four O2 sensors? At a minimum I would replace the two front ones together as they usually fail close together anyway. Replace both if you only have two.


Also remember that an injector intermittent or ignition intermittent can also drive an O2 sensor nuts and bouncing around. It usually will set some kind of a miss fault those.

[KaptainK]

I’m not trying to be snarky either, lol. I am trying to check the O2 sensor! That’s why I bought the scan tool and I’m posting voltage results along with fuel trim. Trying to get a basic understanding of how to interpret the data.I ordered a new O2 sensor this morning. For 50 bucks, I’ll give it a try.

[TX-Trek]

Originally Posted by KaptainK

I’m not trying to be snarky either, lol. I am trying to check the O2 sensor! That’s why I bought the scan tool and I’m posting voltage results along with fuel trim. Trying to get a basic understanding of how to interpret the data.I ordered a new O2 sensor this morning. For 50 bucks, I’ll give it a try.

Understood, no problem - happy to try to help and give overview of sensor operation.
I think Booster is on same path on the diagnostics too.

You typically want to see upstream O2 sensors transitioning voltage fast and often. That means they are reacting and reporting exhaust gas oxygen levels. Downstream sensors should remain at almost constant voltage to indicate high cat efficiency.

Open and closed loop refers to fuel control. Open loop is cold start running fuel trim on pre-programmed data.
The ECU doesn't use O2 sensor input until the fuel system reaches closed loop, what we typically think of as engine coolant reaching a certain temp. That's part of it but mainly dependent on O2 sensor element reaching temp.

STFT is that instant fuel trim data you see fluctuating related to O2 sensor input (voltage). Ideal 14.7:1 ratio is 0 STFT or O2 narrow band sensor voltage at .450. STFT ideal range is +/- 5% from 0. That's why good O2 sensor operation is so important to the fuel strategy - a lazy or defective O2 sensor creates problems.

LTFT is the longer term fuel strategy the ECU develops based on STFT data. It's essentially the trend of fuel added or removed over a number of drive cycles.

I think your sensor replacement was prudent - bear in mind that after it's installed and reporting correctly you may or may not see any further issues with fuel trim. Sometimes there's another issue with a vacuum leak, leaky injector etc but can't be seen until O2s are reporting correctly. Not saying this is the case here, just something to keep in mind.

[KaptainK]

Thank you, I appreciate the help. As luck would have it, despite my careful approach, I rounded off the corners on the sensor while trying to replace it. I had already cut the wires so it’s dead now. This makes me wonder why I have cutting out issues in open or closed loop? As I guessed, it runs just fine with that sensor unplugged. I’m about 50/50 success... It seems to run great and stay solid, or it immediately Boggs down after leaving the house. It doesn’t seem to run great for a while and then start to poop out. When it doesn’t want to work right, it shows up immediately. Weird.

[booster]

The chugging is an interesting description as I normally hear missing, hesitating, etc type stuff. In my mind chugging would be like a vehicle being in too high a gear so it feels like it is not able to accelerate run smoothly.


The fact that it is also acting like an on/off switch may indicate that is what is triggering it. If it didn't change with the O2 cut out, it would also be on both banks which the description would also indicate.


There are only a couple of things I can think of in the controls that would do such a thing. One would be that the pcm is putting it in to power reduction mode because of a fault like an overheat situation either in the engine or transmission. It could be a false fault because of an intermittent sensor. Another would be that it is thinking it needs less power than it really does and is intentionally reducing the fueling. This could also be sensor related if the MAF, MAP, or other sensors indicated it should do it. If the torque converter locks up early, at too low a speed for the gear, you also get that same loss of power feel and they do lock it when the trans hit high temp limit in many of the GMs if not all.



Of course there is also a chance the pcm is going bad, which certainly does happen in 20 year old vehicles.


Two things that might cause a more minor power loss would be the EGR system and crankcase and tank vapor purge cycles if they happen at the wrong times.