2001 Jimmy 4x4 - Engine Surge While Excelerating

[rolo_az]

2001 GMC Jimmy 4x4; A/C; 140,000.

 

Greetings,

Sorry for the long post, but I think I need to provide a little background as to the repairs that have been done that brought me to this forum.

 

Before all this work I was getting 17mpg & the truck drove great - now 12-13 mpg & can't drive faster than 50mph.

 

In December 2010, my fuel pump went out and had that replaced ($530.00). May 2011 - new alternator ($145). Truck driving great.

 

After hearing stories about leaking intake gaskets, I took it in and had the following done: Intake replaced due to a corrosion hole and 1 injector replaced ($1,500.00).

 

When I picked it up at the end of the day, I noticed the battery light would blink intermittently. Took it back and they "repaired" the wires about 1" from the white connector on the alternator (originally said my new alternator was bad). They also put on a new thermo fan clutch ($130), which seems to never disengage.

 

The manager called and asked about the 4wd light being on. I told him that it comes on after about 5 minutes or 1 mile and that I never use the 4wd (2wd light is always lit). Pickup it up again at the end of the day and the 4wd lights were lit on 4 Auto and 4 Hi at the same time. Caught one guy as he was leaving and he checked to see if the 4wd was engaged (he said not and it was okay for me to drive highway speed & bring it back the next day). It was obvious someone played with the buttons.

 

Brought it back and they "fixed" it. Ever since then this is what was happened.

 

From 0 - 25 - rpm's high and then shifts - no great power. If I back off on pedal, then trans shifts, but it feels like it bogs down.

 

This continues until I hit 40 - 45, then rpm's drop to about 1500 and stays steady to 50 mph. Around 60-65 it felt like it was starving for fuel - surging like you were riding on a bucking bronco.

 

Took it to another mechanic that is closer to home. The code was P0300 and P0410 (no light). Claimed fuel pressure regulator was leaking and recommended the California replacement unit. Looks like fuel reg, injector assy and the six nozzles & new plugs (no wires). (1,300.00).

 

Same low end surging up to 45mph. It runs smooth if I stay around 45-50.

 

I took it in to a tranny guy that I've used for years. His guy put it on the computer & he came back with the following codes. C0305 front prop shaft speed sensor fault; P0101 Mass air flow ckt out of range; P0410 Secondary air inj sys; B2725 Active Tcase mode switch fault; C0265 EBCM relay ckt (ABS code).

 

He said that the dash switch was $72 at GM and I could do it myself. It was definately in 4wd (4Hi), so I went to the nearest chev dealer, bought the switch and installed it in the parking lot. After putting it in N and starting the engine, I pushed the 2Hi button while the 4Hi was blinking, heard a clunk and I was in 2Hi.

 

The tranny guy said MAFS could cause tranny issues so recommending I clean it etc. I cleaned it with MAFS cleaner, but it didn't make a diff. Today I bought a new MAFS ($115) and things really got worse. A lot of jumping/surging from 0-15 and hardly any power. Made it back home and put the old MAFS in (at least it's predictable).

 

I've read on the forum about changing the fuel filter as I've already done the air cleaner etc. It almost feels like fuel starvation but I don't know at this point. I am now broke as I've spent all my savings on this truck. I can't afford to take it in and can't afford a scan tool that I can record while I'm driving etc.

 

Any other suggestions? And a big thank you for making it this far. I am at my wit's end. Thanks again.

[nickvrebel]

Welcome to the forums!

 

I would say one of too things:

 

1. sounds like a clogged catalytic converter. if you try to accelerate too quickly the media in the converter shifts and plugs the exit hole in the conveter and essentially the motor now has no where to push the gases. Take a rubber hammer and gently tap on the converters to see if you hear a rattling. If you do it's bad and have it replaced by a qualified exhaust shop.

 

2. bad fuel pressure. I doubt this, but it is easily checked with a gauge under the hood.

[rolo_az]

Wow, my first reply got zapped.

 

Thanks for responding,

 

I tapped on the cat, pipe and exhaust and to me, it sounded solid (kind of a ting noise - no rattling).

 

I talked to someone about my issues and they say it sounded like a vacuum leak. So today I started to trace out what I could see around the intake. I spotted a vac hose that was plugged into a tee that looked cracked. I cut 1" off and replugged.

 

I found a sensor that was plugged directly into the intake. It felt loose so I unplugged and researched. It was the MAP so I got a new one which plugged in tightly and took it for test. It really didn't change anything. Did find a good reference for this: http://www.obd-codes.com/faq/map-sensor.php Video is great but I wish I had his vacuum pump.

 

Other research talked about the fuel filter and the procedures to release pressure (not sure I want to attempt that yet). I think I saw the fuel pressure release valve (rear of intake next to firewall - no cap). Is this where a fuel pressure test is made or at the fuel filter?

 

 

Years ago, I had a 1990 Chev 1500 that the bottom of the muffler blew out. On my way to get a new cat back set up, going up hill was really bad - no power. The jimmy issue is like that but also with the surging (think of going 20 mph and popping a clutch in 4th gear).

 

Again thanks for your input. I will keep trying and when I get a solution, I will post.

[nickvrebel]

the fuel pressure is relieved at the schrader valve on the fuel line under the hood. a schrader valve looks just like a tire valve stem (well, just the valve piece). There is only one under the hood, the gauge would screw on there.

 

Still sounds like an exhaust obstruction to me, but stuff like this could be a variety of things. I'm just trying to help you check all the things that are easy to do yourself for free. Oh yeah, you can usually "rent/ borrow" for free a fuel pressure gauge from most auto part stores such as AutoZone.

[rolo_az]

I spotted the Schrader valve and the bracket that holds a few what looks like fuel tubes. The bracket seems to be missing the bolt that holds it to the intake. I will need to go to the Chev dealer to see if I can find what size bolt is needed for that. I didn't hear any noise like a vacuum leak, but at least I might be able to eliminate that as the cause once I put the bolt in.

 

Tonight on the way home from work, it threw a P0300 code. The $1300.00 P0300 code fix I spent was suppose to include new plugs, fuel pressure reg and fuel injector 'spider'? and nozzles. The AutoZone printout also mentioned spark plug wires,coil; vacuum leak; injector fault; high or low fuel pressure as possible causes in that order.

 

I'll check with AutoZone about the fuel pressure tester and if that tester will relieve the pressure, I can change the fuel filter.

 

I know that out of the gate, it's a real dog and I have to watch the rpm's, back off the gas at around 2,000, wait for it to drop to about 1,200 before giving it more gas (tranny shifts). I can usually manage this up to 40 mph and then it runs smooth between 40-50 at 1,500 rpm's. I'm really surpised that I haven't seen ticked off drivers behind me .

 

I really appreciate your help on this. It's more now of how much some of this will cost and if I have any money. I'm all for doing the work. It's just I don't have the right tools and money left.

[rolo_az]

I checked the Sec. Air Pump fuses (large 30amp and small 10 amp) both okay. Inspected air pump - cup shaped diaphram looked okay as well as other valves & vacuum lines attached. It appears to have original factory clamps. I will need to get new clamps before removing and testing.

 

I also went to the local GM dealer to see what size bolt was needed for the Schrader bracket. It was a $30 bolt kit, so he removed the bolt and checked the size. It looks to be like an 8mm x 1.25 and about 1.25" long. So I went to Ace, got the bolt and it didn't fit. The location mades it tough. The bolt fell onto the intake. I got my trusty magnetic wand and retrieved it and another new bolt just like it. Seems the mechanic dropped his bolt and he just figured - not my car!

 

At this point, various forums say there are various ways to test the cat - temp front/back, pressure readings etc. I will check the temp when I get to work tomorrow. Too bad these muffler places don't have a way to unbolt the cat back and put in a test unit and then tell me - it fixed the problem you owe me $$$ instead of putting it on, charging me and still have the issue. Very frustating. I've been a GM die hard since '82 and have owned 6 vehicles and this by far is the worst. I sure wish I had my 1990 C1500 again.

[slydog39]

I am no mechanic.

 

My 1999 Burb had issues a while back that had similar symptoms as your vehicle. My problem turned out to be the Throttle Position Sensor. At certain speeds, it would cause serious 'bogging down" issues.

 

It was a $34 part at AZone and was easily replaced--mounted to the throttle body and was easy to get to. I am sure there is a test to determine if your TPS is working correctly without having to buy a new one.

 

 

Good luck

[rolo_az]

I wanted to see if I could look into the cat from the muffler connection, but I couldn't get the nuts off the pipe connector - both were pretty locked in.

 

I replaced the TPS. The old one appeared to have a loose center fitting, but the new one really didn't impove things.

 

Today on the way to work, it shifted fine while below 170 degrees (still couldn't accelerate like it normally could before), but when it got up to temp (about 200) is seriously bogged down to where I couldn't go faster than 20mph. I decided to return home and while on the way, it got up to 45-50. I knew I couldn't get to work (22 miles one way).

 

While in park I can hold 2000+ rpms without any faulter, which makes me think it's more with the tranny (worst case for me).

 

My next step is to take it in to someone who has a lot more experience then me (and a lift etc) and I'll let the forum know what the outcome is.

[rolo_az]

Solution: NickV was spot on. I took it in to a new mechanic and gave him the list was what's been done so far. He said that he wouldn't tell me what it could be but what the problem is.

 

He pulled the O2 sensor in front of the cat and there was a lot of pressure there. He said there was rattling going on, which I couldn't really tell before (sometimes it would be nice to have a lift). He said the cat or cats were plugged.

 

Apparently, there is a pre-cat? that is welded to the pipes coming from the exhaust manifold and I think the other cat was welded on there also. The only bolts were from the cat to the muffler. I'll have to check to see if it's all new or just new cats welding on.

 

So for 700.00 both cats were replaced and I'm running like I was before.

 

The hesitation that I would get starting off and the P0300 codes were due to the distributor being out of adjustment. So the adjustment and cats fixed the issue.

 

I still think I will get the P0410 Secondary Air Pump issue, but I'll have the computer read in about a week.

 

Thanks for everyones help.

[nickvrebel]