I have a 98 GC 3.0l with 123k miles on it and it has just about no power. I just recently replaced all the idler pulleys and timing belt (and all the seals on that side of the engine). I have tried a new MAP sensor and it had no effect - I previously had a P0108 and got a junkyard MAP sensor that fixed that, but I wasn't sure about it when this problem started.

Anyways to describe the problem, if you give the van a little gas (no more than 35% throttle) then it will go, but it has no guts behind it. Your only other option is to floor it, and then it goes, but not like it should. For example, if you turn on the AC, there is so little power left over you can't accelerate past about 10MPH, unless you floor it. Also you get some backfiring/popping at around 3k rpm if you've stomped on it. And lastly, it does this sort of thing even in neutral or park - like it just won't rev up worth a damn, and just sits and grumbles if you have the AC on.

I have a scangauge (hence knowing the throttle position) and the MAP readings seem a bit off - at idle it often reads 7.4-8.9 (PSI) and if you give it a bit of throttle it will give numbers that seem more normal given the throttle position and engine RPM. This was what led me to try a new MAP sensor in the first place.

Any suggestions as to what to look for? I have code P0403 (And today I got P0400?) on the ECU, but I have not made the time to clean the EGR stuff yet. Could it be simply the EGR? Someone suggested I check the catalyst to be sure it wasn't plugged or melted down, and I did that today (it's fine), even going so far as to rev the engine with the exhaust off and it was the same as with it on.

Also, the van's (recent) previous owner replaced the plugs wires and distributor in the last 3 months or so.

 

How did the engine run before you did any repair work?

 

I'd say (with my limited caravan experience) that it ran fine - also, it ran fine after the repair work for at least a month before this started a few days ago. It even ran fine with the 'bad' MAP sensor (P0108 error). I will add that I did test the fuel injectors while I had the intake off and they were all well within spec with a good pattern. (we have a tester where I work)

Today the ECU reset it's codes and on the drive home threw up different codes - p0108, P0401, P0000 and P1297. It's behaving a bit oddly, though - when I hit scan codes, at first it brings up the P0108, but when I scroll to read the next and then go back the P0108 is missing from the list. I'm wondering if I have an ECU going bad? I have been considering running new wires from the ECU to the MAP sensor to see if that fixes my problem.

The P0108 is probably happening because I put the wrong (bad) MAP sensor in instead of the good one, I got them mixed up when I was trying with the new sensor. The P1297 is listed by alldata as "No change in MAP sensor from start to run", apparently meaning it didn't change readings from key on to after starting the engine.

 

ck reg. & vac. line

 

Okay, an update: things are a little better now (inexplicably) when the engine is hot but still so little power that turning on the AC kills any chance at acceleration.

I was able to do some more checking on it today, the engine timing is still correct (no slipped cog), pulled apart the intake and checked things over, the EGR moves freely, only vacuum leak I could find was the stupid cruise control hose was snapped but that is a tiny leak, and fixed now. I checked the distributor cap and things look good under there as well.

I did verify that the backfiring/popping is coming from the intake.

I have not yet had a chance to check the fuel pressure but will try to do that tomorrow on my lunch break.

 

If you are getting a backfire, then you are either having a misfire problem a timing problem.

 

Thanks master tech, I will put a timing light on it tonight as well, perhaps the timing is just off?

Also got a P0180 code this morning when I went to reset the codes and checked through them... Apparently this code is for fuel temp? Except I didn't think these vehicles had a fuel temp sensor? Maybe my ECU is going bad.

edit: went for lunch and the damn thing came up with another new one... P0080 (exhaust valve control solenoid circuit high)... wtf? Keep in mind I don't have ALL of these codes at once, for instance right now I have P0080 P0401 P1297 and P0108

 

Sounds like a bent push rod or valve ? or rocker arm with hole worn thru ? or maybe cam lobe worn off ? Bud

 

Got a little more info for you guys today, I did attempt to check the engine timing and the light agreed with what the scangauge reports, but I have no idea what it is supposed to be from the factory?

I checked the TPS sensor voltages; at idle (fully closed throttle body) it is .97v and wide open is 3.97v. My Alldata says the closed voltage can be anywhere from .38 to 1.2v but .97 seems pretty high to me. The computer reports the TPS at 20 when it is closed and 78 wide open.. Think this could be my problem?

I will be making a fitting to stick on the fuel line so I can check the fuel pressure tomorrow with the engine running.

lovvorn: I sure hope it's not a bent valve or anything, I suppose I could run a compression test to check this, and if it fails then run a leakdown test at work. It's SOHC so no pushrods.

 

Try doing a compression test too, This way you can see what the plugs look like too. You could also have a bad cap or rotor too.