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'98 Jimmy loosing rpms and sputtering
Hey, new member and was hoping I could get some advice or direction on repairing my 1998 GMC Jimmy.
Right now, when I start the car it begins at about 800 rpm and over the course of 5 minutes dips to 500 where it sputters and eventually dies. I can accelerate it just fine from any point to higher rpms, but once the accelerator is let loose it returns and sputters. I've been throwing parts at it in a noobish attempt to solve the issue. First was the spark plugs, which had no effect. followed by new plug lines. My friend suggested these as he believed my antenna shaking as it was indicated misfiring. Then the mass air flow filter (this had been an intermittent error in the past). It seemed to breath better, but still no effect. I did get an error during one of those tests for the outgoing o2 sensor, so I replaced that, but still the stalling remained. On a hunch I deleted the cat, my state does not require them and it had a rattle in it for some time. Still the same issues remained. I replaced the fuel filter and tested the pressure after. Pressure was fine, but still no effect on target. Distributor cap and rotor. No dice, though it had some good wear on it. Ignition coil, nothing on that end. I have a controller sitting on the bench, but I feel that won't have an impact. The entire distributor after that, though I had to go back to my old one as the new one gave me a p1345 misalignment. I feel fairly well about my installation, but maybe not about the new distributor's quality. I reinstalled the old one and its working as before. The idle air control valve, and although there is a carbon build up on the old one, still no change. My current direction is better quality distributor, some injector cleaner, then assuming that's no good a new injector which would be costly. This has been quite the learning experience and I know more about how the vehicle operates than ever before. However I also need it running. If anyone has advice or direction to give, I am all ears. |
There are those here who can help you better than I, but I thought I'd give this a bump and offer some thoughts I've picked up that are more general in nature.
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Originally Posted by christine_208
(Post 758841)
There are those here who can help you better than I, but I thought I'd give this a bump and offer some thoughts I've picked up that are more general in nature.
The intermittent mass air flow error was fixed when I replaced the sensor. The O2 outgoing was probably a non starter, and being located after the cat. The error hasn't returned after installing the new sensor and the delete. The p1345 cam misalignment error occurred after the new distributor install, which I found if the mount is not spot on the arc between the cap and rotor are offset. You can fix this by rotating the distributor housing and modifying the mount to hold this rotation. I just put the old one back in and the error hasn't returned. I'm not sure how to find vacuum leaks, though in terms of simple deduction, wouldn't a vacuum leak cause the problem immediately, and not slowly over the course of 5 minutes? |
Originally Posted by Bass_Surfer
(Post 758843)
Now, both you and I know about this distributor-timing thing and t's real.
FTR: I didn't see what engine is in your post --- I'm old and maybe I missed it .... OK ---> that said --
Originally Posted by Bass_Surfer
(Post 758843)
1. You know the post-cat sensor isn't gonna do anything to the performance. Give me a hint on Y/M/M/Engine/Trim/Accessories ... etc.2. Starting, and going to 800 RPM, and slowly dropping SOUNDS like the Idle Air Bypass or the ISC is acting badly - again, depending on the engine in this Jimmy. 3. A vacuum leak will usually cause a high-bump in Cold Start RPM by letting in too much air and since the engines is being told it's cold - the fuel profile is cranked up -- and here's a big clue because 800 RPM is more-or-less "normal" for a temperate climate start-up, relatively cold-soaked engine. 4. Did you in ANY way mess with the crank position sensor or its wiring - even if you didn't remove it, if you unplugged it and then plugged it back in, this can be problematic. Imma leanin' toward a bad coolant temp sensor or a bad ISC. BTW: do you own a scanner that's bidirectional? Starting from the top, the new distributor caused the p1345 error and a lot of missing and worse sputtering than the original problem. Putting the two together and researching online I found others that drilled a hole in their caps, could see the spark crossing at a wide angle, and after rotating the housing to shorten this crossing solved their issue. The new distributor was cheap, and I decided to put my old one back in and if my new idle control valve didn't solve the issue to get something better in quality. A trq is currently on its way. The vehicle is a 1998 gmc jimmy. The engine is a 4.3l v6. 1: The outgoing o2 sensor lead me to believe it was an air flow issue, and because the cat was rattling at the time, a delete seemed like as good a direction to go. I'm not after performance, lets start with functionality. 2: The engine is a 4.3l V6. I've attempted to replace the IAC installed on the drivers side of the intake manifold, but again no effect there. 3: I've had a fuel pressure gauge during one of these tests but didn't see any change from start up until it died. There is an access port near the distributor that I used for that. 4: I've not touched the crank position sensor or wiring. Considering I've narrowed the new distributor's crappy timing as the culprit for the new issues, I don't think this avenue is correct. Tell me about this coolant temp sensor and how it may cause this? After 5 minutes it stalls out, and while I can get it to start right after it remains at a low rpm until its sat for a while to cool down? I don't own a bidirectional. What I am using can read and clear codes and that's about it. |
Originally Posted by RyanJB
(Post 758844)
Starting from the top, the new distributor caused the p1345 error and a lot of missing and worse sputtering than the original problem. Putting the two together and researching online I found others that drilled a hole in their caps, could see the spark crossing at a wide angle, and after rotating the housing to shorten this crossing solved their issue. The new distributor was cheap, and I decided to put my old one back in and if my new idle control valve didn't solve the issue to get something better in quality. A trq is currently on its way.
From the factory, the distributor is locked in place by the hold-down to prevent those who think they can set a base timing from changing it. However, due to distributor gear wear and timing chain wear/stretch, cam sensor retard can get outside of 0 +/- 2 degrees and this sounds like what you may have. If fault is in the distributor gear, you should feel slop back and forth when manipulating the rotor. If so, pull the distributor and look for wear on the gear. Cure is new distributor gear or new distributor. But probably not worth a timing chain replacement to correct cam sensor retard. Replace the hold down with a standard SBC hold down so the distributor can be rotated. With the engine running, monitor cam sensor retard and turn the distributor until it is zero. Raise RPMS above 2500 and allow to idle again - should come back to zero +/- 2 degrees. If you get the distributor in a tooth off, the rotor will be 360/13=27.7 degrees off Other than not connecting the cam sensor electrically, this is pretty much the only thing that will set a P1345. A P1345 sets when cam sensor retard is excessive - so it is saying that you have exceeded the working range for rotor to terminal distance and are entering the range of another cylinder. Makes things misfire. Turning distributor doesn't change ignition timing one iota, as that is determined by the PCM. Cam Sensor Retard is also called CMP Retard in some scanners. Not that many inexpensive ones will check it on 1996-2004 Blazers or 1998-2001 V8 pickups. Car Diagnostic Pro (as is) and Torque Pro (with a custom PID) are two inexpensive bluetooth OBD2 scanners that will do the job. Good luck |
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Originally Posted by LesMyer
(Post 758845)
I can see that you realize that turning the distributor does not affect the ignition timing. What turning the distributor does is to align the rotor with the cap terminal enough that when the spark comes across it doesn't misfire. Since there is a cam sensor inside of your distributor, this can be accomplished by setting you cam sensor retard value to 0 +/- 2 degrees. This give optimum alignment for rotor to terminal when the spark happens. There is no base timing to set, and you cannot change the timing the PCM decides to use.
From the factory, the distributor is locked in place by the hold-down to prevent those who think they can set a base timing from changing it. However, due to distributor gear wear and timing chain wear/stretch, cam sensor retard can get outside of 0 +/- 2 degrees and this sounds like what you may have. If fault is in the distributor gear, you should feel slop back and forth when manipulating the rotor. If so, pull the distributor and look for wear on the gear. Cure is new distributor gear or new distributor. But probably not worth a timing chain replacement to correct cam sensor retard. Replace the hold down with a standard SBC hold down so the distributor can be rotated. With the engine running, monitor cam sensor retard and turn the distributor until it is zero. Raise RPMS above 2500 and allow to idle again - should come back to zero +/- 2 degrees. If you get the distributor in a tooth off, the rotor will be 360/8=45 degrees off Other than not connecting the cam sensor electrically, this is the only thing that will set a P1345. A P1345 sets when cam sensor retard is more than 22.5 (45/2) degrees plus or minus - so it is saying that you have exceeding the working range for rotor to terminal distance and have entering the range of another cylinder. Makes things misfire. Turning distributor doesn't change ignition timing one iota, as that is determined by the PCM. Cam Sensor Retard is also called CMP Retard in some scanners. Not that many inexpensive ones will check it on 1996-2004 Blazers or 1998-2001 V8 pickups. Car Diagnostic Pro (as is) and Torque Pro (with a custom PID) are two inexpensive bluetooth OBD2 scanness that will do the job. Good luck I did notice some play in the rotor when replacing the old cap and rotor. To rephrase your instructions: after installing the new distributor and a SBC hold down, I should use a bluetooth obd2 with car diagnostic pro, monitor the cam sensor and rotate the distributor housing while idling until the reading is zero. Once done, rev to 2500rpm and return to idle and assess the offset. Assuming I got that right, would you recommend an inexpensive bluetooth obd2 reader to go along with the app? I'd like to also note that there is a metal tab in the center bottom of the distributor shaft. I've attached picture of it (not mine). I was lead to believe that it prevents the distributor from seating properly unless the teeth are in the proper order (or 180deg apart). I didn't force the new distributor in and was careful with the orientation when putting it in. Which is why I assumed it was a premium chineesium part. Am I wrong about its purpose and actually get it 45deg off? |
Originally Posted by RyanJB
(Post 758846)
To rephrase your instructions: after installing the new distributor and a SBC hold down, I should use a bluetooth obd2 with car diagnostic pro, monitor the cam sensor and rotate the distributor housing while idling until the reading is zero. Once done, rev to 2500rpm and return to idle and assess the offset.
Assuming I got that right, would you recommend an inexpensive bluetooth obd2 reader to go along with the app? Mine is a BAFX OBD2 adapter from 2014 but they stopped making them a while back. Was about $20 and I was impressed that it would do 30 PID scans/sec in Torque Pro on my 2001 Blazer (while other one I bought would only do 6 scans/sec). Torque Pro only because it would measure it. Car Diagnostic Pro gives you more bang for your buck as it can read/clear all the codes including HVAC, body, SIR, Antilock, etc and has limited bidirectional functionality (very limited). . SEE POST #21 - THINK I FOUND A BETTER ONE. |
Originally Posted by Bass_Surfer
(Post 758848)
I can see there's someone in the audience who doesn't believe you can affect the ignition timing by moving the distributor --- now I gotta find out where he lives so we can pick a convenient parking lot to discuss this ..... <ahem!>
The facts of the matter can be distilled down to be that spark timing is initiated based upon CKP readings as referenced by the ECM which then pulses the coil through the ICM based upon operating criteria from its spark lookup table (now there are other factors that influence this lookup table, but I am simplifying things for the sake of discussion to not bog it down too much). The coil then sends spark through the distributor. So no, you cannot affect base timing by rotating the distributor. To do that, you would have to change the CKP to crank relationship or ECM tuning. This goes back to the last time that Les corrected you as well (and the only other time you were confronted with your lack of working knowledge on these ignition systems) when he stated that there is no pickup in the distributor as this holds true for any crank trigger ignition system. The trigger location matters. The only thing you are doing by rotating the distributor is changing the alignment of the rotor to the cap to better allow for the spark to jump in the entirety of the advance curve which is why it is important to get the CMP Retard value in specification per the procedure that Les has laid out. That is all. Thank you for your attention to this matter. :icon_deadhorse: As far as your anecdotal evidence, you provided no other information so I could assume that there were other factors at play and that your CMP Retard was out of spec and you simply brought it back into spec with your adjustment. Not really anything to discuss here in this thread without pulling it even more off topic though so feel free to create a thread of your own if you want to continue this discussion. |
Almost forgot, the square tab in the center of the distributor gear meshes with the oil pump drive shaft. As you apparently discovered, if it is not engaged with the oil pump shaft it sits on top of it and prevents the distributor from dropping down all of the way. Sometimes you need to turn the driveshaft to a proper position so it engages when the distributor goes back in. You can see it if you shine a light down the distributor hole. I have a huge foot-long screwdriver that I use to turn it. It's kind of a trial and error thing. Turn it just a little and try the distributor. Move it a little more and repeat. Repeat until distributor drops in all the way.
If you don't have a SES light with P1345 code setting, you can mark rotor position on the firewall with a sharpie before you take the distributor out - and put the distributor back in with the rotor pointing directly at that mark. That's the easiest thing to do. If you have complications of some sort for whatever reason, then you go to the put engine on TDC #1 and drop distributor in with the rotor pointing to the "6" cast into the cap mating surface method. Most likely you won't need to do it. The reason I am first pointing you to set your cam sensor retard (to possibly cure your problem) is because it is such a common performance problem on this particular system - and it seems you are already onto it. If it isn't the problem, we can do other testing of live data before replacing parts. That's where the scan tool comes in. Lots of stuff you can do with a scan tool, fuel pressure gauge, and compression tester without shooting the parts cannon! So please get that cam sensor retard set. If your gear is OK, you can take off the factory hold down, use your old distributor with a SBC hold down, and save some $$$. Would only cost you some work to try it. You may want to stop by the hardware store and buy a longer hold down bolt and a flat washer. Blazer hold down bolts are metric and smaller diameter. Take the old one with you for sizing. Best wishes |
THIS THREAD has the book method for timing these EDI ignition systems. I figured I would throw it in here as I found it in my musings a bit ago.
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