3800Pro Forums banner
1 - 6 of 6 Posts

·
Registered
Joined
·
5 Posts
Discussion Starter · #1 · (Edited)
93' Pontiac 3800 series 1, just started doing this today.

Starts fine, Idles Fine, but give it some resistance (put in in gear, foot on break), and there is no power, seems like its running on a single cylinder.

If you shift out of gear, it will stall (unless you keep the rpm up). If you keep it from stalling it runs rough for a bit (20-60seconds) then recovers. In a good Idle state, it rev's fine right up to the top without issue.

It doesn't always do this, and it can happen while driving. Loss of power, and will slow to a near stop (jerking motion with each firing). But after a few minutes of blocking the road the "condition" can go away, and I get power again. Can drive for 3 miles or more with out issue and have not found a way to force it.

Turing it off and restarting seems to help, but it take a few attempts. Less likely to do it if its been off for 10 minutes or more.

One Shop suggested plugged Catalytic converter, but I had never heard of that. And another shop doubted that too (no glowing from the converter).

Was suggested that it might be the EGR valve not working.

Installed a New air filter (today, was on the way to get oil change), MAF cleaned in the last 6 months, ICM is 9 months old.

I also ran the engine in 4 cylinder mode for about a month (with two 1000 mile trips on each end) last summer, So I have a good idea of what 6 or 4 or 2 functional cylinders is like. This is two or One, or worse (jerks about 3 times per 2 seconds). Engine sound like its running on two.


Any Ideas?
 

·
Registered
Joined
·
5 Posts
Discussion Starter · #2 ·
I've got codes

21 Throttle Position Sensor Circuit Voltage High
22 Throttle Position Sensor Circuit Voltage High
34 MAF Sensor - Low gm/sec indicated
42 Ignition Control Circuit
56 (known long term issue) QDM "B" Circuit (the EGR and Transaxel)

The EGR is controlled by The TPS, MAF, and Engine temp.

Started and drove the 5 blocks from the parking lot (winter parking ban) to my house this morning, with out issue (engine was cold)

Harness for TP and MAF seem fine (good power and ground). Remotely powering up the TP gives no Signal voltage at any position.

EGR Connector wires are crispy. But the wire do seem to be OK, and power tests good. New connector is $60, so I'm just liquid taping the current one.

No so sure a new TP will fix it, since it drove to where it sits, and the TP is Very dead.
 

·
Registered
Joined
·
5 Posts
Discussion Starter · #3 ·
New TP, tested good out of the car. Clear out the codes, installed new unit. The jerking is gone. MAF is still throwing a code, so I'll gets some cleaner later today.

This is not my first TP sensor to go bad, but the first for this jerk 'symptom'. Its less than an inch off and facing the exhaust's heat shield, so I guess its a no brainier as to why they can cook to death.

I also found addition to the EGR valve connector wire crispy, the transmission connector plastic housing has melted away from the exhaust. So it must have gotten fairly hot in the recent past (likely when I had the trouble last summer)
 

·
Registered
Joined
·
4 Posts
Seems like you got quite a load under the hood there. You could go in for an extensive engine overhaul if the need be, considering the fact that the car is a 1993. Replace all faulty/defective parts and you should do just fine!

On another note, wonder why there no techies replying to you on this one? I am just a noob.
 

·
Registered
Joined
·
5 Posts
Discussion Starter · #5 · (Edited)
I don't agree with an overhaul. As that TP sensor was only 4 years old.

The MAF was dead too. I installed a broken, junkyard pull and now I have no engine codes.

They're all in the same spot, near the exhaust, and two farther-away wiring harness show recent major heat damage. I'm assuming the the electronics in both sensors (yep both have circuit boards in them) just got cooked back when I ran a hot exhaust.

It turns out, running in 4 cylinder mode (disable fuel to a cylinder pair by unplugging the correct injectors, to prevent hydro-lock and cylinder washing) when I had a dead coil pack, The exhaust would get warm, Catalytic converter would glow bright orange, when I pushed the vehicle to free-way speeds (Michigan is 70mph). If a backed off to only 65mph the glow would completely go away. The Engine either run too inefficiently at that load, or one of the disabled injectors leak (but 65mph wouldn't fix a leaking injector)

As to why I haven't got many replies... I think this forum is mostly for Engine Mods not for Stock engines. Mine's Stock except for the electrical power generation.
 

·
Registered
Joined
·
5 Posts
Discussion Starter · #6 · (Edited)
I should also mention that when the used/broken MAF Sensor (broken on sensor end, but still works!) went in I also rigged up a custom harness where I could manually operate the EGR valve.

The 3800 Series 1, has a 'digital' EGR valve, meaning like a 3-bit number, it has three valves, where the second is double the size of the first (p1x2) and the third is double the size of the second (p1x4). This allows the computer to pick any valve size 1to7 times the size of port 1.

Turned out that ports 1 and 3 ran fine, but 2 clicked once and stuck open). Tapping with a hammer would unstick it. I couldn't hear it move back to closed, over the noise of the hammer. But it would then again click and stick. I guessed that it was dirty, and not wanting to break the gasket seal, I kept on hammering then running it until it got stuck.

After about 20 times, it improved (would operate for 3-5 clicks before sticking). I kept at it. It then got to 20ish and would stick (then back to 5). Once I got to 50 working clicks it didn't stick any more (tested through three hundred operations)
 
1 - 6 of 6 Posts
Top