Trouble setting timing on 1996 GM 2.2l engine

Hi All,

I have a 1996 GMC Sonoma extended cab, 2.2l engine (not vortec) purchased in the United States. I’m having trouble setting the timing correctly.

I recently replaced the camshaft and crankshaft sprockets and chain, and after several attempts to set the timing, the engine still shakes badly and struggles to run smoothly, especially at idle. (It did not do this before the repair.) My code reader picks up the following codes: P0106, P0108. It seems to me that the timing is off despite my best efforts.

I’m going to try and attach a picture of the timing chain and sprockets as they’re currently set, because the camshaft timing mark is strange on this vehicle and I’m not sure if it’s lined up correctly. Can anyone tell me if it looks right? (Red mark on cam sprocket made by me; timing mark is supposedly the circular hole above that tooth.)

I did several other repairs at the same time that I did the timing. I have gone back over as much of these as possible and I don’t think I did anything wrong. As cars go I’m stricly an amateur but I work as a small engine mechanic so I have some experience with the way things feel when they’re done wrong. Nevertheless, if the timing is right, maybe I botched one of these?

The simultaneous repairs:
[li]removed head[/li]
[li]replaced hydraulic lifters[/li]
[li]cleaned carbon off valves[/li]
[li]checked pushrod straightness[/li]
[li]changed gaskets (several)[/li]
[li]replaced oil pressure sensor, coolant temp sensor, & thermostat[/li]
[li]Replaced coolant hoses[/li]

[/ul]I did all this because I hit the 150,000 mile mark and I want to keep it running for another 150,000. I would be so grateful for any help you guys can give. I’d be happy to post a video of the engine running if it will help.

That crank/cam alignment looks correct to me. You probably know this already, but it is possible for the crank/cam marks to align properly but the alignment is still wrong. That can happen b/c the crank alignment looks the same even though the crank is 360 degrees out of whack. For example, you don’t make sure the crank is at the top of the compression stroke and instead get it at the top of the exhaust stroke, that alignment will look exactly the same. right? B/c on a 4-stroke engine the crank goes around twice per cycle. Whether it would run at all if a person made that mistake, don’t know. I expect it wouldn’t, so I doubt this is your problem. But good idea to double check. I should say such a thing is not an uncommon problem reported here.

What does your scan tool say those P codes mean exactly? Perhaps while doing all this work you’ve accidentally disturbed the wiring or damaged a crank or cam position sensor? Does this poor running problem happen immediately after a cold engine is started? Or does it seem to start ok, but gets worse as the engine is warmed up? If nothing else seems to work, and you are pretty certain the valve timing is correct, and are getting a good spark at all the spark plugs, probably a compression test is the next step. You may have one or two cylinders with very low compression for some reason. is possible for the crank/cam marks to align properly but the alignment is still wrong. That can happen b/c the crank alignment looks the same even though the crank is 360 degrees out of whack.

But, if you turn the crank (only) 360 degrees, it’s right back where it started, so no change, right?

Your vehicle is OBDII. So there is no distributor adjustment for ignition timing, as this is fixed.

The codes are for the Manifold Absolute Pressure sensor.

And the MAP sensor effects ignition timing.


Do a compression test and report the numbers here.

But, if you turn the crank (only) 360 degrees, it's right back where it started, so no change, right?

My mistake. You are absolutely right. If the crank turns 360 degrees from the position shown in the photo above, the camshaft will only turn 180 degrees, so the crank could appear to be in the right alignment position, but the cam 180 degrees off. But that would be obvious by the cam’s alignment marks.

Since the codes are for the MAP sensor, if a visual inspection looks ok, one idea is to measure the manifold vacuum while all this bad behavior is happening. At idle it should be in the 17 -20 inches of mercury range. You may just have a vacuum leak going on there, and nothing wrong with the valve or ignition timing at all.

Why doesn’t the cam sprocket have a dot in it?

Usually the plug wires are put on wrong. If there is a picture of the engine (distributorless) check it out and see. If you have a distributor the rotation may go the other way than you figured. CW is clockwise and CCW is counter-clockwise. Sometimes we forget.

Your timing marks look dead on. I’ve done many of these and I don’t see anything wrong with your timing. The problem lies elsewhere.

Does your truck have an EGR valve?

Thanks so much for all your replies. This has been hugely helpful already. It’s good to eliminate the timing.

As to the ignition system (re:pleasedodgevan2), after this happened I replaced the coils and spark plug wires, so I don’t think the problem lies there.

Re: asemaster, the truck does have an EGR valve. Are you thinking it might be stuck?

Based on your replies, especially those of GeorgeSanJose, insightful, and Tester, the next steps I’m planning are: 1) test the MAP sensor and 2) if that’s good, check compression, 3) do a vacuum test. I’ll take as many of these steps as I can this afternoon and report back.

I did already look for a vacuum leak by spraying some brake cleaner around during idle, and found nothing so far. I should have mentioned that when I first started the car after the repair, it idled rough until I revved the engine a bit, then smoothed out. After putting maybe a dozen miles on it, the engine starts rough and stays rough no matter what I do, although it sounds better at higher RPMs.

Yes. An EGR valve that is sticking open or getting vacuum to open when it shouldn’t be can cause a rough idle and set a MAP sensor code.

it sounds better at higher RPMs.

That’s consistent with a vacuum leak or egr problem. One idea, it might be the MAP sensor itself is leaking vacuum. Disconnect it from the intake manifold & use a hand held vacuum pump and check it to make sure it isn’t leaking vacuum. We don’t hear many complaints here about faulty MAP sensors though. It should hold vacuum to 20 inch of mercury. That would be a good time to check the power brake booster’s ability to hold vacuum too. Likewise the fuel pressure regulator’s vacuum input. And the EGR valve often has a vacuum input. Basically you’ve got to test everything that’s vacuum connected to the intake manifold one by one and make sure none of them are leaking vacuum. Vehicles of your vintage often use vacuum to control the HVAC system vent doors, so look for vacuum lines going through the firewall and test those.

A problematic PCV hose routing or faulty PCV valve could cause this symptom too.

Today I did the vacuum pump test according to the instructions in this article: Weirdly, the sensor registered 4.97 volts no matter how much, or how little vacuum I applied. I tried replacing the MAP sensor to be sure, and tested the new one with the same result. There was no change in engine performance.

I haven’t had a chance to test the other vacuum-driven components yet. I did a compression test, and this is what I found:
1 -> 0 psi
2 -> 170 psi
3 -> 165 psi
4 -> 190 psi

I did the test on cylinder #1 three times hoping for a different result. It was difficult to thread the hose to the spark plug hole; maybe I damaged the threads looking for TDC as I rotated the engine? I used a metal bolt instead of a wooden dowel, like a fool.

Could no compression in one cylinder cause a misfire in the others? Every spark plug was badly fouled by soot when I pulled them. They were almost brand new before I did the repairs that introduced this problem.

Any suggestions you have are greatly appreciated. I’ll continue to work through the other ideas already posted.

With a dead cylinder the vacuum will be low, the computer equates low vacuum as operating under load and adds more fuel. This is why the spark plugs are fouled on the other cylinders.

Look into the compression problem on cylinder #1, you could have bent a valve if you had turned the engine without the timing chain in place.

Both MAP sensors read 4.97 volts independent of vacuum level applied …that’s a problem … hmmm … I can think of a couple reasons that might happen

  • Both MAP sensors are bad (unlikely)
  • It seems like you are, but you aren’t actually applying a vacuum to the MAP sensor input port
  • The MAP sensor ground isn’t connected to the chassis ground. I think this is the most likely explanation.

The MAP sensor – I’m presuming it is similar in design to my Corollas – has two electrical inputs (A precision +5 volts reference, and ground). And one electrical output, varying from 0 to 5 volts depending on the vacuum level. If the MAP sensor ground isn’t connected to the battery ground & chassis ground, it will always read near to +5 volts, no matter the level of vacuum applied.

The faulty MAP sensor readings (due according to my theory by a faulty ground connection) could be the cause of the soot fouled spark plugs. If it always reads a low vacuum, that tells the computer you are flooring the accelerator, so it will inject extra gas. If you actually aren’t flooring the accelerator, it will cause an overly rich condition in the cylinders and soot the spark plugs.

If I had this problem what I’d do is use a separate 5 volt bench top power supply I have laying around to power the MAP sensor with it completely removed from the car and the car’s wiring. The idea would be to decide if the problem is the MAP sensor itself, the testing method, or the car’s wiring that is causing the weird readings. I’m thinking it is the car’s wiring that’s the problem, especially likely is a grounding problem.

0 compression on cylinder number 1 is concerning. I wouldn’t expect that would cause a misfire on the other cylinders, but it depends on how the engine computer identifies a misfire. A total misfire on one cylinder I guess could slow down the crankshaft so much it might register as a misfire on the next cylinder too. Or just plain confuse the engine computer.

It might be time to call in a pro to figure out why you aren’t getting a good compression read on number one. It may be like you say, your compression tester gadget isn’t making a good seal for some reason. Or if you like to buy cool gadgets, this might be an opportunity to buy one of those vdo cameras on the end of a tube. So you can get a good look at what is going on with those threads. Don’t dismiss the use of something simple like a mirror and flashlight too. I’ve done that to check the spark plug theads on my truck and once you get the hang of it, it works pretty good.

You seem to be getting to the bottom of the problem OP. Good for you for sticking with it. Once you solve the problematic MAP sensor readings and the no compression on the first cylinder reading, I expect you’ll have thing under control.

I suspect you are reading the 5 volt computer feed to the sensor and not the MAP output, the MAP output should not exceed 4.5 volts.

When you were trying to find TDC on cylinder #1, and had the bolt on the spark plug hole. Were you using the starter motor to turn the engine…or did you use a big wrench on the crankshaft bolt.

If you used the starter, you may have either damaged a valve or popped a hole in the top of #1 piston.


Timing. Yes, the job where the plug wires were on wrong was a head replacement; not the job you did. I just remembered that you didn’t have to remove them.


The next thing you need to do is perform a leakdown test on #1 cylinder

You will very quickly determine if your problem is top end or bottom end