I forgot.....!!!! how is your crankshaft pulley? check the rubber oring that is in between it. if it is cracked and old that can through off your timing. when it spins the rubber inside the pulley plays a role in the timing....I had a crusty old one and replaced it....My problem now is my TORQUE CONVERTER THAT IS GOING OUT...AND TOO MUCH TRANNY FLUID...which is causing my hesitations....

 

Could be a bad wire harness...rare but I've seen it when all else fails...maybe a wire grounding somewhere?

 

No the crank pulley is in good shape. I have been thinking about a new harness...there is multiple points of deterioration on some insulation...the only problem is the cost. I do not dare put a used one on so will only resort to a brand new harness. I am going to talk to the shop tomorrow and see what a new one runs and install it myself if the price is not ridiculous..I have heard about $300-500? A grounding issue on a component or sensor would not be out of the question for this car. I was just crossing off wiring faults as an issue because the timing steadies out after 4k rpms....

 

I just fixed my hesitation problem.....bad transmission fluid.......replaced about 6 quarts with fresh fluid and presto....no more start or turn hesitation at all.....runs nice now....

WHY NOT A USED ONE? WELL, IF YOU CAN SHELL OUT THE CASH THEN NEW IS BETTER...I WILL HAVE TO DO THE SAME TO MINE IN THE NEAR FUTURE....BEST TO YOU...

 

Will1147, your problem seems so much like the problem I just had with my 89 740T, I wish I could tell you exactly how I fixed it, but I'm not sure if I fixed my issue or if it's just in remission. Just like your car the timing on mine was on target at 12 deg. at idle. But as soon as it was off idle the timing would retard to 9 deg, and then jump allover the place as I rev'd it up to 2k rpm. I never rev'd it higher so I don't know if it smoothed out at some point. My performance problem disappeared after I replaced a second aftermarket PowerStage with a Bosch (made in USA) power stage. Previous to the new Bosch powerStage, I had also replaced the Fuel pressure regulator, Distributor cap & rotor, Coil, AMM, cleaned and reseated the ground wires on the intake manafold, bugged out the wiring harness and sensors per TP31397. I would have also replace my plug wires but they were nearly brand new. I had bought new wires and plugs to try, but didn't get that far. Note that I tested the Coil per the Volvo manual and it passed before I replaced it. I replaced it because the 700/900 FAQ suggests a power stage can fail due to a faulty coil. It also states that resistance measurements are not a definitive test of a coil. After the problem disappeared I installed a used distributor that I had been in process of rebuilding (new Hall sensor and oil seal). A few days later I got curious and put back in one of the aftermarket Powerstages to see if I could recreate the problem.... but the car ran fine just fine.... so either my problem is not really fixed or it was a combination of flakey parts that needed replacing.

I'd also suggest trying out the Diagnostic LED on the ignition test terminal as shown in TP31397 and described in the 700/900 FAQ. I didn't get any error codes when I tried it. (this is not the same as the LED for a LH2.4 engine with ODB)

And that loop of wire that you mentioned that comes out of the connector to the FI ECU is shown in the Volvo wiring diagram (as item 886) so it is supposed to be there. No Idea why it needs to be there since it just jumpers terminal 19 to terminal 11, which is connected to ground.

 

First of all I want to say thank you everyone for the information and ideas. The car spent a week at the shop free of charge because the problem has not been fixed/found. My mechanic Terry is a great guy and the only time we usually do business together is when my resources are exhausted and it needs an expert. Well anyway he is going to wait for the same model of car to show up to the shop and check and see if it is just the nature of the car or an actual problem...I am 99% sure there is a problem but he does not want to take any more of his time looking for something that is not there.

Volvy, I have done the necessary routine maintenance on the vehicle. The power stage was also replaced with no luck. Basically everything that has to do with the ignition has been replaced, changed out or inspected. The only thing I have not replaced is the wiring harness and I do not suspect it as an issue. Terry was throwing out the idea that the ECU may be crude in its design and not cause a smooth sweep in the timing but more like a stair step effect as it goes through the RPMs. I disagree and hold to my feelings of a faulty part/sensor.

Anyways I wish I could post the solution already but as of right now it is on hold...
Thanks again

 

Alright guys. The car has spent another couple of days at a local shop in Sacramento. This shop has a good reasearch and development facility and they strapped my car on the dyno.

I crossed my fingers but they too cannot find the problem. They Know that the car is acting abnormally and because it is a manual trans the problem is more noticeable than if it was an automatic. I told the shop that I have replaced and checked almost every sensor and electronic device under the hood as well as the ignition and fuel injection ECU's.

The most recent fix was i replaced the rotting engine wiring harness hoping my problem would dissapear but it did not.

Is this issue a mechanical problem? flywheel or crankshaft issue? i checked the valve clearance and the gap was a little large although the engine was pretty hot.
It is extremely annoying to say the least and would love nothing more than to get this problem fixed. I am getting tired of investing money into a sick car. (just paid almost $400 for brand new ipd sways)

I dont know of any other local shops that know a great deal about RWD volvos otherwise I would throw them the keys as well. I am on my own here...

ANy ideas??

 

I'm going to suggest that it might be a good time to recap. That would help everyone to give good new suggestions, and bring us up fully up to date. A quick summary of the symptoms, and if they have changed at all since your original post. And a list of items replaced and tested.

 

Alright here we go...recap
Car-1987 745tic w/ m46

Symptoms behind the wheel...
The car hesitates and has a slight rocking back and forth. Almost sputtering as if running out of gas. This condition happens consistently and is between 1500 and right below 3000 rpms. It is extremely slight and you have to be on a smooth road to notice it.

Symptoms under the hood....
At first guess I thought it was a fuel issue and started throwing parts at it with consideration to the fuel. Then I put a timing light on it and when you rev the motor through the problem rpms the timing mark advances and looks correct but then it will tweak. The mark will retard around 3-6 degress very consistenly in a sharp instantenaous motion about every second or so through select rpms. The engine will also shake at the same time the mark retards. So I feel I have somewhat corned the problem but this is as far as I have gotten.

Parts replaced....
-Amm
-Fuel and ignition ECUs
-wiring harness
-o2 sensor
-knock sensor
-power stage
-ECT
-Coil
-Plugs
-Hall sensor
-Rotor
-Cap looks fine

I am starting to lean towards a mechanical issue because I have replaced some many parts with no luck and mainly this issue is so damn consistent through a set of rpms. Also if it was an electrical short or a sensor going bad I feel that it would be intermittent during different temperatures or road conditions. Also with the timing light showing a tweaking timing mark(The timing light is good) the ignition could be fine and the mark could be moving instead of the ignition timing being the wacky problem...

 

I assume Plug and coil wires are also in your list of replaced items? Since you did the wiring harness, all the grounds got reseated while you were at it? Throttle switch has been electrically tested? How is the voltage on the battery? Particularly with all the accessories on and the engine running. I think it should be around 13-14v when charging. Did you ever get to trying the diagnostic LED on the ignition ECU? It seems unlikely that your test ECU was also bad in the same way as your original, so assuming it's ok seems a good bet. It seems most likely that if there was a fault in the ignition components down stream from the ECU, that while it would affect engine performance, and could create the drive-ability symptom, it wouldn't show up in the timing. So it would have to be something up stream, and the distributor still seems the most likely place. Were your HALL sensors new or in used distributors? Signals from the ECT, Throttle switch, knock sensor, Hall sensor, could all still be suspect.

 

Yes plugs and coils were replaced. Grounds were seated well and the Battery is in good shape. Throttle switch has been sounded tested and when I slightly turn it it makes the click noise. If I unplug the throttle switch the car idles high around 1000 rpm so I assumed it was working

How would I go about electronically testing it?

The entire distributor was replaced with one from a junkyard. I found one that had been refurbished and looked brand new. When I pulled my old distributor off the shaft on the housing had about a 1/16 of an inch of play back and forth. I thought this was my problem so I put the new one in and no change. The 'new" distributor had no shaft play at all and was solid.

I tried to make a video of this timing retarding but my digital camera was not picking up the light correctly as i figured.

 

This is a long shot, but first, are the new plug and cables a suppression type with the proper resistance? Also, the wire to the hall effect sensor in the distributor, does it run parallel for any distance next to the high tension wire from the coil to the distributor. Maybe it's interfering and giving false timing signals. Like I said, it's a long shot.

 

yeah, digital camera video is usually about 15 frame or less per second, about 30 frames per second is required to look seamless to the human eye. And the flash of the timing light is probably a very small fraction of a second. One of the replies earlier suggested checking your timing belt condition, and even more so the tension. If there is some slack in the belt it could cause the timing to be jumpy. I didn't see that you had checked that. A deteriorated and thus slipping harmonic balancer? Or improperly seated rotor? At one point I had a fragment of a broken rotor lodged in my distributor not allowing the new one to seat completely.

 

I am not sure the exact type of plug wires but they are the ones for the car. The plugs are copper wr7dc as stated in the owners manual. I have looked into interference of certain types but I will agree it is a long shot.

The timing belt is good. It has about 40k miles or so and is tight. My harmonic balancer is solid as well. I am leaning towards mechanical issue because it occurs only through select rpms.... hopefully ill figure out this SOB

 

Will1147 - what happened with this?I have an 88 740 with the exact same issue. Replaced tons of crap with absolutely no change... Thanks

 

Vintage, I have owned my car for three years and have eventually learned to deal with the 'problem'. I recently purchased a '85 740 turbo with a m46 and the car did the same exact thing....I am going to have to say that it is simply the car. The lh 2.2 fuel and ignition maps may be a bit on the crude side and are not very linear in nature.

This is the only answer I have for you. I have learned to deal with the nature of the beast.

 

our 87 240 has LH 2.2, and its always pulled strong and smooth at any RPM or throttle, no hesitation unless something is wrong like inadequate fuel pumping.